MockFill: API Mocking

Intercept and mock HTTP APIs directly in your browser for frontend testing.

Mock and intercept fetch/XHR APIs in your browser with rule-based responses, delays, headers, presets, and quick toggles. MockFill: API Mocking is a developer-focused Chrome extension for mocking HTTP APIs directly in the browser. Test frontend flows without touching backend code: - Simulate success, empty, and error responses - Test loading states with response delays - Validate UI behavior for edge cases - Work faster on localhost, staging, or any web app What you can do: - Intercept both `fetch` and `XMLHttpRequest` calls - Match requests by URL pattern (string or regex) and HTTP method - Configure custom response status, body, headers, and delay - Enable/disable mocking globally or per rule - Reorder rules to control matching priority - Track hit counts for each mock rule - Import/export mock rules as JSON - Import from cURL to create rules quickly - Save presets for different testing scenarios and switch instantly Built for: - Frontend developers - QA engineers - Teams testing API-dependent UI states Why MockFill: API Mocking - No backend changes required - No external proxy setup - Fast, repeatable API testing workflow inside Chrome Privacy: - Rules and settings are stored locally in your browser. - No API payloads are sent to external servers by the extension.