`reply.setCookie()`

Sets a response cookie, available when the cookie plugin is registered.

Since Fastify 5 Spec ↗

Syntax

reply.setCookie(name, value, options?)

Parameters

Name	Type	Required	Description
`name`	`string`	No	The cookie name.
`value`	`string`	No	The cookie value.
`options`	`object`	No	Options like httpOnly, secure, sameSite, path, and signed.

Returns

FastifyReply — The reply, for chaining.

Examples

import Fastify from 'fastify';
import cookie from '@fastify/cookie';

const app = Fastify();
await app.register(cookie, { secret: process.env.COOKIE_SECRET });

app.post('/login', async (_req, reply) => {
  reply.setCookie('sid', 'abc123', {
    httpOnly: true,
    secure: true,
    sameSite: 'lax',
    path: '/',
    signed: true,
  });
  return { ok: true };
});

Notes

Requires @fastify/cookie. Use httpOnly and secure for session cookies and `signed: true` to tamper-protect the value. reply.clearCookie() removes a cookie.