Dev Mode V2 for AWS Lambda

Serverless Dev Mode runs real invocations of your deployed AWS Lambda functions on your machine, against your actual cloud environment. V2 rebuilds that loop: starting Dev Mode is much faster - ~30 functions are initialized in Dev Mode within 20 seconds - stopping it restores everything automatically, and it is built from the ground up for the way developers and AI coding agents work now.

That makes it the best Lambda development experience available. No stub deploy, no redeploy, Node.js, TypeScript and Python, and an agent works the exact loop you use: start a session, invoke your code, read the results. No other tool combines all of it, and it closes the gap emulation tools leave open - what you test locally is not what runs.

Dev Mode guide - how it works, permissions, limits and troubleshooting
serverless dev reference - every command, option and JSON result
Example - a TypeScript API and a Python queue worker, with a walkthrough for a person and for an agent
Release notes - everything else in v4.44.0

What's new in Dev Mode V2

Dev Mode V2 ships with Serverless Framework v4.44.0. Here is everything that changed in Dev Mode:

Ctrl+C restores everything. The old Dev Mode left your stage answering "Dev Mode Disconnected" until you redeployed. In V2, Ctrl+C restores every function, with nothing to redeploy, and ~30 functions are initialized in Dev Mode within 20 seconds.
No CloudFormation in the loop. Dev Mode V2 bypasses CloudFormation for the dev workflow, so attaching and restoring functions while iterating is MUCH faster. The slowest part of traditional serverless development is simply gone.
Instant reloads. Save a file and the next invocation runs your new code, with no redeploy. Relaying each invocation between AWS and your machine adds only about 0.4-0.8 seconds.
Safe by default. If a session is killed, the next serverless dev, serverless deploy or serverless remove (or serverless dev restore) restores your functions, and in the meantime they keep running the deployed code. Dev Mode refuses the prod and production stages.
A serious speedup for AI agent looping. Agents develop and test by looping: edit, invoke, read the result, edit again. Every element of V2 - instant reloads, agent commands, structured output, the dev-mode skill - compounds inside that loop, so agents converge on working code in a fraction of the sessions and iterations. For agent-driven development, this is a step change, not an increment.
No more 25-function cap. A bug in the old Dev Mode limited a session to 25 functions. In V2, one session covers every function, whatever the size of the service.
Choose the functions you hold. Pick which functions your session holds when you start it, with serverless dev --function <name> or serverless dev --skip-function <name>. While you hold a function, every invocation of it runs on your laptop, so each developer (or agent) works on their own stage.
--detach and agent commands. Run Dev Mode in the background, then use serverless dev status, wait, requests and replay from anywhere. Your session keeps working while you (or your agent) issue commands on demand.
The serverless-dev-mode Agent Skill. A bundled skill teaches any AI coding agent how to drive Dev Mode out of the box - how to attach, invoke, stream invocations, and read request logs. Point your agent at it and it's productive in minutes.
Agent-first CLI output. The CLI now adapts its output for AI coding agents, and NO_COLOR/FORCE_COLOR work across every command, so machine-readable feedback is consistent everywhere.
Node.js, TypeScript and Python. Dev Mode runs Node.js, TypeScript and Python functions, with the same real-invocation fidelity.

How it works

Run serverless dev on your own stage - one stage per developer or agent. Dev Mode attaches your deployed functions in place and relays their real invocations to your machine, where your local code runs them and streams the results back. While you hold a function, every invocation of it runs on your laptop, with real AWS context.

serverless dev --stage <your-name>

serverless dev --stage <your-name> --detach
serverless dev status
serverless dev wait --for invocation --json

Each function can be held by only one session at a time, and Dev Mode shows you when someone else is attached and why. Press Ctrl+C and every function goes back to its deployed code, with nothing to redeploy.

Getting started

Serverless Framework v4 updates itself, so unpinned projects already run v4.44.0. If you pin frameworkVersion, raise it to 4.44.0.

Then run serverless dev --stage <your-name> in any Serverless Framework service, or let your coding agent take it from here with the serverless-dev-mode skill.

Onboarding your coding agent is one command. In your service directory, run:

serverless agent skills install

That installs the bundled skills - including serverless-dev-mode - into the agent directories your team already uses, such as .claude/skills/ or .agents/skills/ (or force a target with --dir). The command is idempotent and refreshing it is the same command, so every agent on the team stays current with each CLI release. From there your agent attaches to Dev Mode, starts a session in the background, waits for real invocations, reads what each one received and returned, and replays them - driving the whole develop-and-test loop on its own.

