Free Government & Science APIs — ranked by value

Public, scientific & space data

Scores rate free-tier value on a 1–10 scale. How scores work →

NASA Open APIs Government & Science API key Unified portal for NASA datasets including Astronomy Picture of the Day, Mars rover photos, near-Earth objects, and Earth imagery. 30 req/hr
USGS Water Data APIs Government & Science No auth Machine-readable REST access to US streamflow, groundwater, and water-quality monitoring data. Fair use
openFDA Government & Science API key FDA data on drugs, devices, foods, and adverse-event reports exposed as a public REST API. 240 req/min
US Census Bureau API Government & Science API key Programmatic access to US demographic, economic, and geographic survey datasets. 500 req/day
Open Notify (ISS) Government & Science No auth Simple API reporting the International Space Station's current location and people in space. No published cap
SpaceX API (r/SpaceX) Government & Science No auth Community REST API covering SpaceX launches, rockets, capsules, cores, and crew data. 50 req/sec
arXiv API Government & Science No auth Search and retrieve metadata for millions of open-access scientific preprints across physics, math, and CS. 1 req
Semantic Scholar API Government & Science API key AI-powered scholarly graph API for paper metadata, citations, authors, and embeddings. 1k req/sec
Crossref REST API Government & Science No auth Lookup DOI metadata, references, and funding for over 150 million scholarly works. 50 req/sec
PubMed E-utilities Government & Science API key NCBI's E-utilities for searching and fetching biomedical literature and life-science databases. 3 req/sec
disease.sh COVID-19 API Government & Science No auth Open API aggregating COVID-19, influenza, and vaccine statistics from authoritative global sources. 200 req/min
GBIF API Government & Science No auth Global Biodiversity Information Facility API for species occurrence records and taxonomy worldwide. Fair use
iNaturalist API Government & Science OAuth Access crowdsourced species observations, photos, and identifications from the iNaturalist community. 60 req/min
eBird API 2.0 Government & Science API key Cornell Lab's API for bird sighting records, hotspots, and regional checklists from eBird. Fair use
Europe PMC API Government & Science No auth Search and retrieve life-science literature, abstracts, full text, and citations from Europe PMC. 10 req/sec
ORCID Public API Government & Science OAuth Resolve researcher identifiers and their public works, affiliations, and biographical records. 24 req/sec
DataCite REST API Government & Science No auth Query and resolve DOIs and metadata for research datasets, software, and other outputs. Fair use
PubChem PUG REST Government & Science No auth Retrieve chemical compound structures, properties, and bioactivity data from NIH's PubChem. 5 req/sec
USAspending API Government & Science No auth Comprehensive open data on US federal spending, awards, contracts, and agency budgets. Fair use
OpenFEC API Government & Science API key Federal Election Commission API for US campaign finance filings, contributions, and committee data. 30/hr
AirNow API Government & Science API key EPA air quality index observations and forecasts for US locations by zip code or coordinates. 500 req/hr
Launch Library 2 (The Space Devs) Government & Science No auth Aggregated API of upcoming and past rocket launches, events, agencies, and spacecraft worldwide. 15 req/hr
Sunrise-Sunset API Government & Science No auth Compute sunrise, sunset, and twilight times for any latitude and longitude on a given date. No published cap
CORE API Government & Science API key Search and retrieve metadata and full text from the world's largest aggregation of open-access papers. 10k tok/day
ChEMBL API Government & Science No auth EMBL-EBI bioactivity database API for drug-like molecules, targets, and assay data. Fair use
Open Disease / WHO COVID Tracking Government & Science No auth Historical and current COVID-19 case, recovery, and death counts aggregated by country. Deprecated
NASA Open Science Data Repository Government & Science No auth RESTful API for NASA's space biology and bioinformatics datasets, metadata, and study files. Fair use