diff --git a/.claude/settings.local.json b/.claude/settings.local.json
index cc4a06c..7f9f522 100644
--- a/.claude/settings.local.json
+++ b/.claude/settings.local.json
@@ -4,9 +4,11 @@
       "Bash(mkdir:*)",
       "Bash(uv sync:*)",
       "Bash(uv run pytest:*)",
-      "Bash(git commit:*)"
+      "Bash(git commit:*)",
+      "Bash(ruff check:*)",
+      "Bash(git add:*)"
     ],
     "deny": [],
     "ask": []
   }
-}
\ No newline at end of file
+}
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 03d6c0a..8f2edd1 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,13 +1,23 @@
 repos:
   - repo: https://github.com/charliermarsh/ruff-pre-commit
-    rev: "v0.9.1"
+    rev: "v0.12.11"
     hooks:
       - id: ruff
       - id: ruff-format
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v5.0.0
+    rev: v6.0.0
     hooks:
       - id: trailing-whitespace
         exclude: ".*\\.md$"
       - id: end-of-file-fixer
       - id: check-added-large-files
+  - repo: local
+    hooks:
+      - id: mypy
+        name: Static type check with mypy
+        entry: uv run mypy leggen leggend --check-untyped-defs
+        files: "^leggen(d)?/.*"
+        language: "system"
+        types: ["python"]
+        always_run: true
+        pass_filenames: false
diff --git a/CLAUDE.md b/CLAUDE.md
index b70f0d8..c20fe9e 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -66,4 +66,4 @@ All operations require a valid `config.toml` file with GoCardless API credential
 - `[gocardless]` - API credentials and endpoint
 - `[database]` - Storage backend selection
 - `[notifications]` - Discord/Telegram webhook settings
-- `[filters]` - Transaction matching patterns for notifications
\ No newline at end of file
+- `[filters]` - Transaction matching patterns for notifications
diff --git a/PROJECT.md b/PROJECT.md
index ebc07f0..b7a4a5a 100644
--- a/PROJECT.md
+++ b/PROJECT.md
@@ -88,4 +88,4 @@ Transform leggen from CLI-only to web application with FastAPI backend (`leggend
 - **APScheduler**: For internal job scheduling (replacing Ofelia)
 - **SvelteKit**: For modern, reactive frontend
 - **Existing Logic**: Reuse all business logic from current CLI commands
-- **Configuration**: Centralize in `leggend` service, maintain TOML compatibility
\ No newline at end of file
+- **Configuration**: Centralize in `leggend` service, maintain TOML compatibility
diff --git a/leggen/__init__.py b/leggen/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/leggen/api_client.py b/leggen/api_client.py
index 5496b52..b0a2d8d 100644
--- a/leggen/api_client.py
+++ b/leggen/api_client.py
@@ -1,6 +1,6 @@
 import os
 import requests
-from typing import Dict, Any, Optional, List
+from typing import Dict, Any, Optional, List, Union
 from urllib.parse import urljoin
 
 from leggen.utils.text import error
@@ -9,9 +9,13 @@ from leggen.utils.text import error
 class LeggendAPIClient:
     """Client for communicating with the leggend FastAPI service"""
 
+    base_url: str
+
     def __init__(self, base_url: Optional[str] = None):
-        self.base_url = base_url or os.environ.get(
-            "LEGGEND_API_URL", "http://localhost:8000"
+        self.base_url = (
+            base_url
+            or os.environ.get("LEGGEND_API_URL", "http://localhost:8000")
+            or "http://localhost:8000"
         )
         self.session = requests.Session()
         self.session.headers.update(
@@ -36,7 +40,7 @@ class LeggendAPIClient:
                 try:
                     error_data = response.json()
                     error(f"Error details: {error_data.get('detail', 'Unknown error')}")
-                except:
+                except Exception:
                     error(f"Response: {response.text}")
             raise
         except Exception as e:
@@ -48,7 +52,7 @@ class LeggendAPIClient:
         try:
             response = self._make_request("GET", "/health")
             return response.get("status") == "healthy"
-        except:
+        except Exception:
             return False
 
     # Bank endpoints
@@ -122,7 +126,7 @@ class LeggendAPIClient:
         self, days: int = 30, account_id: Optional[str] = None
     ) -> Dict[str, Any]:
         """Get transaction statistics"""
-        params = {"days": days}
+        params: Dict[str, Union[int, str]] = {"days": days}
         if account_id:
             params["account_id"] = account_id
 
@@ -141,7 +145,7 @@ class LeggendAPIClient:
         self, account_ids: Optional[List[str]] = None, force: bool = False
     ) -> Dict[str, Any]:
         """Trigger a sync"""
-        data = {"force": force}
+        data: Dict[str, Union[bool, List[str]]] = {"force": force}
         if account_ids:
             data["account_ids"] = account_ids
 
@@ -152,7 +156,7 @@ class LeggendAPIClient:
         self, account_ids: Optional[List[str]] = None, force: bool = False
     ) -> Dict[str, Any]:
         """Run sync synchronously"""
-        data = {"force": force}
+        data: Dict[str, Union[bool, List[str]]] = {"force": force}
         if account_ids:
             data["account_ids"] = account_ids
 
