AWS Emulator began as a weekend experiment, when an engineer prompted the Kiro coding agent to build a passable version of Amazon SQS in 15 minutes. (GeekWire File Photo / Todd Bishop)
AWS says its engineers didn’t write or review a single line of code in its newest developer tool, and the company is touting that as a selling point.
AWS Emulator, released Wednesday, simulates AWS services on a developer’s own machine. It’s built from more than 400 API models covering more than 200 AWS services. Developers and AI coding agents can use it to test code without a network connection and without paying for the real cloud.
The tool addresses a problem that coding agents such as Amazon’s Kiro and Anthropic’s Claude Code have made worse. Agents can write code faster than teams can test it against the real cloud. Agents check their work by running the code and reading the results, over and over, and doing that in the cloud adds delays and costs.
The emulator lets them run that loop on a developer’s own machine.
In an ironic or perhaps appropriate twist, AWS used AI agents to build the emulator. Agents also maintain it, testing it against real AWS and fixing the gaps they find.
“The emulator was written entirely by autonomous agents. Our team hasn’t written or reviewed any of the code,” wrote Matt Goldberg, the AWS senior principal engineer behind the project, in a blog post .
Goldberg compared his agents to himself as a kindergartner, too young to hold a crayon properly, who got yelled at by classmates for ruining a group drawing of dinosaurs. The problem wasn’t bad intent, he wrote, just a lack of competence. The answer, for agents, is clearly defined areas to fill in.
“I think agents also need coloring books,” he wrote.
The agents work from AWS’s public API models, which describe how each service should behave, and check their work against the real AWS cloud.
The agents run on Amazon Bedrock AgentCore in three teams. One writes “fidelity tests” — real-world scenarios such as creating a queue, sending a message and deleting the queue — and checks each against real AWS. A second runs those tests against the emulator and files issues for failures, and a third fixes them, one agent per issue.
Every change passes through an automated gate where other agents check coding standards and security. Goldberg wrote that hundreds of agents now fix thousands of issues a day.
The project started as a weekend experiment, inspired by Anthropic’s demonstration earlier this year in which a team of Claude agents built a C compiler . Goldberg gave Kiro a three-step prompt and got a passable first version of Amazon SQS, AWS’s message queuing service, in 15 minutes.
By the end of the weekend, Goldberg wrote, Kiro had built a rough version of the rest of AWS, with obvious gaps, and his team started using it to test its software that Monday.
Swami Sivasubramanian, AWS vice president of agentic AI and emerging tech, tied the project to a lesson he described to GeekWire in June. He spent four nights babysitting Kiro as it tried to rebuild a replication engine he and Allan Vermeulen built by hand nearly 20 years ago.
Once he gave the agent a spec and a way to test its work, the job took about two hours.
“When agents write the code and check their own work, the engineer’s job is to give them room to work on their own and to build the specs, tests, and merge gates that decide when that work is correct,” Sivasubramanian wrote in a guest post on CTO Werner Vogels’ blog.
It’s the same idea behind Amazon’s recent move to rewrite its engineering playbook for an era when AI writes the code.
The emulator has limits. Devin Pratt, an IDC analyst, told InfoWorld that it doesn’t yet simulate throttling, outages or differences in which services and features are available by region, and that it doesn’t sandbox the code it runs. The agents’ backlog of known gaps is public, in a GitHub folder called “things-that-do-not-work.”
Other AWS emulators exist, most notably LocalStack, which this year put its free version behind an account requirement and limited it to noncommercial use. AWS released its emulator for free under CC0, a public domain dedication, with the full commit history on GitHub.
The company says it will share more at its upcoming re:Invent conference.
