gsa-perdiem-mcp

MCP server for the GSA Per Diem Rates API. Federal travel lodging and M&IE rates for IGCEs and travel cost estimation.

Works without configuration using DEMO_KEY. Optional free API key for higher rate limits.

Tested and hardened through six rounds of integration testing against the live GSA Per Diem API, including a round-6 live audit with a real api.data.gov key. 413 regression tests covering 1 P0 path-traversal bug, 23 P1 silent-wrong-data bugs, and 21 P2 validation gaps fixed. See TESTING.md for the full testing record.

What it does

Exposes the GSA Per Diem API as 6 MCP tools:

Core lookups

• lookup_city_perdiem - Rates by city/state (auto-selects best NSA match)
• lookup_zip_perdiem - Rates by ZIP code
• lookup_state_rates - All NSA rates for a state
• get_mie_breakdown - M&IE tier table (meal components)

Workflow

• estimate_travel_cost - Calculate trip per diem (lodging + M&IE with first/last day at 75%)
• compare_locations - Compare rates across multiple cities

Get your own API key (strongly recommended)

This server hits api.gsa.gov, which uses api.data.gov for rate limiting.

• Without a key: falls back to the shared DEMO_KEY which is capped at ~10 requests per hour across everyone using it. A couple real prompts will blow through that limit and you'll start seeing 429 errors.
• With a personal key: 1,000 requests per hour, yours alone.

Get a free key (takes 30 seconds):

1. Go to api.data.gov/signup
2. Enter your name and email — no approval, no wait
3. Copy the key from the confirmation page
4. Paste it into your Claude Desktop config as PERDIEM_API_KEY (see below)

The same key works for every api.data.gov-backed API (GSA Per Diem, NASA, FEC, FCC, etc.).

Installation

uvx gsa-perdiem-mcp

Claude Desktop configuration

Recommended (with your own key):

{
  "mcpServers": {
    "gsa-perdiem": {
      "command": "uvx",
      "args": ["gsa-perdiem-mcp"],
      "env": {
        "PERDIEM_API_KEY": "paste-your-api-data-gov-key-here"
      }
    }
  }
}

Without a key (works for a handful of calls per hour, then 429s until the hour rolls over):

{
  "mcpServers": {
    "gsa-perdiem": {
      "command": "uvx",
      "args": ["gsa-perdiem-mcp"]
    }
  }
}

Example prompts

• "What's the per diem rate for Washington DC in FY2026?"
• "Estimate travel costs for 4 nights in Boston in March."
• "Compare per diem rates for DC, New York, and San Francisco."
• "What are all the NSA per diem locations in Virginia?"
• "Show me the M&IE meal breakdown for the $92 tier."
• "Build a travel estimate: 3 trips to Seattle (4 nights each) and 2 trips to DC (3 nights each)."

Important: maximum reimbursement, not actual prices

Per diem rates are federal reimbursement ceilings per 41 CFR 301-11. They are not actual hotel prices. CONUS only. OCONUS rates are from the State Department. Lodging taxes generally not included. First/last travel day M&IE at 75%.

Companion tools

Use alongside bls-oews-mcp (wage data) and gsa-calc-mcp (ceiling rates) for complete IGCE development. Per diem covers the travel component; BLS and CALC+ cover labor.

License

MIT