What you get and what you write

seampact generates the boundary of your API: the code that checks what comes in and what goes out. You write what happens in between.

What seampact generates

From one YAML contract:

Output	What you get
Types and validators	One type per schema, per request and per reply, with checks on every input. TypeScript with zod, yup, class-validator, VineJS or Ajv on Node. Java records with a generated structural validator on Spring Boot. PHP classes with the Laravel or Symfony validator. Python Pydantic models, or DRF fields. The Node choices are in validators.
Server boundary	Routes for NestJS, Express, Fastify, AdonisJS, Hono, Spring Boot, Laravel, Symfony, FastAPI, Django REST Framework and Django Ninja. They check the input, call your access hooks and check each reply against the contract.
Built-in rules	Paging, rate limits, idempotency keys, ETags, CSRF, signed requests and field rights, declared in the contract and enforced at the boundary. You plug in the stores and decisions.
Errors	One error format, RFC 9457 problem+json by default, with typed error codes per route.
Clients	A typed fetch client, React hooks (TanStack Query, SWR or RTK Query), Vue composables, an Angular service and MSW mock handlers.
Docs	OpenAPI 3.1 documents, and your framework’s own Swagger kept in line with the contract.
Editor support	Schemas that complete and check the contract’s names as you type.

Every guide lists the options of its target: server guides and client guides.

What you write

• The handlers: what each route does, and where your data lives.
• The access decisions: how a credential is checked and how a right is decided. You answer three generated hooks: authenticate, decide and resolve scope. Use the library you already have (Passport, Clerk, Laravel Gates, Spring Security) or your own code. A hook is an object on Node, an interface on Spring Boot, a class on Laravel and Symfony, and a function or class on Python.
• Your app: its config, its secrets and its database. Generated code takes the backend URL and every setting as an argument.

The app refuses to start while an identity, a right, a rule or a scope has no hook, or while a route has no handler.

What seampact does not do

• Business logic, persistence, authentication or authorization decisions.
• A server framework. Generated code uses your framework’s own mechanisms and never replaces them.
• A TypeScript API to write contracts: YAML is the only way. An importer from an OpenAPI document is on the roadmap.
• Right names, roles, a permission model, a wire format or a code style. Where seampact needs a value, it has a default you can rename. Paged lists, envelopes, JSON:API or HAL come from convention packs.
• WebSocket, Server-Sent Events, gRPC or GraphQL.

The commands

The same commands run on every stack. How you type each one is in commands per stack: npx seampact on Node, a Gradle task or the Maven build on the JVM, vendor/bin/seampact on PHP and seampact on Python.

Command	What it does
seampact init	Starts a project: a config and an example contract. Node only.
seampact generate	Writes the code above into the generated folder (outDir).
seampact check	Fails CI when generated files or documents differ from the contract.
seampact diff	Classifies the changes between two versions and tells which are breaking.
seampact lint	Reports contract mistakes before you generate.
seampact explain notes.getNote	Prints one route whole: params, rules, errors, and where each one comes from.
seampact bundle	Packs a contract so other repositories, Node or JVM, pin and reuse it.

Next: the words used in these docs, in the glossary.