@@ -172,7 +176,11 @@ class LeggendAPIClient:
         cron: Optional[str] = None,
     ) -> Dict[str, Any]:
         """Update scheduler configuration"""
-        data = {"enabled": enabled, "hour": hour, "minute": minute}
+        data: Dict[str, Union[bool, int, str]] = {
+            "enabled": enabled,
+            "hour": hour,
+            "minute": minute,
+        }
         if cron:
             data["cron"] = cron
 
diff --git a/leggen/commands/bank/add.py b/leggen/commands/bank/add.py
index 8979aa7..0c66c31 100644
--- a/leggen/commands/bank/add.py
+++ b/leggen/commands/bank/add.py
@@ -68,7 +68,7 @@ def add(ctx):
 
         success("Bank connection request created successfully!")
         warning(
-            f"Please open the following URL in your browser to complete the authorization:"
+            "Please open the following URL in your browser to complete the authorization:"
         )
         click.echo(f"\n{result['link']}\n")
 
diff --git a/leggen/commands/bank/delete.py b/leggen/commands/bank/delete.py
index 66f116b..cfe3baa 100644
--- a/leggen/commands/bank/delete.py
+++ b/leggen/commands/bank/delete.py
@@ -1,7 +1,6 @@
 import click
 
 from leggen.main import cli
-from leggen.utils.network import delete as http_delete
 from leggen.utils.text import info, success
 
 
@@ -16,11 +15,12 @@ def delete(ctx, requisition_id: str):
 
     Check `leggen status` to get the REQUISITION_ID
     """
+    import requests
+
     info(f"Deleting Bank Requisition: {requisition_id}")
 
-    _ = http_delete(
-        ctx,
-        f"/requisitions/{requisition_id}",
-    )
+    api_url = ctx.obj.get("api_url", "http://localhost:8000")
+    res = requests.delete(f"{api_url}/requisitions/{requisition_id}")
+    res.raise_for_status()
 
     success(f"Bank Requisition {requisition_id} deleted")
diff --git a/leggen/commands/sync.py b/leggen/commands/sync.py
index 4becaf8..acc09d0 100644
--- a/leggen/commands/sync.py
+++ b/leggen/commands/sync.py
@@ -27,7 +27,7 @@ def sync(ctx: click.Context, wait: bool, force: bool):
             result = api_client.sync_now(force=force)
 
             if result.get("success"):
-                success(f"Sync completed successfully!")
+                success("Sync completed successfully!")
                 info(f"Accounts processed: {result.get('accounts_processed', 0)}")
                 info(f"Transactions added: {result.get('transactions_added', 0)}")
                 info(f"Balances updated: {result.get('balances_updated', 0)}")
diff --git a/leggen/main.py b/leggen/main.py
index 8859ed4..de195e5 100644
--- a/leggen/main.py
+++ b/leggen/main.py
@@ -5,7 +5,6 @@ from pathlib import Path
 
 import click
 
-from leggen.utils.auth import get_token
 from leggen.utils.config import load_config
 from leggen.utils.text import error
 
@@ -111,14 +110,4 @@ def cli(ctx: click.Context, api_url: str):
         return
 
     # Store API URL in context for commands to use
-    if api_url:
-        ctx.obj["api_url"] = api_url
-
-    # For backwards compatibility, still support direct GoCardless calls
-    # This will be used as fallback if leggend service is not available
-    try:
-        token = get_token(ctx)
-        ctx.obj["headers"] = {"Authorization": f"Bearer {token}"}
-    except Exception:
-        # If we can't get token, commands will rely on API service
-        pass
+    ctx.obj["api_url"] = api_url
diff --git a/leggen/utils/auth.py b/leggen/utils/auth.py
deleted file mode 100644
index 2f74547..0000000
--- a/leggen/utils/auth.py
+++ /dev/null
@@ -1,62 +0,0 @@
-import json
-from pathlib import Path
-
-import click
-import requests
-
-from leggen.utils.text import warning
-
-
-def create_token(ctx: click.Context) -> str:
-    """
-    Create a new token
-    """
-    res = requests.post(
-        f"{ctx.obj['gocardless']['url']}/token/new/",
-        json={
-            "secret_id": ctx.obj["gocardless"]["key"],
-            "secret_key": ctx.obj["gocardless"]["secret"],
-        },
-    )
-    res.raise_for_status()
-    auth = res.json()
-    save_auth(auth)
-    return auth["access"]
-
-
-def get_token(ctx: click.Context) -> str:
-    """
-    Get the token from the auth file or request a new one
-    """
-    auth_file = Path.home() / ".config" / "leggen" / "auth.json"
-    if auth_file.exists():
-        with click.open_file(str(auth_file), "r") as f:
-            auth = json.load(f)
-        if not auth.get("access"):
-            return create_token(ctx)
-
-        res = requests.post(
-            f"{ctx.obj['gocardless']['url']}/token/refresh/",
-            json={"refresh": auth["refresh"]},
-        )
-        try:
-            res.raise_for_status()
-            auth.update(res.json())
-            save_auth(auth)
-            return auth["access"]
-        except requests.exceptions.HTTPError:
-            warning(
-                f"Token probably expired, requesting a new one.\nResponse: {res.status_code}\n{res.text}"
-            )
-            return create_token(ctx)
-    else:
-        return create_token(ctx)
-
-
-def save_auth(d: dict):
-    auth_dir = Path.home() / ".config" / "leggen"
-    auth_dir.mkdir(parents=True, exist_ok=True)
-    auth_file = auth_dir / "auth.json"
-
-    with click.open_file(str(auth_file), "w") as f:
-        json.dump(d, f)
diff --git a/leggen/utils/database.py b/leggen/utils/database.py
index 6c5cab5..c1ce9e2 100644
--- a/leggen/utils/database.py
+++ b/leggen/utils/database.py
@@ -3,7 +3,6 @@ from datetime import datetime
 import click
 
 import leggen.database.sqlite as sqlite_engine
-from leggen.utils.network import get
 from leggen.utils.text import info, warning
 
