API Contract Guardian

Monitor API contract drift, find data endpoints, inspect JSON payloads, and build reusable extraction recipes.

API Contract Guardian turns Chrome DevTools into a focused workspace for understanding the APIs behind modern websites. Capture Fetch and XHR traffic, infer JSON response contracts, monitor selected endpoints for schema drift, and rank the API calls most likely to populate the page you are inspecting. Give API Finder visible examples or expected field names. It combines same-site relevance, response arrays, object fields, response shape, and matching values to identify the strongest endpoint. FREE FEATURES • Capture API traffic while DevTools is open • Infer local JSON contract baselines • Pin selected contracts for drift monitoring • Detect removed fields and incompatible type changes • Search, pin, unpin, and delete saved contracts • Rank likely page-data endpoints • Ask API Finder for the most likely API and required parameters • Use Ollama locally • Bring your own OpenAI, Claude, OpenRouter, or ZenMux API key • Copy sanitized URLs and cURL commands • Pause capture when API monitoring is not needed PAYLOAD LAB PRO • $129 one-time purchase • Activate one license on up to three devices • Inspect complete captured JSON responses • Browse every JSON path returned by an API • Select array collections and map nested fields • Preview extracted rows • Export CSV, JavaScript, Guardian recipe JSON, and Loompath workflows PRIVACY Captured response bodies remain in memory for the current DevTools session and are not sent to the publisher. Contract inference, deterministic ranking, and payload extraction run inside the extension. Ollama requests remain on the user’s configured local Ollama server. External AI providers are optional and use the user’s own API key. API Finder displays an external-data warning and requires acknowledgement before sending bounded, redacted evidence to the selected provider. Authorization and cookie headers are excluded. Lemon Squeezy is contacted only when the user activates, validates, or deactivates a Pro license. HOW TO START 1. Open Chrome DevTools on a website you are authorized to inspect. 2. Select the Contract Guardian panel. 3. Reload or interact with the page. 4. Inspect traffic, pin contracts, run API Finder, or open a JSON response in Payload Lab. API Contract Guardian is intended for APIs and websites you are authorized to inspect.