Know when a pull request changes your API.
Lens reads your repository and maps every endpoint to the code behind it,
then shows what a pull request changes against your OpenAPI spec.
The API workspace is free.

API Circle is one app with two halves. The API workspace, API Circle Studio, is free and needs no account. API Circle Lens is the paid half, and it reads the code behind your API. The two are licensed and priced differently, so this page keeps them apart. apicircle.dev/pricing has the plans and what each one includes.

Lens builds a Code graph of your API from its source, every endpoint mapped to the code that implements it, and, using the Code graph and the Spec (the OpenAPI contract), identifies PR Review drift: where a pull request moves the API away from its contract.

Lens is the paid half. What it does:

• Code graph. It is built from your source, never from a spec. For each endpoint Lens records the route, the handler and the functions the handler calls, and writes the result into your repository as a codegraph/ sidecar, so it's versioned and reviewed like any other file. Where it can't read an endpoint with confidence, it reports unknown.
• PR Review drift. Lens makes two comparisons: the pull request against the Code graph of its base, and against your Spec. The findings are concrete: a route removed, access control dropped, a status the Spec doesn't document. In the desktop app, nothing reaches your Git host until you press Submit.
• Languages. TypeScript and JavaScript, Python, Go, Java, C# and Rust. The Code graph page lists the frameworks for each. PHP is read only by pattern matching on route lines, and Ruby, Elixir and Kotlin aren't supported yet.
• Git hosts. GitHub works on every plan, including free. Lens speaks GitLab, Bitbucket Cloud and Azure DevOps through each host's own review API, and those three are a paid capability.
• Your code stays on your machine. Analysis runs locally and sends API Circle no repository content. The one exception is "Index with AI", an optional pass that asks first and sends the files it reads to the AI provider you chose, with your own key.

Lens desktop holds the whole workspace plus the Code graph, Review, Assistant and MCP panels, and the workspace inside it stays free. Download it from the latest release.

The Lens installers aren't code-signed yet, so your system asks before the first run. On Windows, SmartScreen warns: choose More info → Run anyway. On macOS, open System Settings → Privacy & Security and choose Open Anyway. On Linux, install the .deb, or make the AppImage executable and run it. The release page has the full steps. Signed builds are in progress.

@apicircle-lens/cli installs the apicircle-lens binary. It runs the same drift check in CI and exits with a code your pipeline can stop on. The MCP server ships inside it.

npm install -g @apicircle-lens/cli
export APICIRCLE_LENS_CLI_KEY="<your key>"

apicircle-lens codegraph index                          # build the Code graph, then commit the folder it writes
apicircle-lens review --base base.json --openapi openapi.yaml --fail-on breaking
apicircle-lens mcp --repo /absolute/path/to/your/repo   # the Lens MCP server, over stdio

base.json is the Code graph committed on your base branch. The documentation shows the git show line that produces it.

Before you start, you need:

• Node.js 20 or later.
• An API Circle account on a plan that includes the CLI. apicircle-lens mcp needs a plan that includes the MCP server. Compare plans.
• A CLI key. Sign in at account.apicircle.dev, open CLI keys, create a key and put it in APICIRCLE_LENS_CLI_KEY. In CI, store it as a secret.

The Lens CLI documentation has a walkthrough of one pull request, every finding the review can raise, a reference for each command, and a complete pipeline file for GitHub Actions, GitLab CI/CD, Bitbucket Pipelines, Azure Pipelines and CircleCI.

Two more things live in this binary and therefore need a CLI key. apicircle-lens run runs a saved execution plan headlessly, and apicircle-lens mock serves a mock from a spec file. Inside the free apps, both are free.

The MCP server gives an AI client your Code graph and PR Review. The desktop app's MCP panel installs it into Claude Desktop, Claude Code, Codex, Cursor, Continue, Zed and Windsurf, and any other MCP client takes a pasted snippet. HAR import (import.har) and code generation (generate.code) are tools of this MCP server. The free workspace has neither.

Moving from @apicircle/cli or @apicircle/mcp-server? Both are deprecated. apicircle <command> is now apicircle-lens <command>, apicircle-mcp is now apicircle-lens mcp, and both need a CLI key.

Your API workspace is just code. Store it like code and review it like code. Studio is the API client built on that: free, no account, and developed in the open at apicircle/studio.

• A workspace is a Git repository. Collections, environments and mock definitions are plain JSON that Studio pushes to a working branch in your own GitHub repository. It opens the pull request from inside the app, and walks you through a three-way merge when two people changed the same thing. Auth credentials are blanked before every push. Run history and sessions stay on the device.
• Requests. Seven HTTP methods and eight body types, GraphQL among them. It speaks HTTP only: no WebSocket, SSE, gRPC or scripts.
• Authentication. 15 schemes: Bearer, Basic, API key, custom header, six OAuth 2.0 grants (with PKCE, device code and token refresh), AWS Signature v4, Digest, NTLM, Hawk and JWT Bearer. A folder can carry auth that its requests inherit. Signing is checked against RFC and NIST reference vectors.
• Environments and secrets. Environments stack in priority order. Secrets live in the Secret Vault, encrypted with AES-256-GCM, and on the desktop the operating system's keychain wraps the key.
• Mock servers. Give Studio an OpenAPI, Swagger, Postman or Insomnia file and it serves a mock on 127.0.0.1, with response rules, request validation, delays and multipliers. Studio desktop and the VS Code extension run mocks. The web app edits mock definitions but can't run one, because a browser tab can't listen on a port.
• Execution plans and assertions. Chain saved requests, pass a value extracted from one response into the next request, and grade each response with five kinds of assertion. Plans run in the app for free. Running one headlessly in CI is the Lens command line.
• Imports. OpenAPI / Swagger, Postman v2.1 collections, Postman environments, Insomnia v4 exports, cURL commands and API Circle exchange files.
• History and snapshots. Every request and plan you run is kept on the device with its headers, body and assertion results. Studio also snapshots the workspace before a push, a merge or an import.

The workspace engine and the mock engine are also on npm, as @apicircle/shared, @apicircle/core and @apicircle/mock-server-core, under the Studio licence below.

• Own your data. A workspace you can cat, diff, and git log is a workspace nobody can hold hostage.
• Git is the sync layer. Branches and pull requests already solved collaboration. We didn't need to reinvent that.

• ⭐ Star studio to follow the free workspace
• 🐛 File workspace bugs and ideas in issues
• ✉️ Ask about Lens, a plan or a licence at apicircle.dev/contact
• 🔒 Report a vulnerability through apicircle.dev/security

Licences. API Circle Studio is released under a custom source-available licence: free for personal, educational, and non-commercial use (plus a 30-day commercial evaluation). It is not an OSI-approved open-source licence; ongoing commercial use requires a separate licence. See LICENSE. API Circle Lens, @apicircle-lens/cli included, is proprietary, and the Terms of Service govern its use.

_{apicircle.dev · Pricing · Download · Docs}