 
@@ -32,15 +31,21 @@ def persist_transactions(ctx: click.Context, account: str, transactions: list) -
 
 
 def save_transactions(ctx: click.Context, account: str) -> list:
+    import requests
+
+    api_url = ctx.obj.get("api_url", "http://localhost:8000")
+
     info(f"[{account}] Getting account details")
-    account_info = get(ctx, f"/accounts/{account}")
+    res = requests.get(f"{api_url}/accounts/{account}")
+    res.raise_for_status()
+    account_info = res.json()
 
     info(f"[{account}] Getting transactions")
     transactions = []
 
-    account_transactions = get(ctx, f"/accounts/{account}/transactions/").get(
-        "transactions", []
-    )
+    res = requests.get(f"{api_url}/accounts/{account}/transactions/")
+    res.raise_for_status()
+    account_transactions = res.json().get("transactions", [])
 
     for transaction in account_transactions.get("booked", []):
         booked_date = transaction.get("bookingDateTime") or transaction.get(
diff --git a/leggen/utils/network.py b/leggen/utils/network.py
deleted file mode 100644
index 242fd7c..0000000
--- a/leggen/utils/network.py
+++ /dev/null
@@ -1,64 +0,0 @@
-import click
-import requests
-
-from leggen.utils.text import error
-
-
-def get(ctx: click.Context, path: str, params: dict = {}):
-    """
-    GET request to the GoCardless API
-    """
-
-    url = f"{ctx.obj['gocardless']['url']}{path}"
-    res = requests.get(url, headers=ctx.obj["headers"], params=params)
-    try:
-        res.raise_for_status()
-    except Exception as e:
-        error(f"Error: {e}\n{res.text}")
-        ctx.abort()
-    return res.json()
-
-
-def post(ctx: click.Context, path: str, data: dict = {}):
-    """
-    POST request to the GoCardless API
-    """
-
-    url = f"{ctx.obj['gocardless']['url']}{path}"
-    res = requests.post(url, headers=ctx.obj["headers"], json=data)
-    try:
-        res.raise_for_status()
-    except Exception as e:
-        error(f"Error: {e}\n{res.text}")
-        ctx.abort()
-    return res.json()
-
-
-def put(ctx: click.Context, path: str, data: dict = {}):
-    """
-    PUT request to the GoCardless API
-    """
-
-    url = f"{ctx.obj['gocardless']['url']}{path}"
-    res = requests.put(url, headers=ctx.obj["headers"], json=data)
-    try:
-        res.raise_for_status()
-    except Exception as e:
-        error(f"Error: {e}\n{res.text}")
-        ctx.abort()
-    return res.json()
-
-
-def delete(ctx: click.Context, path: str):
-    """
-    DELETE request to the GoCardless API
-    """
-
-    url = f"{ctx.obj['gocardless']['url']}{path}"
-    res = requests.delete(url, headers=ctx.obj["headers"])
-    try:
-        res.raise_for_status()
-    except Exception as e:
-        error(f"Error: {e}\n{res.text}")
-        ctx.abort()
-    return res.json()
diff --git a/leggend/__init__.py b/leggend/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/leggend/api/models/common.py b/leggend/api/models/common.py
index 626368e..c2a056d 100644
--- a/leggend/api/models/common.py
+++ b/leggend/api/models/common.py
@@ -1,4 +1,3 @@
-from datetime import datetime
 from typing import Any, Dict, Optional
 
 from pydantic import BaseModel
diff --git a/leggend/api/models/notifications.py b/leggend/api/models/notifications.py
index c966886..20541ca 100644
--- a/leggend/api/models/notifications.py
+++ b/leggend/api/models/notifications.py
@@ -1,4 +1,4 @@
-from typing import Dict, Any, Optional, List
+from typing import Dict, Optional, List
 
 from pydantic import BaseModel
 
diff --git a/leggend/api/models/sync.py b/leggend/api/models/sync.py
index 44bd9c7..a49321c 100644
--- a/leggend/api/models/sync.py
+++ b/leggend/api/models/sync.py
@@ -1,5 +1,5 @@
 from datetime import datetime
-from typing import Optional, Dict, Any
+from typing import Optional
 
 from pydantic import BaseModel
 
diff --git a/leggend/api/routes/accounts.py b/leggend/api/routes/accounts.py
index 57549f2..bddc413 100644
--- a/leggend/api/routes/accounts.py
+++ b/leggend/api/routes/accounts.py
@@ -1,4 +1,4 @@
-from typing import List, Optional
+from typing import Optional, List, Union
 from fastapi import APIRouter, HTTPException, Query
 from loguru import logger
 
@@ -74,7 +74,9 @@ async def get_all_accounts() -> APIResponse:
 
     except Exception as e:
         logger.error(f"Failed to get accounts: {e}")
-        raise HTTPException(status_code=500, detail=f"Failed to get accounts: {str(e)}")
+        raise HTTPException(
+            status_code=500, detail=f"Failed to get accounts: {str(e)}"
+        ) from e
 
 
 @router.get("/accounts/{account_id}", response_model=APIResponse)
@@ -117,7 +119,9 @@ async def get_account_details(account_id: str) -> APIResponse:
 
     except Exception as e:
         logger.error(f"Failed to get account details for {account_id}: {e}")
-        raise HTTPException(status_code=404, detail=f"Account not found: {str(e)}")
+        raise HTTPException(
+            status_code=404, detail=f"Account not found: {str(e)}"
+        ) from e
 
 
 @router.get("/accounts/{account_id}/balances", response_model=APIResponse)
@@ -146,7 +150,9 @@ async def get_account_balances(account_id: str) -> APIResponse:
 
     except Exception as e:
         logger.error(f"Failed to get balances for account {account_id}: {e}")
-        raise HTTPException(status_code=404, detail=f"Failed to get balances: {str(e)}")
+        raise HTTPException(
+            status_code=404, detail=f"Failed to get balances: {str(e)}"
+        ) from e
 
