A high-performance, open-source Chrome extension (Manifest V3) that brings a Postman-like workflow directly into your browser's DevTools. XApi intercepts, debugs, edits, and replays HTTP requests — with first-class support for modifying sensitive headers such as Cookie, Origin, and Referer, mocking responses, and injecting request headers globally.

Debug directly while you browse without switching tabs, and manage collections and complex requests in a dedicated window.

• Automatically capture Fetch and XHR traffic from the active tab.
• Edit any captured request's body, headers, or query parameters and replay it with one click.
• Paste raw cURL commands to instantly generate fully editable request objects.
• Organize requests into nested collections with persistent storage.

Inject or override request headers across every XHR/Fetch call, without editing individual requests.

• Managed from the Header tab in the extension popup, backed by Chrome's declarativeNetRequest (DNR) engine.
• Each header row has an enable checkbox, a key, and a value; toggle rows individually and flip the global master switch to activate all enabled headers at once.
• Headers are applied as SET operations, so they add the header when absent and override it when present.
• Scope is limited to XMLHttpRequest resources, matching XApi's capture range, and the rule is rebuilt automatically whenever you change a header or toggle the switch.
• Because it runs through DNR, it can set headers the browser normally protects — including Cookie, Origin, and Referer — that page scripts cannot change on their own.
• Global header rules use a dedicated DNR rule and a lower priority than one-off replay rules, so replaying a single request can still override a global header of the same name for that call.

When replaying a single request, XApi can override restricted headers (Cookie, Origin, Referer) that standard page scripts are blocked from setting, so replayed requests faithfully reproduce the original call.

Intercept live requests and serve custom responses without touching the backend — useful for front-end development, edge-case testing, and reproducing bugs.

• URL matching: rules match by URL prefix (startsWith) and HTTP method (GET / POST / PUT / DELETE / ANY).
• Replace mode: fully override the response with a custom status code, Content-Type, and body (JSON, text, HTML, etc.).
• JSON Patch mode: keep the original response and surgically modify specific fields via JSON paths (e.g. data.user.name, data.list[0].id). Use the ::raw:: prefix to inject numbers, booleans, null, or nested JSON.
• One-click mock from capture: right-click any captured response and choose "Mock this response" to auto-generate a rule pre-filled with the current payload.
• Per-rule toggle and global switch: enable or disable individual rules, or flip the global mock master switch. Hit counters and last-hit timestamps confirm rules are firing.

• Framework: React 19
• Styling: Tailwind CSS
• Build tool: Vite
• Language: TypeScript
• Core engine: Chrome Extensions API (Manifest V3 + declarativeNetRequest)

XApi is available on the Chrome Web Store. Search for XApi or use the link below:

• XApi - HTTP Client & API Test

1. Clone and build:

   git clone https://github.com/lustan/XApi.git
   cd XApi
   npm install
   npm run build

2. Load in Chrome:
   • Go to chrome://extensions/
   • Enable Developer mode (top right)
   • Click Load unpacked and select the dist folder.

1. Open Chrome DevTools (F12 or Ctrl+Shift+I).
2. Switch to the XApi tab.
3. Interactions on the current page appear in the Captured history.
4. Select any request to edit its body, headers, or query params, then hit Send.

1. Open the extension popup and switch to the Header tab.
2. Add a header with + Add Header, fill in the key and value, and tick its checkbox to enable it.
3. Turn on the global header switch. Every XHR/Fetch request from then on carries the enabled headers.
4. Disable a single row or flip the global switch off to stop injection at any time.

1. Open the Mock tab in the sidebar and make sure the global mock switch is on.
2. Click New Rule to define one from scratch, or right-click a captured response and pick "Mock this response" to seed a rule from the live payload.
3. Set the URL pattern (prefix match) and method, then choose a mode:
   • Replace — write the full status / Content-Type / body you want returned.
   • JSON Patch — add patch rows like data.user.name = Alice. Prefix with ::raw:: to inject non-string JSON values, e.g. ::raw::42, ::raw::true, ::raw::{"k":1}.
4. Reload the page or trigger the request — the rule's hit counter confirms it fired.

Bug reports, feature requests, and pull requests are welcome.

1. Fork the project.
2. Create your feature branch (git checkout -b feature/CoolFeature).
3. Commit your changes (git commit -m 'Add CoolFeature').
4. Push to the branch (git push origin feature/CoolFeature).
5. Open a pull request.

Distributed under the Apache 2.0 License. See LICENSE for details.