V5 Migration Guide

This guide is intended to help with migration from Fastify v4 to v5.

Before migrating to v5, please ensure that you have fixed all deprecation warnings from v4. All v4 deprecations have been removed and will no longer work after upgrading.

Long Term Support Cycle

Fastify v5 will only support Node.js v20+. If you are using an older version of Node.js, you will need to upgrade to a newer version to use Fastify v5.

Fastify v4 is still supported until June 30, 2025. If you are unable to upgrade, you should consider buying an end-of-life support plan from HeroDevs.

Why Node.js v20?

Fastify v5 will only support Node.js v20+ because it has significant differences compared to v18, such as better support for node:test. This allows us to provide a better developer experience and streamline maintenance.

Node.js v18 will exit Long Term Support on April 30, 2025, so you should be planning to upgrade to v20 anyway.

Breaking Changes

Full JSON Schema is now required for querystring, params and body and response schemas

Starting with v5, Fastify will require a full JSON schema for the querystring, params and body schema. Note that the jsonShortHand option has been removed as well.

If the default JSON Schema validator is used, you will need to provide a full JSON schema for the querystring, params, body, and response schemas, including the type property.

// v4
fastify.get('/route', {
  schema: {
    querystring: {
      name: { type: 'string' }
    }
  }
}, (req, reply) => {
  reply.send({ hello: req.query.name });
});

// v5
fastify.get('/route', {
  schema: {
    querystring: {
      type: 'object',
      properties: {
        name: { type: 'string' }
      },
      required: ['name']
    }
  }
}, (req, reply) => {
  reply.send({ hello: req.query.name });
});

See #5586 for more details

Note that it's still possible to override the JSON Schema validator to use a different format, such as Zod. This change simplifies that as well.

This change helps with integration of other tools, such as @fastify/swagger.

New logger constructor signature

In Fastify v4, Fastify accepted the options to build a pino logger in the logger option, as well as a custom logger instance. This was the source of significant confusion.

As a result, the logger option will not accept a custom logger anymore in v5. To use a custom logger, you should use the loggerInstance option instead:

// v4
const logger = require('pino')();
const fastify = require('fastify')({
  logger
});

// v5
const loggerInstance = require('pino')();
const fastify = require('fastify')({
  loggerInstance
});

useSemicolonDelimiter false by default

Starting with v5, Fastify instances will no longer default to supporting the use of semicolon delimiters in the query string as they did in v4. This is due to it being non-standard behavior and not adhering to RFC 3986.

If you still wish to use semicolons as delimiters, you can do so by setting useSemicolonDelimiter: true in the server configuration.

const fastify = require('fastify')({
  useSemicolonDelimiter: true
});

The parameters object no longer has a prototype

In v4, the parameters object had a prototype. This is no longer the case in v5. This means that you can no longer access properties inherited from Object on the parameters object, such as toString or hasOwnProperty.

// v4
fastify.get('/route/:name', (req, reply) => {
  console.log(req.params.hasOwnProperty('name')); // true
  return { hello: req.params.name };
});

// v5
fastify.get('/route/:name', (req, reply) => {
  console.log(Object.hasOwn(req.params, 'name')); // true
  return { hello: req.params.name };
});

This increases the security of the application by hardening against prototype pollution attacks.

Type Providers now differentiate between validator and serializer schemas

In v4, the type providers had the same types for both validation and serialization. In v5, the type providers have been split into two separate types: ValidatorSchema and SerializerSchema.

@fastify/type-provider-json-schema-to-ts and @fastify/type-provider-typebox have already been updated: upgrade to the latest version to get the new types. If you are using a custom type provider, you will need to modify it like the following:

--- a/index.ts
+++ b/index.ts
@@ -11,7 +11,8 @@ import {
 import { FromSchema, FromSchemaDefaultOptions, FromSchemaOptions, JSONSchema } from 'json-schema-to-ts'
 
 export interface JsonSchemaToTsProvider<
   Options extends FromSchemaOptions = FromSchemaDefaultOptions
 > extends FastifyTypeProvider {
-  output: this['input'] extends JSONSchema ? FromSchema<this['input'], Options> : unknown;
+  validator: this['schema'] extends JSONSchema ? FromSchema<this['schema'], Options> : unknown;
+  serializer: this['schema'] extends JSONSchema ? FromSchema<this['schema'], Options> : unknown;
 }

Changes to the .listen() method

The variadic argument signature of the .listen() method has been removed. This means that you can no longer call .listen() with a variable number of arguments.

