Kernel API Tester
A free HTTP client for VS Code — collections, environment variables, and Postman import, without leaving your editor. It's the API Tester tool from Kernel DevTools (our browser extension), ported to run as its own standalone thing.
Install from VS Code MarketplaceWhat it is
Kernel DevTools is a browser extension with 30+ tools that plug into your browser's built-in DevTools panel — Console, Network Inspector, DOM Tree, Mock API, and so on. Most of those tools only make sense inside a browser, because they work by inspecting a live webpage: reading its console output, intercepting its network traffic, walking its DOM tree. There's no browser tab to inspect inside a code editor, so none of that can come along.
The API Tester is different. It's just an HTTP client — you type a URL, pick a method, set headers and a body, and it sends the request and shows you the response. That doesn't depend on a browser at all, so it's ported here as a standalone VS Code extension: a sidebar panel with the same request/response UI, collections, and environment variables as the browser version.
Features
Saved collections
Group requests into named collections, exactly like the browser extension's API Tester — reload any saved request with one click.
How it differs from the browser extension
Most of the request/response logic is identical — same UI, same data model, collections and environment variables round-trip between the two if you export/import. Two deliberate differences:
- No SSRF/private-IP blocking. The browser extension's API Tester blocks requests to
localhostand private IP ranges, because a malicious webpage could otherwise abuse the extension's elevated permissions to probe your internal network. That threat doesn't exist in an editor — every request is one you typed yourself — and testing a local dev server is a core use case here, so that restriction is removed. - Storage. The browser version uses
chrome.storage.local; this one uses VS Code's ownglobalStateAPI. Collections don't sync between the two automatically, but the export/import JSON format is compatible.
Installing
It's live on the VS Code Marketplace — install it directly, or from inside VS Code: open the Extensions panel (Ctrl+Shift+X), search "Kernel API Tester", and click Install.
How it compares
| Tool | Strengths | Trade-offs |
|---|---|---|
| Kernel API Tester | Free, no account, collections + env vars + Postman import, VS Code sidebar panel | No GraphQL-specific UI, no gRPC support (yet) |
| Thunder Client | Free tier + paid Pro, similar collection/env model, editor-tab based | Sync and some features are paid; closed source |
| Postman (VS Code extension) | Full Postman feature set, cloud sync, team workspaces | Requires a Postman account; heavier, more setup |
| REST Client (.http files) | Plain text files, git-friendly, no UI to learn | No visual collections browser, no built-in env-variable UI |
Frequently asked questions
Feedback & support
Found a bug or have a feature request? Report an issue, or email privacy@kerneltools.dev — the same address the browser extension uses for support.