VS Code Extension

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 Marketplace

What 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 collectionsGroup requests into named collections, exactly like the browser extension's API Tester — reload any saved request with one click.
Environment variablesDefine {{variableName}} placeholders once and reuse them across any URL, header, or request body. Toggle variables on/off without deleting them.
Postman v2.1 importPaste a Postman Collection v2.1 export (or Kernel's own JSON format) and it's parsed into collections and requests automatically.
Export to fileExport a single collection or all of them to a .json file via VS Code's native save dialog — for backup, version control, or sharing with teammates.
Save example responsesOptionally attach the last response (status, headers, body, timing) to a saved request, so reloading it later shows a worked example without re-sending.
Full method supportGET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS, and QUERY (the newer IETF-drafted method for safe requests that need a body).

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 localhost and 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 own globalState API. Collections don't sync between the two automatically, but the export/import JSON format is compatible.
Note: this is a genuinely separate extension with its own install and its own settings — installing the browser extension doesn't give you this, and vice versa.

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

ToolStrengthsTrade-offs
Kernel API TesterFree, no account, collections + env vars + Postman import, VS Code sidebar panelNo GraphQL-specific UI, no gRPC support (yet)
Thunder ClientFree tier + paid Pro, similar collection/env model, editor-tab basedSync and some features are paid; closed source
Postman (VS Code extension)Full Postman feature set, cloud sync, team workspacesRequires a Postman account; heavier, more setup
REST Client (.http files)Plain text files, git-friendly, no UI to learnNo 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 [email protected] — the same address the browser extension uses for support.