 
 @router.get("/accounts/{account_id}/transactions", response_model=APIResponse)
@@ -172,11 +178,17 @@ async def get_account_transactions(
 
         # Apply pagination
         total_transactions = len(processed_transactions)
-        paginated_transactions = processed_transactions[offset : offset + limit]
+        actual_offset = offset or 0
+        actual_limit = limit or 100
+        paginated_transactions = processed_transactions[
+            actual_offset : actual_offset + actual_limit
+        ]
+
+        data: Union[List[TransactionSummary], List[Transaction]]
 
         if summary_only:
             # Return simplified transaction summaries
-            summaries = [
+            data = [
                 TransactionSummary(
                     internal_transaction_id=txn["internalTransactionId"],
                     date=txn["transactionDate"],
@@ -188,10 +200,9 @@ async def get_account_transactions(
                 )
                 for txn in paginated_transactions
             ]
-            data = summaries
         else:
             # Return full transaction details
-            transactions = [
+            data = [
                 Transaction(
                     internal_transaction_id=txn["internalTransactionId"],
                     institution_id=txn["institutionId"],
@@ -206,16 +217,15 @@ async def get_account_transactions(
                 )
                 for txn in paginated_transactions
             ]
-            data = transactions
 
         return APIResponse(
             success=True,
             data=data,
-            message=f"Retrieved {len(data)} transactions (showing {offset + 1}-{offset + len(data)} of {total_transactions})",
+            message=f"Retrieved {len(data)} transactions (showing {actual_offset + 1}-{actual_offset + len(data)} of {total_transactions})",
         )
 
     except Exception as e:
         logger.error(f"Failed to get transactions for account {account_id}: {e}")
         raise HTTPException(
             status_code=404, detail=f"Failed to get transactions: {str(e)}"
-        )
+        ) from e
diff --git a/leggend/api/routes/banks.py b/leggend/api/routes/banks.py
index 27f4a38..7368fea 100644
--- a/leggend/api/routes/banks.py
+++ b/leggend/api/routes/banks.py
@@ -1,8 +1,7 @@
-from typing import List, Optional
 from fastapi import APIRouter, HTTPException, Query
 from loguru import logger
 
-from leggend.api.models.common import APIResponse, ErrorResponse
+from leggend.api.models.common import APIResponse
 from leggend.api.models.banks import (
     BankInstitution,
     BankConnectionRequest,
@@ -46,15 +45,16 @@ async def get_bank_institutions(
         logger.error(f"Failed to get institutions for {country}: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get institutions: {str(e)}"
-        )
+        ) from e
 
 
 @router.post("/banks/connect", response_model=APIResponse)
 async def connect_to_bank(request: BankConnectionRequest) -> APIResponse:
     """Create a connection to a bank (requisition)"""
     try:
+        redirect_url = request.redirect_url or "http://localhost:8000/"
         requisition_data = await gocardless_service.create_requisition(
-            request.institution_id, request.redirect_url
+            request.institution_id, redirect_url
         )
 
         requisition = BankRequisition(
@@ -69,14 +69,14 @@ async def connect_to_bank(request: BankConnectionRequest) -> APIResponse:
         return APIResponse(
             success=True,
             data=requisition,
-            message=f"Bank connection created. Please visit the link to authorize.",
+            message="Bank connection created. Please visit the link to authorize.",
         )
 
     except Exception as e:
         logger.error(f"Failed to connect to bank {request.institution_id}: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to connect to bank: {str(e)}"
-        )
+        ) from e
 
 
 @router.get("/banks/status", response_model=APIResponse)
@@ -114,7 +114,7 @@ async def get_bank_connections_status() -> APIResponse:
         logger.error(f"Failed to get bank connection status: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get bank status: {str(e)}"
-        )
+        ) from e
 
 
 @router.delete("/banks/connections/{requisition_id}", response_model=APIResponse)
@@ -132,7 +132,7 @@ async def delete_bank_connection(requisition_id: str) -> APIResponse:
         logger.error(f"Failed to delete bank connection {requisition_id}: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to delete connection: {str(e)}"
-        )
+        ) from e
 
 
 @router.get("/banks/countries", response_model=APIResponse)
diff --git a/leggend/api/routes/notifications.py b/leggend/api/routes/notifications.py
index 6bc6558..bb009e1 100644
--- a/leggend/api/routes/notifications.py
+++ b/leggend/api/routes/notifications.py
@@ -1,4 +1,4 @@
-from typing import Optional
+from typing import Dict, Any
 from fastapi import APIRouter, HTTPException
 from loguru import logger
 
@@ -60,7 +60,7 @@ async def get_notification_settings() -> APIResponse:
         logger.error(f"Failed to get notification settings: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get notification settings: {str(e)}"
-        )
+        ) from e
 
 
 @router.put("/notifications/settings", response_model=APIResponse)
@@ -84,7 +84,7 @@ async def update_notification_settings(settings: NotificationSettings) -> APIRes
             }
 
         # Update filters config
-        filters_config = {}
+        filters_config: Dict[str, Any] = {}
         if settings.filters.case_insensitive:
             filters_config["case-insensitive"] = settings.filters.case_insensitive
         if settings.filters.case_sensitive:
@@ -110,7 +110,7 @@ async def update_notification_settings(settings: NotificationSettings) -> APIRes
         logger.error(f"Failed to update notification settings: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to update notification settings: {str(e)}"
-        )
+        ) from e
 
 
 @router.post("/notifications/test", response_model=APIResponse)
@@ -137,7 +137,7 @@ async def test_notification(test_request: NotificationTest) -> APIResponse:
         logger.error(f"Failed to send test notification: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to send test notification: {str(e)}"
-        )
+        ) from e
 