// v4
fastify.listen(8000)

Will become:

// v5
fastify.listen({ port: 8000 })

This was already deprecated in v4 as FSTDEP011, so you should have already updated your code to use the new signature.

Direct return of trailers has been removed

In v4, you could directly return trailers from a handler. This is no longer possible in v5.

// v4
fastify.get('/route', (req, reply) => {
  reply.trailer('ETag', function (reply, payload) {
    return 'custom-etag'
  })
  reply.send('')
});

// v5
fastify.get('/route', (req, reply) => {
  reply.trailer('ETag', async function (reply, payload) {
    return 'custom-etag'
  })
  reply.send('')
});

A callback could also be used. This was already deprecated in v4 as FSTDEP013, so you should have already updated your code to use the new signature.

Streamlined access to route definition

All deprecated properties relating to accessing the route definition have been removed and are now accessed via request.routeOptions.

Code	Description	How to solve	Discussion
FSTDEP012	You are trying to access the deprecated request.context property.	Use request.routeOptions.config or request.routeOptions.schema.	#4216 #5084
FSTDEP015	You are accessing the deprecated request.routeSchema property.	Use request.routeOptions.schema.	#4470
FSTDEP016	You are accessing the deprecated request.routeConfig property.	Use request.routeOptions.config.	#4470
FSTDEP017	You are accessing the deprecated request.routerPath property.	Use request.routeOptions.url.	#4470
FSTDEP018	You are accessing the deprecated request.routerMethod property.	Use request.routeOptions.method.	#4470
FSTDEP019	You are accessing the deprecated reply.context property.	Use reply.routeOptions.config or reply.routeOptions.schema.	#5032 #5084

See #5616 for more information.

reply.redirect() has a new signature

The reply.redirect() method has a new signature: reply.redirect(url: string, code?: number).

// v4
reply.redirect(301, '/new-route')

Change it to:

// v5
reply.redirect('/new-route', 301)

This was already deprecated in v4 as FSTDEP021, so you should have already updated your code to use the new signature.

Modifying reply.sent is now forbidden

In v4, you could modify the reply.sent property to prevent the response from being sent. This is no longer possible in v5, use reply.hijack() instead.

// v4
fastify.get('/route', (req, reply) => {
  reply.sent = true;
  reply.raw.end('hello');
});

Change it to:

// v5
fastify.get('/route', (req, reply) => {
  reply.hijack();
  reply.raw.end('hello');
});

This was already deprecated in v4 as FSTDEP010, so you should have already updated your code to use the new signature.

Constraints for route versioning signature changes

We changed the signature for route versioning constraints. The version and versioning options have been removed and you should use the constraints option instead.

Code	Description	How to solve	Discussion
FSTDEP008	You are using route constraints via the route {version: "..."} option.	Use {constraints: {version: "..."}} option.	#2682
FSTDEP009	You are using a custom route versioning strategy via the server {versioning: "..."} option.	Use {constraints: {version: "..."}} option.	#2682

HEAD routes requires to register before GET when exposeHeadRoutes: true

We have a more strict requirement for custom HEAD route when exposeHeadRoutes: true.

When you provides a custom HEAD route, you must either explicitly set exposeHeadRoutes to false

// v4
fastify.get('/route', {

}, (req, reply) => {
  reply.send({ hello: 'world' });
});

fastify.head('/route', (req, reply) => {
  // ...
});

// v5
fastify.get('/route', {
  exposeHeadRoutes: false
}, (req, reply) => {
  reply.send({ hello: 'world' });
});

fastify.head('/route', (req, reply) => {
  // ...
});

or place the HEAD route before GET.

// v5
fastify.head('/route', (req, reply) => {
  // ...
});

fastify.get('/route', {

}, (req, reply) => {
  reply.send({ hello: 'world' });
});

This was changed in #2700, and the old behavior was deprecated in v4 as FSTDEP007.

Removed request.connection

The request.connection property has been removed in v5. You should use request.socket instead.

// v4
fastify.get('/route', (req, reply) => {
  console.log(req.connection.remoteAddress);
  return { hello: 'world' };
});

// v5
fastify.get('/route', (req, reply) => {
  console.log(req.socket.remoteAddress);
  return { hello: 'world' };
});

This was already deprecated in v4 as FSTDEP05, so you should have already updated your code to use the new signature.

reply.getResponseTime() has been removed, use reply.elapsedTime instead

The reply.getResponseTime() method has been removed in v5. You should use reply.elapsedTime instead.

