Amazon Web Services released AWS Emulator on Nov. 11, a free tool that imitates more than 200 AWS services on a developer's own machine, and the company says no human wrote or reviewed any of its code. "The emulator was written entirely by autonomous agents. Our team hasn't written or reviewed any of the code," AWS senior principal engineer Matthew Goldberg wrote in a post on Amazon's news site.
The launch gives coding agents a local copy of AWS to test against and doubles as a public case study in agents shipping software without human review. The source is on GitHub under a CC0 public domain dedication with its full commit history, according to GeekWire.
What the tool does
According to the AWS News Blog, the emulator is built from more than 400 API models, the same ones the AWS SDKs use, so requests and errors come back in the same shape as on AWS. Developer tools and coding agents talk to it over a local HTTPS endpoint. It is written in Rust and carries no service fee.
GeekWire reported that the tool targets a problem that coding agents such as Amazon's Kiro and Anthropic's Claude Code have made worse. Agents write code faster than teams can test it against the real cloud, and running that check loop in the cloud adds delays and cost.
AWS listed limits at launch. The emulator does not evaluate IAM policies the way AWS does, and each instance acts as a single account with no cross-account or cross-Region behavior. Devin Pratt, an analyst at IDC, told InfoWorld that it does not yet simulate throttling or outages and does not sandbox the code it runs, GeekWire reported.
Three teams of agents
Goldberg wrote that the emulator is built by three teams of agents running on Amazon Bedrock AgentCore, because agents "have more success on bounded tasks." The first team writes fidelity tests, which are real-world scenarios such as creating an Amazon SQS queue, sending a message, receiving it and deleting the queue. Goldberg said each test is verified against real AWS and the suite now holds tens of thousands of them.
The second team replays those tests against the emulator, groups failures that may share a root cause and files issues. Each issue goes to a single agent on the third team, which traces the cause and edits the code until the issue is fixed.
Every change then has to pass a merge gate. Goldberg wrote that the gate blocks code that does not compile and includes agents that review coding standards and security, along with a check that the change did not lower fidelity. "Without this merge gate, we wouldn't trust what our agents are building," he wrote, adding that hundreds of agents now fix thousands of issues a day.
AWS publishes a fidelity score for each service as a count of passing tests, and the test suite, including tests that still fail, is public on GitHub, according to the AWS News Blog. GeekWire reported that the agents' backlog of known gaps sits in a public folder called "things-that-do-not-work."
From a weekend experiment
The project began as a weekend test inspired by Anthropic's demonstration earlier this year in which a team of Claude agents built a C compiler, GeekWire reported. Goldberg gave Kiro a three-step prompt and got a passable version of SQS in about 15 minutes. By the end of the weekend Kiro had produced a rough version of the rest of AWS, and his team began using it that Monday.
Swami Sivasubramanian, AWS vice president of agentic AI and emerging tech, described the engineer's changing role in a guest post on CTO Werner Vogels' blog. "When agents write the code and check their own work, the engineer's job is to give them room to work on their own," he wrote, along with building the checks that decide when that work is correct.
LocalStack is the best-known alternative. GeekWire noted that it this year put its free version behind an account requirement and limited it to noncommercial use. AWS said it will share more about the project at its re:Invent conference.
Source: About Amazon, “How we built the agents that built AWS Emulator”
Additional sources: AWS News Blog, “Test your applications against AWS locally with AWS Emulator”; GeekWire, “AWS gives developers a free local stand-in for its cloud, built from scratch by AI agents”; All Things Distributed, “AWS Emulator and the engineer's job when agents write the code”