 
 @router.get("/notifications/services", response_model=APIResponse)
@@ -179,7 +179,7 @@ async def get_notification_services() -> APIResponse:
         logger.error(f"Failed to get notification services: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get notification services: {str(e)}"
-        )
+        ) from e
 
 
 @router.delete("/notifications/settings/{service}", response_model=APIResponse)
@@ -206,4 +206,4 @@ async def delete_notification_service(service: str) -> APIResponse:
         logger.error(f"Failed to delete notification service {service}: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to delete notification service: {str(e)}"
-        )
+        ) from e
diff --git a/leggend/api/routes/sync.py b/leggend/api/routes/sync.py
index a7f1e92..0de823f 100644
--- a/leggend/api/routes/sync.py
+++ b/leggend/api/routes/sync.py
@@ -3,7 +3,7 @@ from fastapi import APIRouter, HTTPException, BackgroundTasks
 from loguru import logger
 
 from leggend.api.models.common import APIResponse
-from leggend.api.models.sync import SyncRequest, SyncStatus, SyncResult, SchedulerConfig
+from leggend.api.models.sync import SyncRequest, SchedulerConfig
 from leggend.services.sync_service import SyncService
 from leggend.background.scheduler import scheduler
 from leggend.config import config
@@ -31,7 +31,7 @@ async def get_sync_status() -> APIResponse:
         logger.error(f"Failed to get sync status: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get sync status: {str(e)}"
-        )
+        ) from e
 
 
 @router.post("/sync", response_model=APIResponse)
@@ -78,7 +78,9 @@ async def trigger_sync(
 
     except Exception as e:
         logger.error(f"Failed to trigger sync: {e}")
-        raise HTTPException(status_code=500, detail=f"Failed to trigger sync: {str(e)}")
+        raise HTTPException(
+            status_code=500, detail=f"Failed to trigger sync: {str(e)}"
+        ) from e
 
 
 @router.post("/sync/now", response_model=APIResponse)
@@ -104,7 +106,9 @@ async def sync_now(sync_request: Optional[SyncRequest] = None) -> APIResponse:
 
     except Exception as e:
         logger.error(f"Failed to run sync: {e}")
-        raise HTTPException(status_code=500, detail=f"Failed to run sync: {str(e)}")
+        raise HTTPException(
+            status_code=500, detail=f"Failed to run sync: {str(e)}"
+        ) from e
 
 
 @router.get("/sync/scheduler", response_model=APIResponse)
@@ -134,7 +138,7 @@ async def get_scheduler_config() -> APIResponse:
         logger.error(f"Failed to get scheduler config: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get scheduler config: {str(e)}"
-        )
+        ) from e
 
 
 @router.put("/sync/scheduler", response_model=APIResponse)
@@ -152,7 +156,7 @@ async def update_scheduler_config(scheduler_config: SchedulerConfig) -> APIRespo
             except Exception as e:
                 raise HTTPException(
                     status_code=400, detail=f"Invalid cron expression: {str(e)}"
-                )
+                ) from e
 
         # Update configuration
         schedule_data = scheduler_config.dict(exclude_none=True)
@@ -171,7 +175,7 @@ async def update_scheduler_config(scheduler_config: SchedulerConfig) -> APIRespo
         logger.error(f"Failed to update scheduler config: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to update scheduler config: {str(e)}"
-        )
+        ) from e
 
 
 @router.post("/sync/scheduler/start", response_model=APIResponse)
@@ -188,7 +192,7 @@ async def start_scheduler() -> APIResponse:
         logger.error(f"Failed to start scheduler: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to start scheduler: {str(e)}"
-        )
+        ) from e
 
 
 @router.post("/sync/scheduler/stop", response_model=APIResponse)
@@ -205,4 +209,4 @@ async def stop_scheduler() -> APIResponse:
         logger.error(f"Failed to stop scheduler: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to stop scheduler: {str(e)}"
-        )
+        ) from e
diff --git a/leggend/api/routes/transactions.py b/leggend/api/routes/transactions.py
index 633e9a0..afb62c3 100644
--- a/leggend/api/routes/transactions.py
+++ b/leggend/api/routes/transactions.py
@@ -1,4 +1,4 @@
-from typing import List, Optional
+from typing import Optional, List, Union
 from datetime import datetime, timedelta
 from fastapi import APIRouter, HTTPException, Query
 from loguru import logger
@@ -120,7 +120,13 @@ async def get_all_transactions(
 
         # Apply pagination
         total_transactions = len(filtered_transactions)
-        paginated_transactions = filtered_transactions[offset : offset + limit]
+        actual_offset = offset or 0
+        actual_limit = limit or 100
+        paginated_transactions = filtered_transactions[
+            actual_offset : actual_offset + actual_limit
+        ]
+
+        data: Union[List[TransactionSummary], List[Transaction]]
 
         if summary_only:
             # Return simplified transaction summaries
@@ -157,14 +163,14 @@ async def get_all_transactions(
         return APIResponse(
             success=True,
             data=data,
-            message=f"Retrieved {len(data)} transactions (showing {offset + 1}-{offset + len(data)} of {total_transactions})",
+            message=f"Retrieved {len(data)} transactions (showing {actual_offset + 1}-{actual_offset + len(data)} of {total_transactions})",
         )
 
     except Exception as e:
         logger.error(f"Failed to get transactions: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get transactions: {str(e)}"
-        )
+        ) from e
 
