Feature

API Key Authentication

Simple key-based authentication for server-to-server calls.

81 providers 1343 APIs 76 declared variants

Authentication via an issued API key or secret passed in a header or query parameter. The lowest-friction path to a first successful call, and still the default for most machine-to-machine integrations.

81 API providers on the APIs.io network offer api key authentication. The highest-rated are Ashby, OpenAI, PropelAuth, Factorial, Truework.

Providers

Ranked by API Evangelist rating — Exemplar and Strong are expanded by default.

Exemplar 9 Complete, well-documented, and agent-ready
Ashby Ashby is a modern all-in-one recruiting platform combining Applicant Tracking System (ATS), sourcing/CRM, i... 52 APIs 75.3 OpenAI APIs for accessing OpenAI's artificial intelligence models including GPT, DALL-E, Whisper, and Embeddings. 51 APIs 69.0 PropelAuth PropelAuth is a B2B SaaS authentication and multi-tenant user management platform purpose-built for organiz... 18 APIs 68.7 Factorial Factorial is an all-in-one HR, payroll, time, talent, finance, and IT management platform headquartered in ... 22 APIs 68.6 Truework Truework operates a unified income and employment verification platform for mortgage lenders, credit unions... 5 APIs 68.2 Amplitude Amplitude is a digital analytics platform that helps product teams understand user behavior, run experiment... 33 APIs 68.0 Adafruit IO Adafruit IO is a cloud Internet of Things platform from Adafruit Industries built for makers, hobbyists, st... 12 APIs 67.6 sensible-so Sensible is a document-automation API platform that extracts structured data from PDFs, images, spreadsheet... 7 APIs 67.1 Amazon Managed Grafana Amazon Managed Grafana is a fully managed service for open source Grafana developed in collaboration with G... 3 APIs 66.2
Strong 33 Solid coverage with minor gaps
PolyAPI Poly, built using cutting-edge AI and Kubernetes-native technology, accelerates development and simplifies ... 10 APIs 65.2 ThingSpeak ThingSpeak is an IoT analytics platform from MathWorks that lets devices aggregate, visualize, and analyze ... 12 APIs 64.7 Viam Viam is a robotics and edge AI platform founded in 2020 by Eliot Horowitz (MongoDB co-founder and former CT... 52 APIs 64.7 Leonardo.AI Leonardo.AI is an Australian generative-AI company (acquired by Canva in July 2024) offering a Production A... 14 APIs 64.0 PostHog PostHog is an open source product analytics platform that provides event tracking, session recording, featu... 139 APIs 63.7 OpsGenie OpsGenie is an incident management and alerting platform, now part of Atlassian, that helps operations team... 15 APIs 63.0 Paperspace Paperspace is a GPU cloud platform for AI, ML, and 3D rendering workloads, acquired by DigitalOcean in 2023... 25 APIs 62.3 Greenhouse Greenhouse Software is an enterprise applicant tracking system (ATS) and end-to-end hiring platform spannin... 27 APIs 62.1 IonQ IonQ (NYSE IONQ) is a College Park, Maryland-based public trapped-ion quantum computing company. IonQ desig... 7 APIs 62.1 Adapt Adapt (adapt.io) is a B2B lead intelligence and sales acceleration platform that provides a database of 250... 4 APIs 61.9 Lambda Lambda gives your team instant access to the compute you need to build and deploy Artificial Intelligence. ... 5 APIs 61.7 Inworld AI Inworld AI is a real-time voice AI infrastructure provider. The Inworld platform delivers text-to-speech, s... 7 APIs 61.6 FastDOL Federal workplace enforcement records on 2.3M US employers across 16 federal agencies — OSHA, WHD, MSHA, EP... 11 APIs 61.5 Calendarific Worldwide public holidays REST API covering 230+ countries. Calendarific provides national, local, religiou... 3 APIs 61.4 Albato A Single No Code Platform For All Automations Albato is a no-code automation platform enabling businesses to automate workflows by integrating 1,000+ app... 5 APIs 61.1 Mindee Mindee is a document parsing and intelligent document processing platform. Its REST API (api-v2.mindee.net)... 6 APIs 60.6 StackOne StackOne is an AI-powered embedded integration platform as a service (iPaaS) designed to simplify and accel... 33 APIs 60.4 Vonage Vonage (part of Ericsson) provides cloud communications APIs for voice, SMS, messaging, video, and verifica... 9 APIs 60.1 Bandwidth Bandwidth is a leading cloud-based communications platform providing voice, messaging, emergency calling, p... 18 APIs 59.8 UserGems UserGems is a San Francisco-based sales intelligence platform that tracks champion job changes and surfaces... 3 APIs 59.7 VesselFinder VesselFinder is a maritime intelligence company operating a global AIS vessel-tracking network (terrestrial... 10 APIs 59.5 Continue Continue is the open-source AI code assistant for VS Code and JetBrains, distributed under Apache 2.0. The ... 5 APIs 58.9 ShipStation ShipStation is a leading shipping platform for ecommerce businesses providing APIs to integrate shipping wo... 11 APIs 58.9 Track-POD Track-POD is a cloud-based delivery management platform that combines route planning and optimization with ... 8 APIs 58.6 arcade-dev Arcade.dev (formerly Arcade AI) is the MCP runtime for production AI agents — a platform that lets agents s... 8 APIs 58.5 Smithery Smithery is an MCP server registry and hosting platform that lets developers discover, publish, and connect... 9 APIs 58.3 API Snap API Snap is a developer utility platform that consolidates 13+ commonly needed REST APIs into a single, uni... 5 APIs 57.7 Sorsa Sorsa Labs operates a real-time X (Twitter) data API providing developers access to tweets, profiles, searc... 8 APIs 57.7 Unkey Unkey is the developer platform for modern APIs, providing globally distributed API key management, rate li... 8 APIs 57.6 EPA — U.S. Environmental Protection Agency Web services, data products, and open data spanning the U.S. Environmental Protection Agency. Programmatic ... 137 APIs 57.3 Iterable Iterable is an AI customer engagement platform that powers unified cross-channel marketing experiences and ... 23 APIs 57.2 Typesense Typesense is a fast, typo-tolerant, open-source search engine designed for developer productivity. It provi... 25 APIs 56.7 Australia Post Australia Post is Australia's primary postal operator, offering a developer platform with REST APIs for e-c... 4 APIs 56.1
