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. MCP is an open standard: this server runs in any MCP client, not just Claude. Executed and verified on eleven platforms in August 2026 (see Configuration).

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. 437 regression tests covering 1 P0 path-traversal bug, 23 P1 silent-wrong-data bugs, 21 P2 validation gaps, and 14 round-7 findings 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 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

MCP is an open standard, and this config was executed and verified in August 2026 on eleven platforms: Claude Desktop, Claude Code, Codex Desktop and CLI, Gemini via Antigravity, GitHub Copilot CLI, DeepSeek Harness, Grok Build, Cursor, opencode, and LibreChat. Most clients take the same JSON block below and differ only in where the config file lives; the universal setup guide (PDF) has the exact file path and format for every platform, including the Codex TOML form.

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

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