 
 @router.get("/transactions/stats", response_model=APIResponse)
@@ -270,4 +276,4 @@ async def get_transaction_stats(
         logger.error(f"Failed to get transaction stats: {e}")
         raise HTTPException(
             status_code=500, detail=f"Failed to get transaction stats: {str(e)}"
-        )
+        ) from e
diff --git a/leggend/config.py b/leggend/config.py
index b09e180..336434e 100644
--- a/leggend/config.py
+++ b/leggend/config.py
@@ -17,7 +17,7 @@ class Config:
             cls._instance = super().__new__(cls)
         return cls._instance
 
-    def load_config(self, config_path: str = None) -> Dict[str, Any]:
+    def load_config(self, config_path: Optional[str] = None) -> Dict[str, Any]:
         if self._config is not None:
             return self._config
 
@@ -43,7 +43,9 @@ class Config:
         return self._config
 
     def save_config(
-        self, config_data: Dict[str, Any] = None, config_path: str = None
+        self,
+        config_data: Optional[Dict[str, Any]] = None,
+        config_path: Optional[str] = None,
     ) -> None:
         """Save configuration to TOML file"""
         if config_data is None:
@@ -55,6 +57,11 @@ class Config:
                 str(Path.home() / ".config" / "leggen" / "config.toml"),
             )
 
+        if config_path is None:
+            raise ValueError("No config path specified")
+        if config_data is None:
+            raise ValueError("No config data to save")
+
         # Ensure directory exists
         Path(config_path).parent.mkdir(parents=True, exist_ok=True)
 
@@ -75,6 +82,9 @@ class Config:
         if self._config is None:
             self.load_config()
 
+        if self._config is None:
+            raise RuntimeError("Failed to load config")
+
         if section not in self._config:
             self._config[section] = {}
 
@@ -86,6 +96,9 @@ class Config:
         if self._config is None:
             self.load_config()
 
+        if self._config is None:
+            raise RuntimeError("Failed to load config")
+
         self._config[section] = data
         self.save_config()
 
@@ -93,6 +106,8 @@ class Config:
     def config(self) -> Dict[str, Any]:
         if self._config is None:
             self.load_config()
+        if self._config is None:
+            raise RuntimeError("Failed to load config")
         return self._config
 
     @property
diff --git a/leggend/main.py b/leggend/main.py
index 1693803..397edce 100644
--- a/leggend/main.py
+++ b/leggend/main.py
@@ -1,4 +1,3 @@
-import asyncio
 from contextlib import asynccontextmanager
 from importlib import metadata
 
diff --git a/leggend/services/database_service.py b/leggend/services/database_service.py
index 87b7911..dc4a1a6 100644
--- a/leggend/services/database_service.py
+++ b/leggend/services/database_service.py
@@ -1,5 +1,5 @@
 from datetime import datetime
-from typing import List, Dict, Any, Optional
+from typing import List, Dict, Any
 
 from loguru import logger
 
@@ -75,7 +75,10 @@ class DatabaseService:
                 datetime.fromisoformat(booked_date), datetime.fromisoformat(value_date)
             )
         else:
-            min_date = datetime.fromisoformat(booked_date or value_date)
+            date_str = booked_date or value_date
+            if not date_str:
+                raise ValueError("No valid date found in transaction")
+            min_date = datetime.fromisoformat(date_str)
 
         # Extract amount and currency
         transaction_amount = transaction.get("transactionAmount", {})
diff --git a/leggend/services/gocardless_service.py b/leggend/services/gocardless_service.py
index 073c83a..4a58293 100644
--- a/leggend/services/gocardless_service.py
+++ b/leggend/services/gocardless_service.py
@@ -1,8 +1,7 @@
-import asyncio
 import json
 import httpx
 from pathlib import Path
-from typing import Dict, Any, List, Optional
+from typing import Dict, Any, List
 
 from loguru import logger
 
diff --git a/leggend/services/notification_service.py b/leggend/services/notification_service.py
index 8d29fd7..c684476 100644
--- a/leggend/services/notification_service.py
+++ b/leggend/services/notification_service.py
@@ -69,7 +69,7 @@ class NotificationService:
             description = transaction.get("description", "").lower()
 
             # Check case-insensitive filters
-            for filter_name, filter_value in filters_case_insensitive.items():
+            for _filter_name, filter_value in filters_case_insensitive.items():
                 if filter_value.lower() in description:
                     matching.append(
                         {
diff --git a/leggend/services/sync_service.py b/leggend/services/sync_service.py
index ba9d14a..62815a8 100644
--- a/leggend/services/sync_service.py
+++ b/leggend/services/sync_service.py
@@ -1,10 +1,8 @@
-import asyncio
 from datetime import datetime
-from typing import List, Dict, Any
+from typing import List
 
 from loguru import logger
 
-from leggend.config import config
 from leggend.api.models.sync import SyncResult, SyncStatus
 from leggend.services.gocardless_service import GoCardlessService
 from leggend.services.database_service import DatabaseService
diff --git a/pyproject.toml b/pyproject.toml
index 9f14908..28372ba 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -49,9 +49,12 @@ dev = [
     "pre-commit>=3.6.0",
     "pytest>=8.0.0",
     "pytest-asyncio>=0.23.0",
-    "pytest-mock>=3.12.0", 
+    "pytest-mock>=3.12.0",
     "respx>=0.21.0",
     "requests-mock>=1.12.0",
+    "mypy>=1.17.1",
+    "types-tabulate>=0.9.0.20241207",
+    "types-requests>=2.32.4.20250809",
 ]
 
