Xhelio Cdaweb

NASA CDAWeb data access for heliophysics — browse observatories, inspect parameters, fetch CDF data.

Works as a standalone Python library or as an MCP server for any MCP-compatible LLM client (Claude Desktop, Cursor, custom agents).

What's included

• 65 observatory catalogs with 2900+ datasets — ACE, Parker Solar Probe, Solar Orbiter, Wind, MMS, THEMIS, GOES, Voyager, and more
• 2880 pre-built parameter metadata files from Master CDF skeletons — browse_parameters works instantly, no network required
• Automatic data validation — fetched CDF files are compared against Master CDF metadata to detect phantom (documented but missing) and undocumented (present but undocumented) parameters
• Structured system prompts per observatory — give an LLM full context about available instruments, datasets, and time coverage

Observatory catalogs are built directly from the CDAWeb REST API observatory groups — no hand-curated mappings.

Installation

# Library only
pip install xhelio-cdaweb

# With MCP server
pip install xhelio-cdaweb[mcp]

MCP Server

Configuration (Claude Desktop, Cursor, etc.)

{
  "mcpServers": {
    "cdaweb": {
      "command": "xhelio-cdaweb-mcp"
    }
  }
}

With custom cache directory:

{
  "mcpServers": {
    "cdaweb": {
      "command": "xhelio-cdaweb-mcp",
      "args": ["--cache-dir", "/path/to/cache"]
    }
  }
}

Or run directly:

xhelio-cdaweb-mcp
xhelio-cdaweb-mcp --cache-dir /path/to/cache
python -m cdawebmcp

Cache directory

All runtime data is stored under a single root directory. Defaults to ~/.cdawebmcp/.

On first use, bundled data (observatory catalogs and parameter metadata) is copied into the cache directory. This ensures all reads and writes happen in one writable location, even for non-editable installs from PyPI.

Configure via --cache-dir (MCP server), the XHELIO_CDAWEB_CACHE_DIR environment variable, or cdawebmcp.configure() (library):

XHELIO_CDAWEB_CACHE_DIR=/path/to/cache xhelio-cdaweb-mcp

import cdawebmcp
cdawebmcp.configure(cache_dir="/path/to/cache")

~/.cdawebmcp/                  # or custom path via configure()
├── observatories/                  # Observatory catalog JSONs (bootstrapped from package)
├── metadata/                  # Parameter metadata JSONs (bootstrapped from package)
├── cdf_cache/                 # Downloaded CDF data files (permanent, reused across fetches)
│   └── ace/mfi/               #   organized by observatory/instrument path
│       └── ac_h2_mfi_2024.cdf
└── overrides/                 # Validation sync results (append-only)
    └── ace/
        └── AC_H2_MFI.json

• observatories/ — Observatory catalog JSONs. Bootstrapped from bundled package data on first use.
• metadata/ — Parameter metadata JSONs. Bootstrapped from bundled package data on first use. New metadata is fetched on demand from Master CDFs.
• cdf_cache/ — Permanent cache of downloaded CDF files. Once a CDF file is downloaded, it is never re-downloaded. Use manage_cache(action="clean", category="cdf_cache") to free disk space.
• overrides/ — Validation results from comparing fetched data against metadata. Append-only, one JSON per dataset.

Tools

Tool	Description
browse_observatories()	List all 65 CDAWeb observatories with descriptions, dataset counts, and instruments
load_observatory(observatory_id)	Get the complete system prompt for an observatory (role instructions + full dataset catalog)
browse_parameters(dataset_id)	Browse all variables in a dataset — name, type, units, description, plus validation status if available
fetch_data(dataset_id, parameters, start, stop, output_dir)	Download CDF data, write to file, return metadata + per-column stats (min, max, mean, std, nan_ratio)
manage_cache(action, ...)	Cache management — status, clean, refresh metadata, refresh time ranges, rebuild catalog

Typical workflow

browse_observatories  →  load_observatory("ace")  →  browse_parameters("AC_H2_MFI")  →  fetch_data(...)

1. Discover available observatories
2. Load an observatory's full catalog and instructions
3. Inspect dataset parameters to choose what to fetch
4. Fetch data for a time range — returns file path + statistics

Python Library

from cdawebmcp.catalog import browse_observatories
from cdawebmcp.prompts import build_observatory_prompt
from cdawebmcp.metadata import browse_parameters
from cdawebmcp.fetch import fetch_data

# List all 65 observatories
observatories = browse_observatories()

# Get observatory-specific system prompt
prompt = build_observatory_prompt("ace")

# Browse dataset parameters (instant — uses bundled metadata)
params = browse_parameters(dataset_id="AC_H2_MFI")

# Fetch data — returns DataFrames directly
result = fetch_data("AC_H2_MFI", ["Magnitude"], "2024-01-01", "2024-01-02")
mag = result["Magnitude"]
print(mag["data"])       # pandas DataFrame
print(mag["units"])      # "nT"
print(mag["stats"])      # per-column {min, max, mean, std, nan_ratio}

Data validation

When fetch_data downloads CDF files, it automatically compares actual data variables against the bundled Master CDF metadata. Discrepancies are recorded in ~/.cdawebmcp/overrides/ and surfaced through browse_parameters:

• Phantom parameters — listed in metadata but absent from actual data files
• Undocumented parameters — present in data files but not in official metadata

This validation runs once per unique CDF source URL and builds an append-only archive with full provenance (source file, URL, timestamp).

Bundled data

Data	Count	Description
Observatory catalogs	65	Instruments, datasets, time coverage, PI info
Parameter metadata	2880	Variable names, types, units, fill values, sizes
Prompt templates	2	Generic role + CDAWeb-specific workflow instructions

All bundled data ships with the package and is copied to the cache directory on first use. No network access needed for browsing — only fetch_data requires a connection to CDAWeb.

Catalog updates

Rebuild from CDAWeb REST API:

# Rebuild observatory catalogs (uses CDAWeb observatory groups API)
python -m cdawebmcp.scripts.build_catalog
python -m cdawebmcp.scripts.build_catalog --observatory ace
python -m cdawebmcp.scripts.build_catalog --list

# Rebuild parameter metadata from Master CDFs
python -m cdawebmcp.scripts.build_metadata
python -m cdawebmcp.scripts.build_metadata --observatory psp

Development

pip install -e ".[dev]"
pytest tests/ -v

For a CI-safe MCP check that does not fetch CDAWeb data, run:

uv run --extra mcp python scripts/smoke_mcp_list_tools.py --json

The smoke starts the stdio server with an isolated temporary cache, runs MCP initialize + list_tools, and verifies the advertised tool names.

MCP registry manifest

This repository includes server.json for MCP registry publishing. Keep its version in sync with pyproject.toml and src/cdawebmcp/__init__.py.

License

MIT