API reference

A summary of everything Lyn exposes. Each entry links to the page that explains it.

Exports

import { Lyn, z, logger, LynEnvError, LynDatabaseError } from "@rouret/lyn";
import { pgTable, text, eq, sql /* … */ } from "@rouret/lyn/db";
import { defineConfig } from "@rouret/lyn/config";

Export	Description
Lyn	The application class
z	Zod 4, re-exported
logger	The pino logger used by Lyn · Logging
LynEnvError	Thrown by new Lyn() on invalid environment variables · Environment variables
LynDatabaseError	Thrown by listen() when the database is unreachable · Database
@rouret/lyn/db	Everything from drizzle-orm and drizzle-orm/pg-core · Database
@rouret/lyn/config	defineConfig for an optional lyn.config.ts · Migrations

new Lyn(config?)

Creates an app. Reads and checks the environment variables right away.

Option	Type	Page
env	Record<string, { name: string; type: "string" | "number" | "boolean" }>	Environment variables
cors	{ origin, credentials?, allowedHeaders?, exposedHeaders?, maxAge? }	CORS
rateLimit	{ max, windowMs?, key?, skip? }	Rate limiting
database	{ schema, url?, pool?, logQueries?, migrateOnStart?, statementTimeoutMs? }	Database
start.hideLynLogo	boolean	Server
server.hostname	string, default "127.0.0.1"	Server
server.allowedHosts	string[], default loopback names	Server
server.maxBodyBytes	number, default 1048576	Server
server.requestTimeoutMs	number, default 30000	Server

Routes

app.get(path, handler, validation?)
app.post(path, handler, validation?)
app.put(path, handler, validation?)
app.delete(path, handler, validation?)

Each returns the app, for chaining. validation is { body?, params?, query? }, with no body on get. See Routing and Validation.

Handler context

Field	Description
request	The standard Request
set.status	Response status, defaults to the method's
set.headers	Response Headers
signal	AbortSignal aborted on timeout or client disconnect
body, params, query	Validated inputs, when a schema is given
db	Typed Drizzle instance, when a database is configured

See Handlers.

App members

Member	Description
listen(port?)	Runs the startup checks, then serves on 127.0.0.1 (or server.hostname). Returns a promise of the app. · Server
stop()	Stops the server and closes the database connection. · Server
handle(request)	Runs a Request through the app without a server. Returns a promise of the Response. · Server
url	Base URL of the running server. Throws before listen().
env	Parsed environment variables, typed from config.env.
db	The Drizzle instance. A type error without config.database.

Error codes

INVALID_HOST, VALIDATION, NO_BODY, INVALID_JSON, PAYLOAD_TOO_LARGE, REQUEST_TIMEOUT, TOO_MANY_REQUESTS, UNSUPPORTED_MEDIA_TYPE, NOT_FOUND, METHOD_NOT_ALLOWED, CONFLICT, INTERNAL_SERVER_ERROR. See Errors.

CLI

Command	Description
lyn db generate	Writes the SQL migrations for your schema changes. Needs drizzle-kit.
lyn db migrate	Applies the pending migrations to DATABASE_URL.
lyn db studio	Opens Drizzle Studio on DATABASE_URL. Needs drizzle-kit.

See Migrations.