gsa-perdiem-mcp

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

ZIP, state, and M&IE lookups for FY2021 onward work with no key and no network call: they are answered from GSA's published rate, ZIP, and M&IE files bundled in the package. City lookups use the GSA Per Diem API, which resolves city names to rate areas; they work with the shared DEMO_KEY, and a free API key raises the limit. Use the installation and configuration instructions below to connect this MCP directly.

Tested and hardened through seven rounds of integration testing against the live GSA Per Diem API, including a round-7 independent re-audit with live verification. 542 collected regression tests (275 offline, 267 live-gated) covering 1 P0 path-traversal bug, 23 P1 silent-wrong-data bugs, 21 P2 validation gaps, 14 round-7 findings, and the 1.1.0 rate-area ambiguity fixes. See testing.md for the full testing record.

Available in Claude and ChatGPT

A hosted edition is running at https://gsa-perdiem.1102tools.com/mcp and is planned for the Claude and ChatGPT directories. It needs no user API key and no local setup. Locally, a free personal key is recommended; a shared fallback works at low volume. Until the listings are live, use the installation and configuration instructions below, then try a matching prompt.

What it does

Exposes GSA per diem rates as 7 MCP tools:

Core lookups

• lookup_city_perdiem - Rates by city/state, resolved through the GSA API (optional county answers from GSA's county definitions without an API call)
• lookup_zip_perdiem - Rates by ZIP code from GSA's ZIP file (optional county)
• lookup_state_rates - All NSA rates and the standard rate for a state
• get_mie_breakdown - M&IE tier table (meal components)
• get_data_status - Bundled fiscal years, their GSA source files, and which tools call the API

Workflow

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

Rate areas are never guessed. GSA sets rates by county or locality. When a ZIP or city spans more than one rate area with different rates, results have status: "ambiguous" and list every candidate; supplying county selects one. A city GSA does not recognize is unresolved rather than defaulting to the standard rate. When GSA lists several rate areas for a city, Census 2020 place-to-county records break the tie only if they place the city in exactly one of them. Every result names its source: the bundled GSA file (with SHA-256) or the API endpoint.

Bundled data. src/gsa_perdiem_mcp/data/ holds FY2021 onward, generated by scripts/build_snapshot.py from GSA's per diem files page and Census 2020 place/county code files. data/manifest.json records each source URL and SHA-256. The builder fails on schema drift, on any disagreement between GSA's rate and ZIP files, and on locality wording it has not been taught. FY2020 and fiscal years not yet bundled use the API.

Get your own API key (strongly recommended)

City lookups hit api.gsa.gov, which uses api.data.gov for rate limiting. ZIP, state, and M&IE lookups for bundled fiscal years need no key.

• Without a key: city lookups fall back to the shared DEMO_KEY, which is capped at ~10 requests per hour across everyone using it. City-heavy prompts can exhaust that limit and return 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 client 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

Configuration

Use the configuration below as the server definition and adapt its placement to your compatible MCP client. For practical requests using this source, see the prompt library.

Recommended (with your own key):

{
  "mcpServers": {
    "gsa-perdiem": {
      "command": "uvx",
      "args": ["--refresh-package", "gsa-perdiem-mcp", "--from", "gsa-perdiem-mcp", "gsa-perdiem-mcp"],
      "env": {
        "PERDIEM_API_KEY": "paste-your-api-data-gov-key-here",
        "FEDERAL_API_MIN_INTERVAL_SECONDS": "4"
      }
    }
  }
}

The server defaults FEDERAL_API_MIN_INTERVAL_SECONDS to 4 for personal-key and DEMO_KEY requests. The explicit value above documents the intended policy and can be changed when you have a documented reason. Per Diem and Regulations.gov processes using the same api.data.gov key share the gate.

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

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

The --refresh-package flag tells uv to check PyPI for a newer release each time your client launches the server, so fixes arrive automatically; without it, uv keeps serving whatever version it first cached. It adds a moment of network time at startup, so raise your platform's MCP startup timeout if it enforces a short one.

Restart the client and the tools appear.

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. Non-foreign OCONUS rates (Alaska, Hawaii, territories) are set by DoD (DTMO); foreign rates by 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.

Request pacing

The next request starts after the previous request's duration plus 4 seconds. This is a completion delay, not a 4-second start interval. Local processes sharing the same pacing directory and identity share this gate; a separate local counter does not create additional provider quota.

See the complete pacing reference for all nine servers, shared credentials/IPs, configuration and hosting differences.

Every request, including DEMO_KEY traffic, uses a provisional 4-second cross-process anti-burst interval by default. Per Diem and Regulations.gov share a local api.data.gov bucket when they use the same key. This does not increase provider quota or coordinate the key on another computer. Override with FEDERAL_API_MIN_INTERVAL_SECONDS, use 0 to deliberately disable it, and use FEDERAL_API_PACING_DIR to relocate local pacing state.

License

MIT