Developing 25 Usable, with meaningful gaps to close
Robin AI Robin AI is a London-headquartered legal intelligence platform founded in 2019 by former Clifford Chance di... 5 APIs 55.8 Magic Eden Magic Eden is a multi-chain NFT marketplace and trading platform supporting Solana, Bitcoin (Ordinals and R... 11 APIs 55.1 Ubiquiti Ubiquiti Inc. (NYSE: UI) is an American networking technology company that designs and sells wireless a... 8 APIs 54.3 Kushki Kushki is an Ecuador-headquartered LatAm fintech operating as a regional non-banking acquirer for the Andea... 12 APIs 54.2 Magic Eden Magic Eden is a multi-chain NFT marketplace offering REST and instruction-generation APIs for Solana, EVM c... 19 APIs 54.2 Abstract API Abstract API is a platform that offers a wide range of API services for developers to easily integrate vari... 14 APIs 54.0 TomTom TomTom provides a comprehensive suite of location technology APIs and SDKs including maps, search, routing,... 20 APIs 53.5 Lever Lever is a talent acquisition and applicant tracking platform built on the Opportunities data model. The Le... 41 APIs 53.4 Apollo.io Apollo.io is a sales intelligence and engagement platform combining a 270M+ contact database with email and... 35 APIs 53.3 Elastic Elastic is a software company that builds search-powered solutions for observability, security, and search ... 12 APIs 52.4 TrackingMore TrackingMore is a multi-carrier shipment tracking platform offering a unified REST API that integrates with... 3 APIs 52.2 Tensor Tensor is the Solana-native NFT marketplace and trading protocol founded by Tensor HQ and now stewarded by ... 9 APIs 52.0 Aligned News Aligned News is an AI-native intelligence and news platform that synthesizes AI-powered briefings from 63 c... 8 APIs 51.8 Epidemic Sound Epidemic Sound is a Stockholm-based royalty-free music and sound effects licensing platform for video creat... 9 APIs 49.7 openFDA openFDA is the U.S. Food and Drug Administration's public data platform, providing Elasticsearch-backed RES... 6 APIs 49.6 honeycomb Build integrations and automate workflows with the Honeycomb API. Programmatically manage datasets, queries... 22 APIs 49.0 trello Trello is a web-based, kanban-style, list-making application that allows users to organize tasks, projects,... 16 APIs 47.4 Loops Loops is a modern email platform purpose-built for software companies, combining product, marketing, and tr... 12 APIs 46.6 Agricultural Statistics Service The National Agricultural Statistics Service (NASS) is an agency of the United States Department of Agricul... 5 APIs 45.9 US Census Bureau The U.S. Census Bureau is the federal statistical agency responsible for producing data about the American ... 19 APIs 44.7 Redis Redis is an open source, in-memory data structure store used as a database, cache, message broker, and stre... 4 APIs 44.4 Chicago Transit Authority The Chicago Transit Authority (CTA) is the public transit operator for the City of Chicago and 35 surroundi... 11 APIs 43.9 RocketReach RocketReach is a Seattle-based B2B contact data and sales intelligence provider that maintains a database o... 3 APIs 43.4 NOAA — National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (NOAA) is the United States scientific and regulatory a... 24 APIs 43.1 NASA Open APIs NASA Open APIs is the National Aeronautics and Space Administration's unified, public developer portal expo... 34 APIs 42.5
Thin 9 Limited public surface area
Lemon Squeezy Lemon Squeezy is on a mission to make selling digital products easy-peasy. We know first-hand the challenge... 31 APIs 41.5 celestia Celestia is the first production modular data availability blockchain. It separates consensus and data avai... 10 APIs 41.4 Langflow Langflow is an open-source low-code visual builder for AI agents, RAG pipelines, and LangChain-based workfl... 15 APIs 41.1 Amazon AppSync Amazon AppSync creates serverless GraphQL and Pub/Sub APIs that simplify application development through a ... 9 APIs 39.5 Healthie Healthie is a cloud, API-first EHR and practice management platform purpose-built for digital health startu... 1 API 37.9 Syndica Syndica is a Solana-only infrastructure company building developer infrastructure for Web3. Its production ... 4 APIs 34.5 Greenly Greenly is a Paris-headquartered (with offices in London and New York) carbon accounting platform focused o... 7 APIs 33.2 Paysafe Paysafe is an integrated payment platform providing businesses with REST APIs for online payments, digital ... 9 APIs 30.3 Canada Post Canada Post is the primary postal operator in Canada, offering a developer platform with REST and SOAP web ... 10 APIs 29.0
Emerging 5 Early or largely undocumented
API-Sports API-Sports is a leading provider of real-time sports data and statistics APIs for businesses and developers... 4 APIs 25.6 API Layer APILayer is a curated API marketplace offering 178+ production-ready APIs across categories including finan... 1 API 23.0 Hostfully Hostfully is a San Francisco-based short-term rental (STR) property management platform serving vacation re... 2 APIs 20.3 io.net io.net is a decentralized GPU network for AI compute, built on Solana, that aggregates idle consumer and da... 8 APIs 20.1 API League API League is a comprehensive API marketplace aggregating 60+ best-in-class APIs across categories includin... 1 API 19.7

