libraryapi.dev — US Public Library API

# libraryapi.dev — LLM Reference libraryapi.dev is a REST API for US public library facility, hours, services, and statistics data. Built on the federal IMLS Public Libraries Survey (PLS) — an annual census of every public library system and outlet in the United States. Public domain data, commercially usable. Base URL: https://api.libraryapi.dev Current version: v1 Data vintage: IMLS PLS FY 2023 (released August 2025) Coverage: 9,252 library systems + 17,586 outlets across the 50 states, DC, and outlying territories (PR, GU, MP, AS, VI). Response rate: 96-97%. --- ## Authentication Pass an API key on every request using one of: Header: X-API-Key: sk_live_... Header: Authorization: Bearer sk_live_... API keys are obtained free at https://libraryapi.dev/pricing (500 requests/month, no credit card). GET /v1/health does NOT require an API key. --- ## Rate Limits | Plan | Per minute | Per month | |------------|------------|-----------| | Free | 10 | 500 | | Starter | 60 | 10,000 | | Pro | 120 | 50,000 | | Growth | 300 | 200,000 | Exceeding per-minute limit → 429 RATE_LIMITED Exceeding monthly limit → 402 QUOTA_EXCEEDED Monthly quotas reset on the 1st of each calendar month. --- ## Response Envelope Every successful response uses this envelope: { "data": <object or array — see each endpoint>, "meta": { "requestId": "req_d00aa00a7fee", "creditsUsed": 1, "creditsRemaining": 499 }, "source": { "imlsYear": "FY 2023", "updatedAt": "2025-08-15", "freshnessDays": 273 } } All field names in responses are camelCase. Each API call costs 1 credit regardless of results returned. --- ## Key Concepts **Library system** (also "administrative entity" or "AE" in IMLS docs): The administrative unit — typically a county, city, or multi-jurisdictional library system that operates one or more outlets. Identified by FSCSKEY (a 6-character ID like "CA0109")