kotlin-lib-mcp

Give your AI agent the real sources of any Maven-published Kotlin/Java library.

An MCP server that, on request, downloads the sources of a library (e.g. io.ktor:ktor-client-core:3.5.1), parses them with the Kotlin Analysis API (standalone K2/FIR mode), and exposes structured information — public API surface, KDoc, dependencies/metadata, raw source + search — to MCP clients: Claude Code, Claude Desktop, IntelliJ IDEA (AI Assistant / Junie), VS Code and GitHub Copilot. An optional Compose Desktop dashboard runs the same server in-process.

Tools — fetch_library · list_packages · list_declarations · get_api_signature · get_kdoc · get_source · search_source · diff_versions · diff_api · get_dependencies · list_versions · get_latest_version — plus MCP resources and a prompt.

Those install the Docker image. For the Claude Code plugin (which runs on your JDK), IntelliJ IDEA, or to run the release zip without Docker, see Quick start.

Why this and not a docs-lookup server?

Most documentation MCP servers scrape rendered doc sites or feed the model pre-digested summaries. This one works from the published sources jar — the ground truth:

• Resolved signatures, not regex guesses. Declarations are analyzed with the same Analysis API that powers the Kotlin IDE, so get_api_signature returns real, type-resolved signatures (with graceful best-effort fallback when transitive dependencies are missing).

• KMP-aware. Kotlin Multiplatform libraries publish per-target sources jars; these are resolved properly via .module Gradle metadata, and every symbol is tagged with its targets.

• KDoc as data. Summaries, descriptions and tags are extracted per declaration — not whole HTML pages.

• Exact version you asked for, offline after the first fetch. Everything is cached on disk keyed by group/artifact/version; no re-downloads, no drift between the docs and the version you actually depend on.

• Raw source when you need it. get_source and bounded search_source let the agent read the actual implementation, not just the API.

Related MCP server: codesurface

Quick start (no build required)

Option 1 — Claude Code plugin. The server plus skills that make Claude reach for it, two commands (/kotlin-lib:api, /kotlin-lib:migrate) and a setup helper. Needs a JDK 25+ — the one on your PATH, or any other set by path in the plugin's java option; no Docker. It downloads the release zip on first use:

/plugin marketplace add aoreshkov/kotlin-lib-mcp
/plugin install kotlin-lib@kotlin-lib-mcp

See plugin/README.md for what it bundles.

Option 2 — release zip. Download the latest release, unzip (needs a Java 25+ runtime), then:

claude mcp add kotlin-lib -- /path/to/kotlin-lib-mcp-server-<version>/bin/server --transport stdio

Option 3 — Docker.

claude mcp add kotlin-lib -- docker run -i --rm -v kotlin-lib-mcp-cache:/home/mcp/.cache ghcr.io/aoreshkov/kotlin-lib-mcp

Other clients. IntelliJ IDEA, Android Studio, Junie, Claude Desktop and MCP registry installs are covered in guide/clients.md.

Tools

All tools take a Maven coordinate (group:artifact:version). Call fetch_library first — it downloads, extracts and analyzes the sources once; every other tool answers from the cached index. fetch_library, list_versions and get_latest_version also accept group:artifact, and fetch_library accepts group:artifact:latest to resolve the latest stable release.

Every tool declares a title, behavior annotations, a typed outputSchema and an icon, and returns compact JSON text with matching structuredContent. Symbols whose types can't be resolved (missing transitive dependencies) degrade to bestEffort: true PSI signatures instead of failing.

Going further

• Clients: IntelliJ IDEA, Android Studio, Junie, .mcp.json, MCP registries

• Configuration: Streamable HTTP, command-line flags, cache location

• Protocol features: tool metadata, elicitation, tasks, resources, prompt, icons

• Telemetry: OpenTelemetry traces with --otel

Privacy

Nothing about you is collected, stored remotely, or shared. There is no analytics, no phone-home, no account, and no credential of any kind.

• What leaves your machine. Only requests to the Maven repositories you point it at (Maven Central, plus any --repo; --no-maven-central drops Central): the maven-metadata.xml, .pom/.module metadata and sources jar for the coordinates you ask about. Those repositories see the coordinate and your IP, under their own privacy policies. Pulling the Docker image likewise talks to GHCR, and the Claude Code plugin's launcher talks to this repository's GitHub releases (the releases API at most once a day, and a download when there is a new server). That is the complete list of outbound traffic.

• What it reads. Downloaded library sources only. It does not read, index or transmit your project's code — it has no access to it.

• What it stores, and where. Downloaded artifacts and the parsed index, on your disk only, under the OS cache directory (see Cache) or --cache-dir. Under --tasks, task records live in a tasks/ subdirectory. Nothing is written anywhere else.

• Retention. Cached libraries stay until you delete them — the directory is browsable and safe to remove at any time. Task records are dropped once their TTL elapses (10 minutes by default, 1 hour maximum).

• Logs. stderr on your machine. --forward-logs-to-client (opt-in) mirrors them to your MCP client; --otel (opt-in) exports trace spans to the OTLP collector you configure, and carries no personal data — method names, tool names, session id, transport. Both are off by default.

• Contact. Questions: open an issue. Security or privacy reports: private vulnerability reporting.

Contributing

Contributions welcome: CONTRIBUTING.md also covers building from source. Release history lives in CHANGELOG.md, help is described in SUPPORT.md, and security reports go through private vulnerability reporting.

Sponsor

If kotlin-lib-mcp saves you time, consider sponsoring its maintenance. Sponsorship funds keeping the Analysis API version-lock current with new Kotlin releases and the supply-chain-hardened release pipeline. Every tier is appreciated.

License

Apache-2.0