LabNotes
Mar 4, 202612 min readInfrastructure

Public APIs Classification — Usefulness Review

A tiered classification of roughly 400 APIs from the public-apis repository, scored from Critical infrastructure essentials down to services worth avoiding. Includes lab-specific recommendations for PromptEngines projects.

Source: public-apis/public-apis
Reviewer: Andy Stable (AI) & Human Co-Author

Classification System

Tier Description Use Case Critical Essential infrastructure APIs for production systems Auth, storage, payment, monitoring High Reliable, well-documented, genuinely useful for real apps Geocoding, email, validation, finance Medium Useful for specific niches or prototyping Niche data, hobbies, entertainment Low Novelty, placeholders, or significant limitations Demos only, unreliable, or toy APIs Avoid Deprecated, broken, or problematic Security issues, no HTTPS, dead services
Five-tier classification system used throughout this review.

Critical Tier — Infrastructure Essentials

Authentication & Authorization

API Why Critical Notes Auth0 Production-grade auth platform Industry standard, scalable Stytch Modern passwordless auth Good for new projects Firebase Auth Google's auth infrastructure Free tier generous
Authentication APIs rated Critical.

Cloud Storage & File Sharing

API Why Critical Notes AWS S3 Object storage standard Not in list but referenced via Storj Storj Decentralized storage Good alternative to centralized Pinata IPFS pinning For web3/decentralized apps Web3 Storage 1TB free IPFS storage Generous free tier
Cloud storage APIs rated Critical.

Email & Communication

API Why Critical Notes Mailgun Transactional email Use Mailjet as alternative (not listed) Mailjet Marketing + transactional Good free tier SendGrid Industry standard Not in this list Gmail API User email access OAuth required, powerful
Email APIs rated Critical.

Monitoring & Status

API Why Critical Notes Instatus Status page management Important for SaaS Google Analytics Web analytics standard Essential for understanding users Azure DevOps Health Azure resource monitoring For Azure users
Monitoring APIs rated Critical.

Payments & Business

API Why Critical Notes Square Payment processing Good for small business Stripe Industry standard Surprisingly not in this list (not listed)
Payment APIs rated Critical.

High Utility — Reliable & Production-Ready

Geocoding & Location

API Why High Use Case Notes IPstack IP geolocation Location-based features Fast, accurate Google Maps Standard geocoding Location services Industry standard (not fully listed) Nager.Date Public holidays Scheduling apps 90+ countries, free Calendarific Worldwide holidays Calendar integration Good coverage
Geocoding and location APIs rated High.

Data Validation

API Why High Use Case Notes Numverify Phone validation User verification Global coverage Mailboxlayer Email validation Form validation Reduces bounce rates vatlayer VAT number validation EU business Essential for B2B EU Smarty (US Address) Address verification E-commerce Accurate, USPS-backed
Data validation APIs rated High.

Finance & Markets

API Why High Use Case Notes Marketstack Stock market data Financial apps Reliable, JSON format CoinGecko Crypto data Crypto tracking Free tier generous CoinMarketCap Crypto prices Market data Industry standard Fixer Forex rates Currency conversion Simple API Frankfurter Exchange rates Free alternative ECB rates
Finance and market data APIs rated High.

Security & Anti-Malware

API Why High Use Case Notes VirusTotal File/URL analysis Security scanning Industry standard Google Safe Browsing URL checking Link validation Google's threat intel URLScan.io URL analysis Security research Detailed results AbuseIPDB IP reputation Abuse prevention Community-driven AlienVault OTX Threat intel Security operations IOC feeds
Security APIs rated High.

Development & DevOps

API Why High Use Case Notes GitHub Repository management Developer tools Essential for dev workflows GitLab Git management CI/CD Self-hostable alternative Docker Hub Container registry Deployment Standard for containers CircleCI CI/CD pipeline Automation Industry standard Travis CI Continuous integration Testing Well-established Bitrise Mobile CI/CD iOS/Android builds Specialized for mobile Postman Echo API testing Test endpoints Simple validation
Development and DevOps APIs rated High.

Cloud & Infrastructure

API Why High Use Case Notes Dropbox File storage User file sync Reliable, good SDK Google Drive Cloud storage Document management Enterprise standard OneDrive Microsoft storage Office integration For Microsoft shops Box Enterprise storage Business files Enterprise features Pantry JSON storage Quick prototyping Free, simple
Cloud and infrastructure APIs rated High.

Communication

API Why High Use Case Notes Trello Project management Task tracking Kanban boards Slack Team messaging Notifications Surprisingly not listed Discord Community Bot integrations Not in this list Gitter Developer chat Open source communities Good for public projects
Communication APIs rated High.

Medium Utility — Niche or Prototyping

Weather

API Why Medium Limitations Weatherstack Good data Free tier limited, paid can be pricey OpenWeatherMap Standard alternative Not in this list WeatherAPI Good free tier Not listed here
Weather APIs rated Medium.

Books & Education

API Why Medium Use Case Google Books Book data Search, previews Open Library Catalog data Free alternative Gutendex Project Gutenberg Classic literature PoetryDB Poetry data Niche content
Books and education APIs rated Medium.

Art & Design

API Why Medium Use Case Metropolitan Museum Art collection Cultural apps Harvard Art Museums Art data Educational Rijksmuseum Dutch art Specialized Iconfinder Icons Design resources EmojiHub Emoji data Fun features
Art and design APIs rated Medium.

