quasar-mcp

quasar-mcp is an MCP server that gives LLM clients such as Claude Code, Claude Desktop, Codex and Cursor the research tools of Quasar, an AI research assistant for astronomy archive workflows. It serves about 200 tools, all working on live data:

Plots and images are returned as MCP image content, so clients that display images show them inline. The full reference for every tool and its parameters is in docs/TOOLS.md.

Installation

Python 3.12 or later. The recommended way is uv, which runs the server in its own environment without a separate install step:

uvx --from git+https://github.com/adamzacharia/quasar-mcp quasar-mcp --list

The first run installs the scientific Python stack (astropy, astroquery, pyvo and friends) and takes a few minutes; later starts take 10 to 25 seconds. Run that command once in a terminal before adding the server to a client with a short startup timeout. It prints the tool list when it is ready.

Or install it with pip into an environment of your choice:

pip install git+https://github.com/adamzacharia/quasar-mcp
quasar-mcp --list

Related MCP server: aqc-mcp

Connect a client

Claude Code

claude mcp add quasar -- uvx --from git+https://github.com/adamzacharia/quasar-mcp quasar-mcp

Claude Desktop (Settings > Developer > Edit Config), Cursor (~/.cursor/mcp.json) or any client with a JSON config:

{
  "mcpServers": {
    "quasar": {
      "command": "uvx",
      "args": ["--from", "git+https://github.com/adamzacharia/quasar-mcp", "quasar-mcp"]
    }
  }
}

Codex (~/.codex/config.toml):

[mcp_servers.quasar]
command = "uvx"
args = ["--from", "git+https://github.com/adamzacharia/quasar-mcp", "quasar-mcp"]

If you installed with pip, use quasar-mcp as the command with no arguments.

Then ask, for example:

• Which ALMA Band 7 observations of TW Hya have resolution better than 0.1 arcsec?

• What lines lie within 50 MHz of CO 3-2?

• Give me the BibTeX for the DSHARP overview paper.

• Make a finding chart for HL Tau and list Gaia DR3 stars within 1 arcmin.

Serving a subset

Every tool description is sent to the model. Clients that load all tools up front can be given a subset:

quasar-mcp --categories archive,literature

Categories: general (ALMA archive, lines, MAST/ESO/CADC, web), archive (archives, catalogues, VO), literature, datalab, analysis, mmu_hats. Claude Code loads tool descriptions on demand, so it does not need this.

Configuration

Most tools use public services and need no configuration. API keys for the rest are read from environment variables or from ~/.quasar-mcp/.env (copy .env.example there); a real environment variable wins over the file.

A tool whose key is missing returns an error that names the variable; every other tool keeps working. Keys can also be passed in the client config:

"quasar": {"command": "uvx", "args": ["--from", "git+https://github.com/adamzacharia/quasar-mcp", "quasar-mcp"],
           "env": {"NASA_ADS_API_KEY": "your-token"}}

Shared HTTP server

quasar-mcp --http 8765                 # streamable HTTP at http://127.0.0.1:8765/mcp
claude mcp add --transport http quasar http://127.0.0.1:8765/mcp

The HTTP server has no authentication, spends the API keys it was started with, and can download files to its machine. Keep the default 127.0.0.1 binding and put an authenticating proxy or VPN in front before sharing it. All HTTP clients share one session.

Behaviour worth knowing

• Tools can build on the previous search. filter_results, check_line_coverage, check_co_lines, plot_alma_results and get_mast_products work on the last archive search in the same session.

• Results carry their provenance. Archive tools report the query or ADQL they ran and the service they hit, and every tool has a time budget; a slow or failed service returns a structured error naming the host instead of hanging. Models usually recover with another tool (for example resolve_target falls back from SIMBAD to Sesame).

• No invented data. When a service or key is unavailable the tool says so; it never substitutes examples.

• Downloads go to the machine running the server: ALMA products under ~/.quasar-mcp/downloads/, MAST products under ~/quasar_data/mast/.

• Not included from Quasar: the chat app, web interface, accounts and the server-side browser tools.

Tested

Before each release the server is started as a real MCP client would start it and driven by language models on realistic questions (ALMA archive counts, line identification, BibTeX, the GWOSC catalogue, sensitivity), with every number checked against the tool's own output. For 0.1.0, on a fresh install:

Development

git clone https://github.com/adamzacharia/quasar-mcp
cd quasar-mcp
python -m venv .venv && . .venv/bin/activate     # Windows: .venv\Scripts\activate
pip install -e ".[test]"
pytest                                            # unit tests + a full server start
python scripts/gen_tools_doc.py                   # regenerate docs/TOOLS.md

The tools themselves are developed in the Quasar repository. src/quasar_mcp/_vendor/ is a copy of Quasar's backend, refreshed with python scripts/sync_from_quasar.py /path/to/Quasar (it scans the copy for keys and local paths before finishing); UPSTREAM.md records the Quasar commit. Report tool bugs and requests in issues.

Related

• alma-mcp: MCP servers with methods, settings and recipes from about 3,500 ALMA papers, plus tested analysis tools (dust masses, line luminosities, kinematics, uv fitting). It pairs with this server: alma-mcp says how published papers did a step, quasar-mcp fetches the data to do it.

License

PolyForm Noncommercial 1.0.0: free for research, teaching and other noncommercial use. The ALMA guidance reference in src/quasar_mcp/_vendor/third_party/alma-data-skill/ is included with its author's permission (see its UPSTREAM.json).