// v4
fastify.get('/route', (req, reply) => {
  console.log(reply.getResponseTime());
  return { hello: 'world' };
});

// v5
fastify.get('/route', (req, reply) => {
  console.log(reply.elapsedTime);
  return { hello: 'world' };
});

This was already deprecated in v4 as FSTDEP20, so you should have already updated your code to use the new signature.

fastify.hasRoute() now matches the behavior of find-my-way

The fastify.hasRoute() method now matches the behavior of find-my-way and requires the route definition to be passed as it is defined in the route.

// v4
fastify.get('/example/:file(^\\d+).png', function (request, reply) { })

console.log(fastify.hasRoute({
  method: 'GET', 
  url: '/example/12345.png'
)); // true

// v5

fastify.get('/example/:file(^\\d+).png', function (request, reply) { })

console.log(fastify.hasRoute({
  method: 'GET', 
  url: '/example/:file(^\\d+).png'
)); // true

Removal of some non-standard HTTP methods

We have removed the following HTTP methods from Fastify:

• PROPFIND
• PROPPATCH
• MKCOL
• COPY
• MOVE
• LOCK
• UNLOCK
• TRACE
• SEARCH

It's now possible to add them back using the addHttpMethod method.

const fastify = Fastify()

// add a new http method on top of the default ones:
fastify.addHttpMethod('REBIND')

// add a new HTTP method that accepts a body:
fastify.addHttpMethod('REBIND', { hasBody: true })

// reads the HTTP methods list:
fastify.supportedMethods // returns a string array

See #5567 for more information.

Removed support from reference types in decorators

Decorating Request/Reply with a reference type (Array, Object) is now prohibited as this reference is shared amongst all requests.

// v4
fastify.decorateRequest('myObject', { hello: 'world' });

// v5
fastify.decorateRequest('myObject');
fastify.addHook('onRequest', async (req, reply) => {
  req.myObject = { hello: 'world' };
});

or turn it into a function

// v5
fastify.decorateRequest('myObject', () => { hello: 'world' });

or as a getter

// v5
fastify.decorateRequest('myObject', {
  getter () { 
    return { hello: 'world' }
  }
});

See #5462 for more information.

Remove support for DELETE with a Content-Type: application/json header and an empty body

In v4, Fastify allowed DELETE requests with a Content-Type: application/json header and an empty body was accepted. This is no longer allowed in v5.

See #5419 for more information.

Plugins cannot mix callback/promise API anymore

In v4, plugins could mix the callback and promise API, leading to unexpected behavior. This is no longer allowed in v5.

// v4
fastify.register(async function (instance, opts, done) {
  done();
});

// v5
fastify.register(async function (instance, opts) {
  return;
});

or

// v5
fastify.register(function (instance, opts, done) {
  done();
});

Removes getDefaultRoute and setDefaultRoute methods

The getDefaultRoute and setDefaultRoute methods have been removed in v5.

See #4485 and #4480 for more information. This was already deprecated in v4 as FSTDEP014, so you should have already updated your code.

New Features

Diagnostic Channel support

Fastify v5 now supports the Diagnostics Channel API natively and provides a way to trace the lifecycle of a request.

'use strict'

const diagnostics = require('node:diagnostics_channel')
const sget = require('simple-get').concat
const Fastify = require('fastify')

diagnostics.subscribe('tracing:fastify.request.handler:start', (msg) => {
  console.log(msg.route.url) // '/:id'
  console.log(msg.route.method) // 'GET'
})

diagnostics.subscribe('tracing:fastify.request.handler:end', (msg) => {
  // msg is the same as the one emitted by the 'tracing:fastify.request.handler:start' channel
  console.log(msg)
})

diagnostics.subscribe('tracing:fastify.request.handler:error', (msg) => {
  // in case of error
})

const fastify = Fastify()
fastify.route({
  method: 'GET',
  url: '/:id',
  handler: function (req, reply) {
    return { hello: 'world' }
  }
})

fastify.listen({ port: 0 }, function () {
  sget({
    method: 'GET',
    url: fastify.listeningOrigin + '/7'
  }, (err, response, body) => {
    t.error(err)
    t.equal(response.statusCode, 200)
    t.same(JSON.parse(body), { hello: 'world' })
  })
})

See the documentation and #5252 for additional details.

Contributors

The complete list of contributors, across all of the core Fastify packages, is provided below. Please consider contributing to those that are capable of accepting sponsorships.