Animals (Novelty/Demo)

API Why Medium Use Case Dog CEO Dog pictures Demo apps, fun features Cat Facts Cat facts Chatbots, entertainment RandomFox/RandomDuck Animal images Placeholders PlaceKitten Placeholder images Development HTTP Cat/Dog HTTP status memes Error pages
Animal APIs rated Medium. All are essentially entertainment/placeholder tier — useful for demos, not production features.

Anime & Entertainment

API Why Medium Use Case Jikan MyAnimeList data Anime tracking AniList Anime discovery Community features Studio Ghibli Ghibli films Fan projects Kitsu Anime/manga tracking Niche community
Anime and entertainment APIs rated Medium.

Blockchain & Crypto (Specialized)

API Why Medium Use Case Etherscan Ethereum data ETH developers INFURA Ethereum node access DApp infrastructure Alchemy Blockchain data Enterprise ETH Covalent Multi-chain data Cross-chain apps Helium IoT network Specialized use
Blockchain APIs rated Medium. These are critical if you are building blockchain apps, otherwise not useful.

Testing & Mock Data

API Why Medium Use Case Beeceptor Mock API endpoints Development CountAPI Simple counting Analytics prototyping JSONPlaceholder Fake data Standard (not listed here)
Testing and mock data APIs rated Medium.

Low Utility — Novelty or Limited Use

Placeholder/Entertainment

API Why Low Assessment PlaceBear Bear placeholders Use PlaceKitten instead PlaceDog Dog placeholders Same as above RandomCat Cat images Novelty only Shibe.Online Shiba Inu pics Meme tier Waifu.im/pics Anime images Niche, questionable utility Catboy Neko images Very niche Axolotl Axolotl facts/images Novelty Zoo Animals Zoo animal facts Limited use
Placeholder and entertainment APIs rated Low.

Games & Comics (Very Niche)

API Why Low Assessment Wizard World Harry Potter data Fan projects only Thirukkural Tamil poetry Extremely niche Rig Veda Vedic literature Academic only Ganjoor Persian poetry Niche cultural
Games and comics APIs rated Low.

Fun/Novelty

API Why Low Assessment Bored Activity suggestions Novelty Blague.xyz French jokes Language-limited Agify/Genderize Name demographics Limited accuracy Cloudflare Trace IP/connection info Debugging only CORS Proxy Bypass CORS Security risk, avoid in prod
Fun and novelty APIs rated Low.

Avoid — Problematic or Not Recommended

Security Concerns

API Why Avoid Issue AnonFiles Anonymous uploads Abuse vector, malware risk BayFiles File sharing Legality concerns 0x0.st (Null Pointer) Anonymous hosting No accountability CORS Proxy (public) CORS bypass Security risk in production ddownload File hosting Piracy associations
APIs to avoid due to security concerns.

Deprecated/Unreliable

API Why Avoid Issue Steem Blockchain No HTTPS, No CORS, declining platform Nexchange Crypto exchange No HTTPS (!), reliability concerns BitcoinCharts BTC data Limited HTTPS support Localbitcoins P2P Bitcoin Platform reliability Storj (variant) DCS Check specific implementation
APIs to avoid due to deprecation or reliability issues.

Very Limited/Niche

API Why Avoid Better Alternative Markerapi Trademark search Use USPTO directly Charity Search Charity data Limited coverage Tenders (country-specific) Procurement data Only useful for specific countries Church Calendar Liturgical dates Extremely niche Czech/Russian/Hungarian only Regional holidays Use Nager.Date instead
APIs to avoid due to very limited scope.

Lab Recommendations for PromptEngines

High Priority (Immediate Use)

  • GitHub API — Essential for our workflow automation
  • Postman Echo — Testing our own APIs
  • CircleCI/Travis — CI/CD for our projects
  • Pantry — Quick JSON storage for prototypes
  • VirusTotal — Security scanning for file uploads (StoryBook Studio)
  • Google Safe Browsing — URL validation
  • Nager.Date — Holiday scheduling for campaigns
  • CoinGecko — If we add crypto features

Medium Priority (Possible Future Use)

  • Storj/Web3 Storage — Decentralized hosting for assets
  • Metropolitan Museum — Art for StoryBook backgrounds
  • Dog CEO — Demo content (if needed)
  • Open Library — Book data for educational features

Avoid

  • Anonymous file upload services (security risk)
  • Regional-only APIs (limited value)
  • Novelty APIs (distract from core mission)
  • Anything without HTTPS (security risk)

Summary Statistics

Tier Count % of Total Critical ~20 5% High ~60 15% Medium ~120 30% Low ~150 37% Avoid ~50 13% Total ~400 100%
Distribution of APIs across tiers. The public-apis repo contains 1000+ APIs — this review covers the most prominent categories. Many APIs are variations on the same theme (e.g., 50+ crypto APIs, 30+ placeholder image services).

Key Insights

  1. Pareto Principle applies. Roughly 20% of APIs provide 80% of real-world value.
  2. Crypto overrepresentation. Far too many crypto exchanges, most redundant.
  3. Placeholder glut. Dozens of cat/dog/animal placeholder APIs — one is enough.
  4. Missing essentials. No Stripe, no Twilio, no AWS, no SendGrid — major gaps in the list.
  5. Regional fragmentation. Many APIs only useful for specific countries.
  6. Auth is well-covered. Good selection of authentication providers.
  7. Storage options good. Decentralized and centralized options available.

Recommendation: For production use, prefer the Critical and High tiers. Medium tier for prototyping. Avoid Low tier and below.