kotlin-lib-mcp — browse the sources, API and KDoc of any Maven-published Kotlin/Java library

[aoreshkov]

kotlin-lib-mcp gives MCP clients direct access to the real sources of any Maven-published Kotlin/Java library, so an assistant can answer API questions from the actual code instead of guessing from training data.

Point it at a coordinate — io.ktor:ktor-client-core:3.5.1, or just group:artifact for the latest stable — and it downloads the sources jar, parses it with the Kotlin Analysis API (K2 standalone), and serves structured results from an on-disk cache.

GitHub (demo GIF in the README): https://github.com/aoreshkov/kotlin-lib-mcp
Registry: io.github.aoreshkov/kotlin-lib-mcp

What it exposes

• 10 tools: fetch_library, list_packages, list_declarations, get_api_signature, get_kdoc, get_source, search_source, get_dependencies, list_versions, get_latest_version
• Resources: every cached library index, plus a resource template kotlinlib://{group}/{artifact}/{version}/index
• Prompt: explain_public_api(coordinate, package?)
• Transports: stdio and Streamable HTTP

MCP details I tried to get right

• Every tool declares a title, behavior annotations (readOnlyHint, openWorldHint, destructiveHint, idempotentHint) and an outputSchema derived from its response DTO — results carry both JSON text and matching structuredContent.
• The server advertises the logging capability and mirrors its internal logs to clients as notifications/message, honoring each session's logging/setLevel — handy on stdio, where clients routinely discard stderr.
• fetch_library emits progress notifications (download → analyze → cache) when the request carries a progressToken.
• The HTTP transport keeps the SDK's localhost-only DNS-rebinding defaults, extendable with repeatable --allowed-host / --allowed-origin flags.
• Release artifacts (zip + Docker image) ship with SLSA build-provenance attestations, verifiable via gh attestation verify.

Install

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

Or grab the zip from the releases page (needs Java 21+). There's also an optional Compose Desktop dashboard that embeds the server in-process (control, logs, cache browser).

Built with the Kotlin MCP SDK (kotlin-sdk-server 0.14). Feedback very welcome — especially from anyone pointing it at unusual KMP library setups, since per-target sources-jar resolution via .module Gradle metadata was the trickiest part.