Contributor	Sponsor Link	Packages
10xLaCroixDrinker	❤️ sponsor	fastify-cli
Bram-dc		fastify; fastify-swagger
BrianValente		fastify
BryanAbate		fastify-cli
Cadienvan	❤️ sponsor	fastify
Cangit		fastify
Cyberlane		fastify-elasticsearch
Eomm	❤️ sponsor	ajv-compiler; fastify; fastify-awilix; fastify-diagnostics-channel; fastify-elasticsearch; fastify-hotwire; fastify-mongodb; fastify-nextjs; fastify-swagger-ui; under-pressure
EstebanDalelR	❤️ sponsor	fastify-cli
Fdawgs	❤️ sponsor	aws-lambda-fastify; csrf-protection; env-schema; fastify; fastify-accepts; fastify-accepts-serializer; fastify-auth; fastify-awilix; fastify-basic-auth; fastify-bearer-auth; fastify-caching; fastify-circuit-breaker; fastify-cli; fastify-cookie; fastify-cors; fastify-diagnostics-channel; fastify-elasticsearch; fastify-env; fastify-error; fastify-etag; fastify-express; fastify-flash; fastify-formbody; fastify-funky; fastify-helmet; fastify-hotwire; fastify-http-proxy; fastify-jwt; fastify-kafka; fastify-leveldb; fastify-mongodb; fastify-multipart; fastify-mysql; fastify-nextjs; fastify-oauth2; fastify-passport; fastify-plugin; fastify-postgres; fastify-rate-limit; fastify-redis; fastify-reply-from; fastify-request-context; fastify-response-validation; fastify-routes; fastify-routes-stats; fastify-schedule; fastify-secure-session; fastify-sensible; fastify-swagger-ui; fastify-url-data; fastify-websocket; fastify-zipkin; fluent-json-schema; forwarded; middie; point-of-view; process-warning; proxy-addr; safe-regex2; secure-json-parse; under-pressure
Gehbt		fastify-secure-session
Gesma94		fastify-routes-stats
H4ad	❤️ sponsor	aws-lambda-fastify
JohanManders		fastify-secure-session
LiviaMedeiros		fastify
Momy93		fastify-secure-session
MunifTanjim		fastify-swagger-ui
Nanosync		fastify-secure-session
RafaelGSS	❤️ sponsor	fastify; under-pressure
Rantoledo		fastify
SMNBLMRR		fastify
SimoneDevkt		fastify-cli
Tony133		fastify
Uzlopak	❤️ sponsor	fastify; fastify-autoload; fastify-diagnostics-channel; fastify-hotwire; fastify-nextjs; fastify-passport; fastify-plugin; fastify-rate-limit; fastify-routes; fastify-static; fastify-swagger-ui; point-of-view; under-pressure
Zamiell		fastify-secure-session
aadito123		fastify
aaroncadillac	❤️ sponsor	fastify
aarontravass		fastify
acro5piano	❤️ sponsor	fastify-secure-session
adamward459		fastify-cli
adrai	❤️ sponsor	aws-lambda-fastify
alenap93		fastify
alexandrucancescu		fastify-nextjs
anthonyringoet		aws-lambda-fastify
arshcodemod		fastify
autopulated		point-of-view
barbieri		fastify
beyazit		fastify
big-kahuna-burger	❤️ sponsor	fastify-cli; fastify-compress; fastify-helmet
bilalshareef		fastify-routes
blue86321		fastify-swagger-ui
bodinsamuel		fastify-rate-limit
busybox11	❤️ sponsor	fastify
climba03003		csrf-protection; fastify; fastify-accepts; fastify-accepts-serializer; fastify-auth; fastify-basic-auth; fastify-bearer-auth; fastify-caching; fastify-circuit-breaker; fastify-compress; fastify-cors; fastify-env; fastify-etag; fastify-flash; fastify-formbody; fastify-http-proxy; fastify-mongodb; fastify-swagger-ui; fastify-url-data; fastify-websocket; middie
dancastillo	❤️ sponsor	fastify; fastify-basic-auth; fastify-caching; fastify-circuit-breaker; fastify-cors; fastify-helmet; fastify-passport; fastify-response-validation; fastify-routes; fastify-schedule
danny-andrews		fastify-kafka
davidcralph	❤️ sponsor	csrf-protection
davideroffo		under-pressure
dhensby		fastify-cli
dmkng		fastify
domdomegg		fastify
faustman		fastify-cli
floridemai		fluent-json-schema
fox1t		fastify-autoload
giuliowaitforitdavide		fastify
gunters63		fastify-reply-from
