API is interface allowing different software to communicate. Enables integrations—your product talks to other products. Example: Stripe API lets apps process payments. RESTful APIs most common. Critical for SaaS products.
API explained: Software communicates via structured requests/responses. Example: Your app sends "process payment for ₹999" to Stripe API, Stripe returns "payment successful, ID 12345." No need to build payment processing—use API. API types: REST API (most common—uses HTTP, returns JSON), GraphQL (query exactly what you need), SOAP (old, enterprise), Webhooks (push notifications when events happen). API use cases for startups: (1) Integrate with other products—Payment processing (Stripe, Razorpay), Email (SendGrid, Mailchimp), SMS (Twilio), Cloud storage (AWS S3, Google Cloud), Maps (Google Maps), Authentication (Auth0, Firebase). (2) Build integrations INTO your product—Zapier integrations (connect to 5,000+ apps), Slack bot (post updates to Slack), CRM sync (sync data to Salesforce), Analytics (send events to Mixpanel). (3) Offer your product as API—Developer tool companies (Stripe, Twilio, Plaid) ARE their API, SaaS with API enables enterprise deals (customers want programmatic access). API-first strategy: Build API before UI (enables multiple interfaces—web, mobile, voice), Offer free tier to developers (Stripe approach), Document extensively (clear docs = more adoption), Provide SDKs (Python, Node.js, Ruby libraries). API business models: Usage-based (Stripe charges per transaction, Twilio charges per SMS), Freemium (free for <1K calls/month, paid after), Enterprise (unlimited API access at fixed price).
API Call = Request (URL, Method, Headers, Body) + Response (Status Code, Data). RESTful: GET (retrieve), POST (create), PUT (update), DELETE (remove)API-first company. Developers integrate in 7 lines of code. API so good developers choose Stripe over competitors. $95B company built on API simplicity.
Programmable SMS/voice. API enables: "Send SMS to +1234567890 with message X." Used by Uber, Airbnb, WhatsApp for notifications. $50B+ at peak.
SaaS built UI-first, added API as afterthought. Poor documentation, breaking changes. Enterprise customers left for competitors with stable APIs. Lost ₹5 crore+ ARR.
APIs enable integrations—key for SaaS growth. Products with Zapier integration get discovered by 5M+ users. Offering API enables enterprise deals (they want programmatic access). API-first companies scale faster—Stripe, Twilio, Plaid, Algolia all API-first. Good API = product itself (Stripe's API IS Stripe).
If B2B SaaS: Build API from day 1 (enterprise customers expect it). If B2C: Add API after PMF when integrations needed. Developer tool companies: API IS the product.
Usage-based (per API call—Stripe model), Tiered (free up to N calls, paid after—Twilio model), Enterprise (unlimited at fixed price), Freemium (free tier for developers, paid for production).
Clear documentation (examples for every endpoint), Consistent naming (RESTful conventions), Fast response times (<100ms), Versioning (no breaking changes), Good error messages (specific, actionable).
StartupIdeasDB has 3,000+ validated problems to help you build the next big thing.
Browse Problems →