API-First Development
Term 12 of 68 in the ERPStack technical glossary
What is API-First Development?
API-First Development is an engineering approach that prioritizes the design and implementation of application programming interfaces (APIs) before building frontend client applications, ensuring system modules can easily integrate with external systems.
API-First Development at a glance
- Order of work
- The contract is designed and agreed before either side writes 1 line of implementation
- Artefacts
- 1 machine-readable schema plus generated types, so client and server cannot drift
- Reference stack
- TypeScript 5.9 types with Zod 4 runtime validation at the boundary
- Versioning rule
- Additive changes are free; removals need 2 supported versions and a deprecation window
- Built with
- TypeScript 5.9 types generated from 1 schema, Zod 4 at the boundary, served by Next.js 16 over REST, GraphQL or tRPC, contract checks run by Vitest 4 and Playwright 1.59 in GitHub Actions
- Numbers that matter
- 1 contract agreed before code; 2 versions live during a migration; 0 hand-written client types; 3 things to fix, naming, errors, pagination
- Contract styles
- REST, a GraphQL API Schema, or tRPC Protocol procedures for internal clients
- Toolchain
- TypeScript, Zod, Vitest, Playwright and GitHub Actions enforcing the contract
- Who consumes the contract
- A Next.js 16 and React 19 web client, mobile, partner systems over REST or a GraphQL API Schema, and internal callers on tRPC Protocol — 4 audiences, 1 schema, 0 duplicated types.
How API-First Development works in production
The ERPStack approach to API-First Development
We build all ERP systems with an API-first approach, using tRPC and Zod schemas. This ensures that your backend forms a single source of truth that any mobile app or procurement channel can securely query.
Frequently asked questions about API-First Development
What does API-First Development change in practice?
It moves the hardest conversation to the start. In API-First Development the contract — resources, fields, errors, pagination — is agreed before implementation, so frontend and backend can build in parallel against the same definition. The alternative is an API that accretes from whatever the first screen happened to need, which produces inconsistent naming, unpredictable error handling and a surface no second client can use.
Doesn't designing the contract first slow the project down?
It front-loads a cost that is otherwise paid with interest. API-First Development spends days on a contract to avoid weeks of rework when a second consumer arrives and the existing surface cannot serve it. Because the contract unblocks parallel work immediately, calendar time is often shorter even when the design step is counted honestly.
How do you stop client and server drifting apart?
Generate, do not document. API-First Development works when types come from 1 machine-readable schema and both sides import them, so an incompatible change fails at compile time rather than in production. ERPStack pairs TypeScript 5.9 types with Zod 4 validation at the runtime boundary, because types alone do not protect you from a payload that lies about its shape.
How should an API be versioned?
By preferring additive change. Under API-First Development you add fields and new endpoints freely, since existing clients ignore what they do not read. Removing or renaming is the expensive operation: it needs a new version, 2 supported surfaces during the overlap, and a deprecation window long enough for consumers you do not control. Designing so removals are rare is worth more than any versioning scheme.