Learn more:

Dev Mode guide - how it works, permissions, limits and troubleshooting
serverless dev reference - every command, option and JSON result
Example - a TypeScript API and a Python queue worker, with a walkthrough for a person and for an agent
Release notes - everything else in v4.44.0

If you build on AWS Lambda, this is the loop you've been waiting for.

Also in v4.44.0

Sandbox hardening. The serverless dev --sandbox emulator (Lambda MicroVMs) now blocks cross-site and DNS-rebinding requests, so your local dev session is safe inside your network.
Stability fixes. Node.js 26 deploys no longer hang, config validation no longer fails with the formats0 error, and concurrent first deploys into a new region no longer race on the shared deployment bucket.

What's new in Dev Mode V2

Dev Mode V2 ships with Serverless Framework v4.44.0. Here is everything that changed in Dev Mode:

Ctrl+C restores everything. The old Dev Mode left your stage answering "Dev Mode Disconnected" until you redeployed. In V2, Ctrl+C restores every function, with nothing to redeploy, and ~30 functions are initialized in Dev Mode within 20 seconds.

No CloudFormation in the loop. Dev Mode V2 bypasses CloudFormation for the dev workflow, so attaching and restoring functions while iterating is MUCH faster. The slowest part of traditional serverless development is simply gone.

Instant reloads. Save a file and the next invocation runs your new code, with no redeploy. Relaying each invocation between AWS and your machine adds only about 0.4-0.8 seconds.

Safe by default. If a session is killed, the next serverless dev, serverless deploy or serverless remove (or serverless dev restore) restores your functions, and in the meantime they keep running the deployed code. Dev Mode refuses the prod and production stages.

A serious speedup for AI agent looping. Agents develop and test by looping: edit, invoke, read the result, edit again. Every element of V2 - instant reloads, agent commands, structured output, the dev-mode skill - compounds inside that loop, so agents converge on working code in a fraction of the sessions and iterations. For agent-driven development, this is a step change, not an increment.

No more 25-function cap. A bug in the old Dev Mode limited a session to 25 functions. In V2, one session covers every function, whatever the size of the service.

Choose the functions you hold. Pick which functions your session holds when you start it, with serverless dev --function <name> or serverless dev --skip-function <name>. While you hold a function, every invocation of it runs on your laptop, so each developer (or agent) works on their own stage.

--detach and agent commands. Run Dev Mode in the background, then use serverless dev status, wait, requests and replay from anywhere. Your session keeps working while you (or your agent) issue commands on demand.

The serverless-dev-mode Agent Skill. A bundled skill teaches any AI coding agent how to drive Dev Mode out of the box - how to attach, invoke, stream invocations, and read request logs. Point your agent at it and it's productive in minutes.

Agent-first CLI output. The CLI now adapts its output for AI coding agents, and NO_COLOR/FORCE_COLOR work across every command, so machine-readable feedback is consistent everywhere.

Node.js, TypeScript and Python. Dev Mode runs Node.js, TypeScript and Python functions, with the same real-invocation fidelity.

How it works

serverless dev --stage <your-name>

serverless dev --stage <your-name> --detach
serverless dev status
serverless dev wait --for invocation --json

Getting started

Serverless Framework v4 updates itself, so unpinned projects already run v4.44.0. If you pin frameworkVersion, raise it to 4.44.0.

Then run serverless dev --stage <your-name> in any Serverless Framework service, or let your coding agent take it from here with the serverless-dev-mode skill.

Onboarding your coding agent is one command. In your service directory, run:

serverless agent skills install

Learn more:

Dev Mode guide - how it works, permissions, limits and troubleshooting

serverless dev reference - every command, option and JSON result

Example - a TypeScript API and a Python queue worker, with a walkthrough for a person and for an agent

Release notes - everything else in v4.44.0

If you build on AWS Lambda, this is the loop you've been waiting for.

Also in v4.44.0

Sandbox hardening. The serverless dev --sandbox emulator (Lambda MicroVMs) now blocks cross-site and DNS-rebinding requests, so your local dev session is safe inside your network.

Stability fixes. Node.js 26 deploys no longer hang, config validation no longer fails with the formats0 error, and concurrent first deploys into a new region no longer race on the shared deployment bucket.