gurgunday		fastify; fastify-circuit-breaker; fastify-cookie; fastify-multipart; fastify-mysql; fastify-rate-limit; fastify-response-validation; fastify-sensible; fastify-swagger-ui; fluent-json-schema; middie; proxy-addr; safe-regex2; secure-json-parse
ildella		under-pressure
james-kaguru		fastify
jcbain		fastify-http-proxy
jdhollander		fastify-swagger-ui
jean-michelet		fastify; fastify-autoload; fastify-cli; fastify-mysql; fastify-sensible
johaven		fastify-multipart
jordanebelanger		fastify-plugin
jscheffner		fastify
jsprw		fastify-secure-session
jsumners	❤️ sponsor	ajv-compiler; avvio; csrf-protection; env-schema; fast-json-stringify; fastify; fastify-accepts; fastify-accepts-serializer; fastify-auth; fastify-autoload; fastify-awilix; fastify-basic-auth; fastify-bearer-auth; fastify-caching; fastify-circuit-breaker; fastify-compress; fastify-cookie; fastify-cors; fastify-env; fastify-error; fastify-etag; fastify-express; fastify-flash; fastify-formbody; fastify-funky; fastify-helmet; fastify-http-proxy; fastify-jwt; fastify-kafka; fastify-leveldb; fastify-multipart; fastify-mysql; fastify-oauth2; fastify-plugin; fastify-postgres; fastify-redis; fastify-reply-from; fastify-request-context; fastify-response-validation; fastify-routes; fastify-routes-stats; fastify-schedule; fastify-secure-session; fastify-sensible; fastify-static; fastify-swagger; fastify-swagger-ui; fastify-url-data; fastify-websocket; fastify-zipkin; fluent-json-schema; forwarded; light-my-request; middie; process-warning; proxy-addr; safe-regex2; secure-json-parse; under-pressure
karankraina		under-pressure
kerolloz	❤️ sponsor	fastify-jwt
kibertoad		fastify-rate-limit
kukidon-dev		fastify-passport
kunal097		fastify
lamweili		fastify-sensible
lemonclown		fastify-mongodb
liuhanqu		fastify
matthyk		fastify-plugin
mch-dsk		fastify
mcollina	❤️ sponsor	ajv-compiler; avvio; csrf-protection; fastify; fastify-accepts; fastify-accepts-serializer; fastify-auth; fastify-autoload; fastify-awilix; fastify-basic-auth; fastify-bearer-auth; fastify-caching; fastify-circuit-breaker; fastify-cli; fastify-compress; fastify-cookie; fastify-cors; fastify-diagnostics-channel; fastify-elasticsearch; fastify-env; fastify-etag; fastify-express; fastify-flash; fastify-formbody; fastify-funky; fastify-helmet; fastify-http-proxy; fastify-jwt; fastify-kafka; fastify-leveldb; fastify-multipart; fastify-mysql; fastify-oauth2; fastify-passport; fastify-plugin; fastify-postgres; fastify-rate-limit; fastify-redis; fastify-reply-from; fastify-request-context; fastify-response-validation; fastify-routes; fastify-routes-stats; fastify-schedule; fastify-secure-session; fastify-static; fastify-swagger; fastify-swagger-ui; fastify-url-data; fastify-websocket; fastify-zipkin; fluent-json-schema; light-my-request; middie; point-of-view; proxy-addr; secure-json-parse; under-pressure
melroy89	❤️ sponsor	under-pressure
metcoder95	❤️ sponsor	fastify-elasticsearch
mhamann		fastify-cli
mihaur		fastify-elasticsearch
mikesamm		fastify
mikhael-abdallah		secure-json-parse
miquelfire	❤️ sponsor	fastify-routes
miraries		fastify-swagger-ui
mohab-sameh		fastify
monish001		fastify
moradebianchetti81		fastify
mouhannad-sh		aws-lambda-fastify
multivoltage		point-of-view
muya	❤️ sponsor	under-pressure
mweberxyz		point-of-view
nflaig		fastify
nickfla1		avvio
o-az		process-warning
ojeytonwilliams		csrf-protection
onosendi		fastify-formbody
philippviereck		fastify
pip77		fastify-mongodb
puskin94		fastify
remidewitte		fastify
rozzilla		fastify
samialdury		fastify-cli
sknetl		fastify-cors
sourcecodeit		fastify
synapse		env-schema
timursaurus		secure-json-parse
tlhunter		fastify
tlund101		fastify-rate-limit
ttshivers		fastify-http-proxy
voxpelli	❤️ sponsor	fastify
weixinwu		fastify-cli
zetaraku		fastify-cli