Cratesio

Crates.io Documentation CI License MSRV

MCP server for querying crates.io, the Rust package registry. Built with tower-mcp.

Gives your AI agent crate search, documentation, dependency analysis, download stats, and security auditing to make informed decisions about Rust dependencies.

Under the hood it is also a standalone, dependency-light crates.io API client library that the MCP tools are built on and that you can use directly: ~46 endpoints with full read and write coverage, no crates_io_api dependency. See Built-in crates.io client.

Quick start

Hosted (no install)

A public instance is running at https://cratesio-mcp.fly.dev/. Add to your MCP client config:

{
  "mcpServers": {
    "cratesio-mcp": {
      "type": "http",
      "url": "https://cratesio-mcp.fly.dev/"
    }
  }
}

Install from crates.io

cargo install cratesio-mcp

Build from source

git clone https://github.com/joshrotenberg/cratesio-mcp
cd cratesio-mcp
cargo install --path .

Docker

docker run -p 3000:3000 ghcr.io/joshrotenberg/cratesio-mcp:latest

MCP client configuration

Claude Code (stdio)

{
  "mcpServers": {
    "cratesio-mcp": {
      "command": "cratesio-mcp"
    }
  }
}

Claude Code (HTTP, local or remote)

{
  "mcpServers": {
    "cratesio-mcp": {
      "type": "http",
      "url": "http://localhost:3000/"
    }
  }
}

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "cratesio-mcp": {
      "command": "cratesio-mcp"
    }
  }
}

What's included

Tools (29)

Tool	Description
search_crates	Search for crates by name or keywords
get_crate_info	Detailed crate metadata (description, links, stats)
get_crate_versions	Version history with release dates and download counts
get_crate_version	Detailed metadata for a specific version
get_crate_readme	README content for a crate version
get_crate_features	Feature flags and their sub-feature activations
get_crate_docs	Browse documentation structure from docs.rs
get_doc_item	Full docs for a specific item (fn, struct, trait)
search_docs	Search for items by name within a crate's docs
get_dependencies	Dependencies for a specific version
get_reverse_dependencies	Crates that depend on a given crate
audit_dependencies	Check deps against OSV.dev vulnerability database
get_downloads	Download statistics and trends
get_version_downloads	Daily download stats for a specific version
get_crate_authors	Authors listed in Cargo.toml
get_owners	Crate owners and maintainers
get_user	User profile by GitHub username
get_user_stats	Total download stats for a user's crates
get_summary	crates.io global statistics
get_categories	Browse crates.io categories
get_category	Details for a specific category
get_keywords	Browse crates.io keywords
get_keyword	Details for a specific keyword
compare_crates	Compare two or more crates side by side (downloads, versions, dependencies, freshness)
get_dependency_tree	Full transitive dependency tree with configurable depth and deduplication markers
get_crate_health	Comprehensive health report (maturity, adoption, maintenance, security, dependency weight)
get_alternatives	Find and compare alternative crates based on keywords, downloads, and recent activity
get_crate_changelog	Changelog content from a crate's GitHub repository, optionally filtered to a version
get_release_timeline	Version-over-version registry-metadata diff: feature changes, MSRV bumps, yanked status, release cadence

Every successful tool call returns both the existing human-readable Markdown in content and typed JSON in structuredContent. Each tool advertises the matching JSON Schema 2020-12 contract through outputSchema during discovery.

Resources (3)

Resource	Description
crates://{name}/info	Crate metadata
crates://{name}/readme	Crate README content
crates://{name}/docs	Documentation structure

Prompts (6)

Prompt	Description
analyze_crate	Guided comprehensive crate analysis
compare_crates_analysis	Compare multiple crates side by side
stack_review	Evaluate a set of crates as a cohesive stack for compatibility and health
evaluate_dependencies	Evaluate a project's dependencies for health, security, and maintenance
recommend_crates	Find and evaluate crates for a given use case
migration_guide	Generate a migration guide for switching between two crates

Transports

• stdio (default): for Claude Desktop, Claude Code, and other MCP clients
• Streamable HTTP: sessionless MCP 2026-07-28 transport, while retaining compatibility with session-based MCP 2025-11-25 clients

# stdio (default)
cratesio-mcp

# HTTP
cratesio-mcp --transport http --port 3000

The HTTP transport includes a tower middleware stack: timeout, rate limiting, bulkhead concurrency control, optional response caching, and structured tracing.

The 2026-07-28 path supports server/discover, stateless requests, standardized MCP routing headers, and cache hints. Tool discovery marks every crates.io tool as read-only, non-destructive, and idempotent; resource reads advertise cache lifetimes appropriate to their data source.

Built-in crates.io client

cratesio-mcp is built on its own typed async crates.io API client, with no crates_io_api dependency. You can use it directly as a library:

• ~46 endpoints across crates, versions, owners, categories, keywords, users, teams, API tokens, publishing, and trusted publishing.
• Full read and write coverage: search and metadata, plus authenticated operations (publish, yank/unyank, add/remove owners, manage API tokens, configure trusted publishing) via .with_auth(token).
• Resilient by default: built-in rate limiting (respects the crates.io crawling policy) and retry with exponential backoff on transient failures (429 / 5xx).
• Documented and tested: every public method has doc comments, with a wiremock test suite covering the endpoints (including the authenticated write paths).

use std::time::Duration;
use cratesio_mcp::client::{CratesIoClient, CratesQuery, Sort};

let client = CratesIoClient::new("my-app", Duration::from_secs(1))?;

// Search for crates
let query = CratesQuery::builder()
    .search("tower")
    .sort(Sort::Downloads)
    .build();
let results = client.crates(query).await?;

// Get crate details
let info = client.get_crate("tower-mcp").await?;

The OSV.dev vulnerability client (audit_dependencies) and the docs.rs rustdoc-JSON client (get_crate_docs / get_doc_item / search_docs) ship alongside it.

License

MIT OR Apache-2.0