APISentry - API Contract Guard 🛡️

Catch frontend ↔ backend API contract mismatches before runtime.

APISentry is a local-first, zero-config static analysis engine and extension for VS Code, Cursor, and Antigravity IDE. It statically parses your codebase to detect broken API contracts between your frontend callers (React, Next.js, Axios, Fetch) and your backend endpoints (Node.js/Express, Python FastAPI, Flask, Django REST Framework) before you run your application or deploy to production.

✨ Production Features

🛡️ Multi-Language Backend & Polyglot Engine

• Node.js / Express: Resolves complex nested router chains (app.use('/api', apiRouter), router.use('/users', usersRouter), usersRouter.get('/:id', handler)).
• Python FastAPI: Statically parses @app.get, @router.post, and extracts expected payload schemas from Pydantic models (class BaseModel).
• Python Flask: Resolves @app.route and @blueprint.route decorator verbs and route converter parameters (<int:item_id> → :item_id).
• Django REST Framework: Resolves path('api/v1/orders/', ...) route definitions and parameters.

🌐 Frontend Client Verification

• Axios & Native Fetch: Statically analyzes axios.post(), axios.get(), fetch(), custom API instances, and dynamic URL template literals.
• Zero OpenAPI/Swagger Needed: Infers API contracts directly from source code without requiring external specs or runtime server traffic.

⚡ Auto-Activation & Status Bar Health Indicator

• Instant Status Bar: Displays $(shield) APISentry: Healthy or live error counters right in your IDE status bar.
• Background File Watcher: Automatically rescans modified files in real time as you edit frontend or backend code.

🔍 Request & Response Field Diffing

• Missing Required Fields: Highlights payload fields expected by the backend but omitted in frontend API calls (e.g., missing firstName or lastName).
• Unexpected Fields: Flag fields sent by frontend that backend validators (Zod / Pydantic) do not recognize.
• HTTP Method Mismatches: Catches frontend POST requests targeted at backend PUT or GET endpoints.
• Unresolved & Broken Endpoints: Identifies frontend API calls pointing to non-existent backend routes.

📊 Production Webview & Web Preview Dashboard

• Interactive Endpoint Sidebar: Browse all discovered frontend and backend endpoints with method badges (GET, POST, PUT, DELETE).
• Click-to-Filter Issues: Click any endpoint in the sidebar to instantly filter contract issues for that endpoint.
• Responsive Dual-Panel UI: Screen-fitted dual column layout with independent scrolling and zero empty space gaps.
• One-Click Code Navigation: Click any location link (e.g., 📍 api.ts:4:10) to jump directly to the exact source code line in the editor.

🚀 How to Use

1. Open Your Project

Open any monorepo or single-repository project combining React/Next.js frontend with Express or Python backends in VS Code, Cursor, or Antigravity IDE.

2. Run Workspace Scan

• Click $(shield) APISentry in the status bar, or
• Open the Command Palette (Cmd+Shift+P / Ctrl+Shift+P) and execute APISentry: Scan Workspace.

3. Inspect Issues & Fix

• Check the API Contract Guard sidebar view in your activity bar.
• View inline squiggly diagnostics in your source files.
• Click APISentry: Open Contract Explorer to open the interactive live webview dashboard.

🛠️ Supported Tech Stack Matrix

📦 Extension Commands

📄 License

MIT © APISentry