`@fastify/env`

Loads and validates environment variables against a JSON Schema.

Since Fastify 5 Spec ↗

Syntax

app.register(fastifyEnv, { schema, dotenv? })

Parameters

Name	Type	Required	Description
`options`	`object`	No	schema for required env vars, plus dotenv and confKey options.

Returns

Promise<void> — Resolves after validation, rejecting on failure.

Throws

Error — Rejected at boot when a required variable is missing or invalid.

Examples

import Fastify from 'fastify';
import fastifyEnv from '@fastify/env';

const app = Fastify();

await app.register(fastifyEnv, {
  dotenv: true,
  schema: {
    type: 'object',
    required: ['PORT', 'DATABASE_URL'],
    properties: {
      PORT: { type: 'number', default: 3000 },
      DATABASE_URL: { type: 'string' },
    },
  },
});

app.get('/cfg', async () => ({ port: app.config.PORT }));

Notes

Validated values are exposed on app.config (configurable via confKey). The app fails fast at boot if required variables are missing, surfacing misconfiguration early.