 [tool.hatch.build.targets.sdist]
@@ -71,20 +74,19 @@ lint.extend-select = ["B", "C4", "PIE", "T20", "SIM", "TCH"]
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 python_files = "test_*.py"
-python_classes = "Test*" 
+python_classes = "Test*"
 python_functions = "test_*"
-addopts = [
-    "-v",
-    "--tb=short", 
-    "--strict-markers",
-    "--disable-warnings"
-]
+addopts = ["-v", "--tb=short", "--strict-markers", "--disable-warnings"]
 asyncio_mode = "auto"
 asyncio_default_fixture_loop_scope = "function"
 markers = [
     "unit: Unit tests",
     "integration: Integration tests",
-    "slow: Slow running tests", 
+    "slow: Slow running tests",
     "api: API endpoint tests",
-    "cli: CLI command tests"
+    "cli: CLI command tests",
 ]
+
+[[tool.mypy.overrides]]
+module = ["apscheduler.*"]
+ignore_missing_imports = true
diff --git a/tests/unit/test_api_banks.py b/tests/unit/test_api_banks.py
index 7746b47..b3bfea7 100644
--- a/tests/unit/test_api_banks.py
+++ b/tests/unit/test_api_banks.py
@@ -5,8 +5,6 @@ import respx
 import httpx
 from unittest.mock import patch
 
-from leggend.services.gocardless_service import GoCardlessService
-
 
 @pytest.mark.api
 class TestBanksAPI:
diff --git a/tests/unit/test_api_client.py b/tests/unit/test_api_client.py
index 75f8c0d..c1d4282 100644
--- a/tests/unit/test_api_client.py
+++ b/tests/unit/test_api_client.py
@@ -1,6 +1,7 @@
 """Tests for CLI API client."""
 
 import pytest
+import requests
 import requests_mock
 from unittest.mock import patch
 
@@ -85,7 +86,7 @@ class TestLeggendAPIClient:
         """Test handling of connection errors."""
         client = LeggendAPIClient("http://localhost:9999")  # Non-existent service
 
-        with pytest.raises(Exception):
+        with pytest.raises((requests.ConnectionError, requests.RequestException)):
             client.get_accounts()
 
     def test_http_error_handling(self):
@@ -99,7 +100,7 @@ class TestLeggendAPIClient:
                 json={"detail": "Internal server error"},
             )
 
-            with pytest.raises(Exception):
+            with pytest.raises((requests.HTTPError, requests.RequestException)):
                 client.get_accounts()
 
     def test_custom_api_url(self):
diff --git a/tests/unit/test_config.py b/tests/unit/test_config.py
index 4aeecf7..c26f151 100644
--- a/tests/unit/test_config.py
+++ b/tests/unit/test_config.py
@@ -1,8 +1,6 @@
 """Tests for configuration management."""
 
 import pytest
-import tempfile
-from pathlib import Path
 from unittest.mock import patch
 
 from leggend.config import Config
@@ -164,9 +162,11 @@ class TestConfig:
             config = Config()
             config._config = None
 
-            with patch("builtins.open", side_effect=FileNotFoundError):
-                with pytest.raises(FileNotFoundError):
-                    config.load_config()
+            with (
+                patch("builtins.open", side_effect=FileNotFoundError),
+                pytest.raises(FileNotFoundError),
+            ):
+                config.load_config()
 
     def test_notifications_config(self):
         """Test notifications configuration access."""
diff --git a/tests/unit/test_scheduler.py b/tests/unit/test_scheduler.py
index a32c933..cb05d72 100644
--- a/tests/unit/test_scheduler.py
+++ b/tests/unit/test_scheduler.py
@@ -1,13 +1,10 @@
 """Tests for background scheduler."""
 
 import pytest
-import asyncio
-from unittest.mock import Mock, patch, AsyncMock, MagicMock
+from unittest.mock import patch, AsyncMock, MagicMock
 from datetime import datetime
-from apscheduler.schedulers.blocking import BlockingScheduler
 
 from leggend.background.scheduler import BackgroundScheduler
-from leggend.services.sync_service import SyncService
 
 
 @pytest.mark.unit
diff --git a/uv.lock b/uv.lock
index 713ec79..7a2a6d2 100644
--- a/uv.lock
+++ b/uv.lock
@@ -240,6 +240,7 @@ dependencies = [
 
 [package.dev-dependencies]
 dev = [
+    { name = "mypy" },
     { name = "pre-commit" },
     { name = "pytest" },
     { name = "pytest-asyncio" },
@@ -247,6 +248,8 @@ dev = [
     { name = "requests-mock" },
     { name = "respx" },
     { name = "ruff" },
+    { name = "types-requests" },
+    { name = "types-tabulate" },
 ]
 
 [package.metadata]
@@ -265,6 +268,7 @@ requires-dist = [
 
 [package.metadata.requires-dev]
 dev = [
+    { name = "mypy", specifier = ">=1.17.1" },
     { name = "pre-commit", specifier = ">=3.6.0" },
     { name = "pytest", specifier = ">=8.0.0" },
     { name = "pytest-asyncio", specifier = ">=0.23.0" },
@@ -272,6 +276,8 @@ dev = [
     { name = "requests-mock", specifier = ">=1.12.0" },
     { name = "respx", specifier = ">=0.21.0" },
     { name = "ruff", specifier = ">=0.6.1" },
+    { name = "types-requests", specifier = ">=2.32.4.20250809" },
+    { name = "types-tabulate", specifier = ">=0.9.0.20241207" },
 ]
 
 [[package]]
@@ -287,6 +293,35 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/0c/29/0348de65b8cc732daa3e33e67806420b2ae89bdce2b04af740289c5c6c8c/loguru-0.7.3-py3-none-any.whl", hash = "sha256:31a33c10c8e1e10422bfd431aeb5d351c7cf7fa671e3c4df004162264b28220c", size = 61595, upload-time = "2024-12-06T11:20:54.538Z" },
 ]
 
