kegg-mcp-server-python

An unofficial Python Model Context Protocol (MCP) server for the KEGG bioinformatics database. It exposes 34 tools, 9 resource templates, and 4 guided prompts to any MCP-compatible client (Claude Desktop, Claude Code, Cursor, etc.). Developed by Elytron Biotech.

Built on the official MCP Python SDK v2 (MCPServer), returns structured Pydantic JSON (not raw text), and includes per-operation TTL caching, request retry with exponential backoff, a three-request-per-second rate limit, structured JSON stderr logging, and batch helpers out of the box. No API key is required.

Responses are token-aware by default: get_*_info tools return a compact EntrySummary (entry id, name, class, description, counts of linked entities) unless you pass detail_level="full". List- and mapping-shaped outputs are capped at 100 items and report the full count plus truncated. Failures are MCP tool errors (isError: true) whose text is a typed ErrorResult JSON (code, retryable, hint) the model can reason about.

0.5.0 changes output shapes: failures (including not-found) are now isError: true instead of a normal result; convert_identifiers maps each source ID to a list of targets; link/ortholog/pathway-gene/DDI outputs are capped with truncated; batch_entry_lookup returns summaries unless detail_level="full"; logging is configured with --log-level / --log-tracebacks instead of environment variables.

Usage notice: This is a community project and is not affiliated with or endorsed by KEGG or Kanehisa Laboratories. KEGG states that its REST API is for academic use by academic users; non-academic users must follow KEGG's linked non-academic-use guidance. Users are responsible for ensuring that their use complies with those terms.

Quick start

With uvx (no install)

uvx kegg-mcp-server

With pip

pip install kegg-mcp-server
kegg-mcp-server

Requires the MCP Python SDK v2 (mcp>=2,<3, protocol revision 2026-07-28). Versions up to 0.3.1 ran on the 1.x SDK; because mcp 2.0 removed mcp.server.fastmcp, that is a breaking dependency change, which is why this is 0.4.0 rather than a patch. Nothing changes for clients — an mcp 2.x server answers every earlier protocol revision from the same app, so a host still on the 1.x SDK connects unchanged and negotiates 2025-11-25.

Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "kegg": {
      "command": "uvx",
      "args": ["kegg-mcp-server"]
    }
  }
}

Claude Code

claude mcp add kegg-mcp-server -- uvx kegg-mcp-server

Or install as a plugin (includes slash commands, agent, and skill):

claude plugin marketplace add Lucas-Servi/kegg-mcp-server-python
claude plugin install kegg-mcp-server@kegg-mcp-server

Or, in one step (Claude Code v2.1.292+), pointing install at the marketplace directly:

claude plugin install kegg-mcp-server --marketplace Lucas-Servi/kegg-mcp-server-python

The plugin starts a local (stdio) MCP server, so it works in Claude Code, Cowork, and Claude Desktop, but not in the claude.ai web app.

The plugin bundles:

MCPB bundle (Linux x86-64 only, no Python install required)

The release bundle is built specifically for Linux x86-64 and CPython 3.12 because it vendors native dependencies. Download the linux-x86_64-py312.mcpb artifact from the releases page and drag it onto Claude Desktop. On macOS or Windows, use the cross-platform uvx, pip, or Claude Code plugin installation above.

What's included

34 Tools

9 Resource Templates

Direct URI-based access to KEGG entities:

kegg://pathway/{pathway_id}        e.g. kegg://pathway/hsa00010
kegg://gene/{gene_id}              e.g. kegg://gene/hsa:1956
kegg://compound/{compound_id}      e.g. kegg://compound/C00002
kegg://reaction/{reaction_id}      e.g. kegg://reaction/R00756
kegg://disease/{disease_id}        e.g. kegg://disease/H00004
kegg://drug/{drug_id}              e.g. kegg://drug/D00001
kegg://organism/{org_code}         e.g. kegg://organism/hsa
kegg://pathway/{pathway_id}/ascii  e.g. kegg://pathway/hsa00010/ascii
kegg://search/{database}/{query}   e.g. kegg://search/compound/glucose