What Providers Actually Declared

This feature is a canonical term. These are the free-text strings providers wrote in their own apis.yml that map onto it.

10 requests/second per API key with burst to 20 req/s (token bucket)164 REST operations across 14 product modules — Applications, Candidates, Jobs, Openings, Job Postings, Interviews, Offers, Approvals, Surveys, Assessments, Custom Fields, Organization, Files, Reports, Webhooks, API Keys30-day-rotation API keys for programmatic MCP accessAPI Key ApplicationAPI Key AuthenticationAPI Key IssuanceAPI Key Self-ServiceAPI Key TiersAPI KeysAPI Keys Post Expiration WindowAPI Keys: create, verify, list, update, deleteAPI key + secret authAPI key authenticationAPI key authentication via Api-Key header; keys generated and rotated from Account SettingsAPI key authentication via X-Api-Key headerAPI key authentication via `x-api-key` header or query parameterAPI key authentication via the userkey query parameterAPI keys (Bearer)API keys per environmentAPI-key authentication via `Authorization: Basic` + `AuthorizationSource: API` (plus `AuthorizationShard` for sharded customers)Authentication via `x-tensor-api-key` header issued through dev.tensor.trade after Airtable applicationAuthentication: API key via Tracking-Api-Key headerAuto-generated OAuth UI modals for servers requiring API keys or user configurationBasic Access Authorization using Base64-encoded API keyBearer API key authentication; per-second concurrency limits scale by plan (1 → 10 → 25+)Bearer auth with API keys prefixed con_Bearer-token API key authentication with a GET /api-key test endpointBearer-token API keys, prefixed tw_sk_ (production) and tw_sk_test_ (sandbox)Concurrency, queue, and rate-limit controls scoped per API keyEnd-user API keys (personal and org-scoped) with validation, usage stats, and import of legacy keysFree API KeyFree API key with no published rate limit; one key per email; required for all data queriesFree and open weather, climate, ocean, fisheries, and space-weather APIs — no payment required and most endpoints require no API keyFree developer program registration; API keys issued per environment (sandbox and production)Funded by TIA staking and PayForBlobs gas fees; no central API key or commercial pricing tierGenieKey-based authentication (per integration)Granular per-endpoint API key permissions (Harvest API)Header-based authentication (email + apiKey) with 250 requests-per-minute rate limitJWT and API key/secret authJWT-based realtime authentication (separate Realtime-only API keys)

Showing 40 of 76 declared variants