An API workspace you can git diff — and an AI can drive
API Circle is an open API client where your collections live in your own Git repo, and a built-in MCP server lets any AI client read, author, and run requests. Desktop, web, CLI, and VS Code — no cloud account, no lock-in.
$ npx @apicircle/cli mcp
Drives any Model Context Protocol client
One workspace, six superpowers
A full-featured API client in the spirit of Postman and Insomnia, with the two ideas the others miss baked into the core.
Git-backed workspaces
Your collections are plain JSON in your own repo — branch, diff, review, merge.
- Push to save, open a PR from inside the app
- Auto-created working branches off main
- Three-way merge with a visual conflict resolver
Drive your workspace with AI
A built-in MCP server exposes 94 tools so any AI client can read, author, and run requests.
- 94-tool catalog: requests, envs, mocks, plans, history
- Works with 9+ AI clients out of the box
- Copy-paste config snippet for every client
Mock any API in seconds
Point at an OpenAPI, Swagger, Postman, or Insomnia file and get a running mock on localhost.
- Import OpenAPI / Swagger / Postman / Insomnia
- Flip a 200 to a 503 to exercise error paths
- Conditional rules, validation & multipliers
17 auth schemes, all functional
Bearer to AWS SigV4 to the full OAuth2 grant set — verified against the relevant RFCs.
- OAuth2 (all grants, PKCE, device flow, refresh)
- AWS SigV4, Digest, NTLM, Hawk, JWT
- Folder-level auth that descendants inherit
A CLI for pipelines and agents
Run collections, spin up mocks, and import specs from any terminal — no UI required.
- mock · mcp · import · export · run · workspaces
- JUnit reporter for CI pipelines
- Address workspaces by name or by path
Edit the same workspace from VS Code
Nine sidebar views and YAML request editing — no webview, no separate sync.
- Nine TreeViews + YAML editing with CodeLenses
- Byte-identical commits with desktop & web
- Mock servers, secret vault & MCP host built in
Your workspace is a Git repo
Collections, environments, and mock definitions are plain JSON pushed to your own GitHub repo on a working branch. Teams collaborate the way they collaborate on code — branches, diffs, pull requests, review.
- Auto-create a working branch from
main, push to save, open a PR - A visual three-way merge resolves conflicts in the folder tree, environments, and release ledger
- Publish fingerprinted releases that linked consumers pin to — private or a public marketplace
Let an AI client drive your workspace
The bundled MCP server speaks the open Model Context Protocol over stdio. Claude, ChatGPT, Cursor, Copilot, and any other MCP client can scan a codebase, propose a collection, generate runnable code, or spin up a mock — all from the chat.
- 94-tool catalog — request & folder CRUD, environments, assertions, plans, history, mocks
- A copy-paste config snippet for every supported AI client
- Every AI write funnels through the same mutation API the UI uses — safe by construction
Mock any API in seconds
Point API Circle at an OpenAPI, Swagger, Postman, or Insomnia file and get a running HTTP mock on localhost. The Hono-based engine handles $ref dereferencing, per-endpoint overrides, conditional rules, validation, and response multipliers.
- Flip a
200to a503to exercise error paths - Mock definitions sync with the team; the runtime stays on your machine
- The same engine runs in the app, the CLI, and via the MCP
mock.starttool
Pick your surface
One engine, one workspace format, one mutation API behind all of them. Switch surfaces without switching tools.
Desktop app
Day-to-day development on Windows, macOS, and Linux — OS-keychain secrets and local mocks.
Web app
Zero install. Open the browser, and your first workspace is created automatically.
VS Code extension
Edit the same workspace as YAML, right inside your editor — no webview, no separate sync.
CLI
Run collections, spin up mocks, and import specs in CI pipelines and headless agents.
npm packages
Embed the engine, mock server, and MCP host in your own tooling.
One engine behind every surface
Every write — from the UI, the CLI, or an AI tool call — funnels through a single mutation API in the core. An AI agent can never produce state the UI couldn't have produced, and vice versa.
A workspace is JSON
Two documents — a synced collection tree and per-device runtime state. Readable, diffable, yours.
Git is the sync layer
Push the synced document to a repo on a working branch. Teammates pull, branch, and merge it like any file.
MCP is a first-class driver
The same parsers and mock engine back all surfaces, so an assistant drives exactly what you can.
Bring your APIs under version control
Open the web app in your browser, or grab the desktop build. No account, no setup — your first workspace is created the moment you arrive.