4 Guided Prompts

ASCII Pathway Renderer

The render_pathway_ascii tool converts KEGG pathway topology (from KGML XML) into LLM-friendly ASCII text. Two styles are available:

Chain mode (default) — linear reaction flow:

Glycolysis / Gluconeogenesis (hsa)
====================================

[alpha-D-Gl~] ──R01786──▶ [beta-D-Gl~] ──R01600──▶ [beta-D-F~]

Grid mode — 2D spatial layout using KGML coordinates:

Glycolysis / Gluconeogenesis (hsa)
====================================

  [Glc]────────▶[G6P]────────▶[F6P]
                  │
                  ▼
                [6PG]

Legend:
  [Glc] = alpha-D-Glucose (cpd:C00267)
  [G6P] = D-Glucose 6-phosphate (cpd:C00092)

Transport options

# stdio (default -- for Claude Desktop, Claude Code, uvx)
kegg-mcp-server

# Streamable HTTP (for web/API deployment)
kegg-mcp-server --transport streamable-http --host 0.0.0.0 --port 8080

# python -m also works
python -m kegg_mcp_server

# Logging (stderr, JSON): verbosity and full tracebacks
kegg-mcp-server --log-level DEBUG --log-tracebacks

Data handling

• The only network destination is the public KEGG REST API at https://rest.kegg.jp (all tools, resources, and the ASCII renderer's KGML fetch go there). Queries you make (IDs, search terms) are sent to KEGG; nothing is sent anywhere else, and there is no telemetry.
• Responses are cached in memory only (per-operation TTL) and discarded when the server exits; nothing is written to disk.
• Logs are structured JSON on stderr only, on your machine.
• No API key or account, and the server reads no environment variables of its own (logging is set by CLI flags). The HTTP client (httpx) honours the standard proxy and CA-bundle variables (HTTPS_PROXY, NO_PROXY, SSL_CERT_FILE, …) so it works behind corporate proxies.
• The uvx launcher downloads the pinned kegg-mcp-server package and its dependencies from PyPI on first run.

Development

git clone https://github.com/Lucas-Servi/kegg-mcp-server-python
cd kegg-mcp-server-python
pip install -e ".[dev]"

# Run tests
pytest tests/ -v

# Lint
ruff check src/ tests/

# Debug with MCP Inspector
mcp dev kegg-mcp-server

Project structure

src/kegg_mcp_server/
  server.py       MCPServer instance, lifespan (httpx client + TTL cache), CLI
  client.py       KEGGClient: async KEGG REST with retry/backoff + KEGG-politeness semaphore
  cache.py        Per-op TTL cache, 64 MiB budget (info 24h, list 1h, entry ops 6h)
  parsers.py      KEGG flat-file and tab-delimited response parsers + summarize_flat_entry
  errors.py       KEGGAPIError exception type
  logging.py      JSON stderr logger (stdout is reserved for MCP stdio framing)
  resources.py    9 MCP resource templates
  prompts.py      4 bioinformatics workflow prompts
  models/         Pydantic models for all KEGG entity types + EntrySummary + ErrorResult
  tools/          13 tool modules, each with a register(mcp) function; _common.py has the
                  @kegg_tool error-boundary decorator and shared READ_ONLY annotations

Author

Developed by Lucas Servi (lucasservi@gmail.com) at Elytron Biotech using Claude Code.

Acknowledgments

• Based on Augmented-Nature/KEGG-MCP-Server -- the original TypeScript implementation that served as the foundation for this Python rewrite
• KEGG -- Kyoto Encyclopedia of Genes and Genomes (Kanehisa Laboratories)
• Model Context Protocol -- Anthropic's open protocol for LLM tool use

License

MIT -- see LICENSE.