+[[package]]
+name = "mypy"
+version = "1.17.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "mypy-extensions" },
+    { name = "pathspec" },
+    { name = "typing-extensions" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/8e/22/ea637422dedf0bf36f3ef238eab4e455e2a0dcc3082b5cc067615347ab8e/mypy-1.17.1.tar.gz", hash = "sha256:25e01ec741ab5bb3eec8ba9cdb0f769230368a22c959c4937360efb89b7e9f01", size = 3352570, upload-time = "2025-07-31T07:54:19.204Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/17/a2/7034d0d61af8098ec47902108553122baa0f438df8a713be860f7407c9e6/mypy-1.17.1-cp312-cp312-macosx_10_13_x86_64.whl", hash = "sha256:69e83ea6553a3ba79c08c6e15dbd9bfa912ec1e493bf75489ef93beb65209aeb", size = 11086295, upload-time = "2025-07-31T07:53:28.124Z" },
+    { url = "https://files.pythonhosted.org/packages/14/1f/19e7e44b594d4b12f6ba8064dbe136505cec813549ca3e5191e40b1d3cc2/mypy-1.17.1-cp312-cp312-macosx_11_0_arm64.whl", hash = "sha256:1b16708a66d38abb1e6b5702f5c2c87e133289da36f6a1d15f6a5221085c6403", size = 10112355, upload-time = "2025-07-31T07:53:21.121Z" },
+    { url = "https://files.pythonhosted.org/packages/5b/69/baa33927e29e6b4c55d798a9d44db5d394072eef2bdc18c3e2048c9ed1e9/mypy-1.17.1-cp312-cp312-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:89e972c0035e9e05823907ad5398c5a73b9f47a002b22359b177d40bdaee7056", size = 11875285, upload-time = "2025-07-31T07:53:55.293Z" },
+    { url = "https://files.pythonhosted.org/packages/90/13/f3a89c76b0a41e19490b01e7069713a30949d9a6c147289ee1521bcea245/mypy-1.17.1-cp312-cp312-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:03b6d0ed2b188e35ee6d5c36b5580cffd6da23319991c49ab5556c023ccf1341", size = 12737895, upload-time = "2025-07-31T07:53:43.623Z" },
+    { url = "https://files.pythonhosted.org/packages/23/a1/c4ee79ac484241301564072e6476c5a5be2590bc2e7bfd28220033d2ef8f/mypy-1.17.1-cp312-cp312-musllinux_1_2_x86_64.whl", hash = "sha256:c837b896b37cd103570d776bda106eabb8737aa6dd4f248451aecf53030cdbeb", size = 12931025, upload-time = "2025-07-31T07:54:17.125Z" },
+    { url = "https://files.pythonhosted.org/packages/89/b8/7409477be7919a0608900e6320b155c72caab4fef46427c5cc75f85edadd/mypy-1.17.1-cp312-cp312-win_amd64.whl", hash = "sha256:665afab0963a4b39dff7c1fa563cc8b11ecff7910206db4b2e64dd1ba25aed19", size = 9584664, upload-time = "2025-07-31T07:54:12.842Z" },
+    { url = "https://files.pythonhosted.org/packages/1d/f3/8fcd2af0f5b806f6cf463efaffd3c9548a28f84220493ecd38d127b6b66d/mypy-1.17.1-py3-none-any.whl", hash = "sha256:a9f52c0351c21fe24c21d8c0eb1f62967b262d6729393397b6f443c3b773c3b9", size = 2283411, upload-time = "2025-07-31T07:53:24.664Z" },
+]
+
+[[package]]
+name = "mypy-extensions"
+version = "1.1.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/a2/6e/371856a3fb9d31ca8dac321cda606860fa4548858c0cc45d9d1d4ca2628b/mypy_extensions-1.1.0.tar.gz", hash = "sha256:52e68efc3284861e772bbcd66823fde5ae21fd2fdb51c62a211403730b916558", size = 6343, upload-time = "2025-04-22T14:54:24.164Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/79/7b/2c79738432f5c924bef5071f933bcc9efd0473bac3b4aa584a6f7c1c8df8/mypy_extensions-1.1.0-py3-none-any.whl", hash = "sha256:1be4cccdb0f2482337c4743e60421de3a356cd97508abadd57d47403e94f5505", size = 4963, upload-time = "2025-04-22T14:54:22.983Z" },
+]
+
 [[package]]
 name = "nodeenv"
 version = "1.9.1"
@@ -305,6 +340,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/20/12/38679034af332785aac8774540895e234f4d07f7545804097de4b666afd8/packaging-25.0-py3-none-any.whl", hash = "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484", size = 66469, upload-time = "2025-04-19T11:48:57.875Z" },
 ]
 
+[[package]]
+name = "pathspec"
+version = "0.12.1"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/ca/bc/f35b8446f4531a7cb215605d100cd88b7ac6f44ab3fc94870c120ab3adbf/pathspec-0.12.1.tar.gz", hash = "sha256:a482d51503a1ab33b1c67a6c3813a26953dbdc71c31dacaef9a838c4e29f5712", size = 51043, upload-time = "2023-12-10T22:30:45Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/cc/20/ff623b09d963f88bfde16306a54e12ee5ea43e9b597108672ff3a408aad6/pathspec-0.12.1-py3-none-any.whl", hash = "sha256:a0d503e138a4c123b27490a4f7beda6a01c6f288df0e4a8b79c7eb0dc7b4cc08", size = 31191, upload-time = "2023-12-10T22:30:43.14Z" },
+]
+
 [[package]]
 name = "platformdirs"
 version = "4.3.6"
@@ -558,6 +602,27 @@ wheels = [
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+wheels = [
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 name = "typing-extensions"
 version = "4.15.0"