Announcement

AWS says agents wrote its free local emulator—and humans didn’t review the code

The free tool lets developers test AWS APIs locally, but passing on your laptop isn’t a production permission slip.

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AWS gives developers a free local stand-in for its cloud, built from scratch by AI agents

TLDR

AWS launched a free local API emulator and says agents wrote all its code without human code review. The agents also test and maintain it, while engineers design their controls. AWS describes coverage spanning more than 200 services, though how closely it matches AWS varies by service and feature. It’s a place to test—not proof an app is production-ready: AWS warns against using it for security testing or production workloads.

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What actually runs locally

AWS describes the emulator as built from more than 400 API models covering more than 200 services. Those models describe the operations, inputs, outputs and errors that applications use to communicate with AWS. How closely the emulator matches AWS varies by service and feature, the company says. Source Source

Existing AWS command-line tools and software development kits can target the emulator’s local endpoint through environment variables, without rewriting application code to redirect the requests. Source Source

The Rust-based tool installs through RPM or Debian packages on Linux. On macOS and Windows, users build a Docker image using AWS’s Dockerfile; AWS doesn’t supply a ready-made image. An embedded mode also supports tests using the AWS SDK for Rust. Source

Offline testing is supported, although anonymous usage and error telemetry is enabled by default and can be disabled. Local testing doesn’t incur AWS resource charges; deploying to actual AWS still does. Source Source

Agents write the code; engineers build the gates

Goldberg describes three agent teams with separate jobs. One develops test scenarios from AWS’s public API models and verifies them against real AWS. Another runs those tests against the emulator and files issues when the behavior differs. A third fixes individual issues. The answer key is still the real cloud. Source

AWS says proposed changes must pass an automated merge gate, including compilation, coding-standard reviews, security reviews by other agents and checks that the change hasn’t made the emulator less faithful to AWS. Source

Swami Sivasubramanian, writing in a guest post on Werner Vogels’ blog, describes engineers building specifications, tests and merge gates, including deterministic checks that prevent agents from touching code outside their assigned boundaries. Source

Goldberg says an earlier version of the agents decided to build their own Python interpreter to support Lambda functions. The team subsequently instructed them to reuse existing libraries. Apparently, that advice still needs saying when the programmer is software. Source

AWS says the source code and fidelity tests are available on GitHub, with the emulator code released under CC0, a public-domain dedication. But public code doesn’t mean human patches are welcome: AWS’s Tom Callaway told The New Stack that the project will accept customer issues, not pull requests. Source Source Source

A passing test still has limits

AWS publishes per-service fidelity scores as passing tests out of total tests. The test suite is also public, including scenarios the emulator doesn’t pass yet. Source

AWS’s documentation says the emulator doesn’t evaluate Identity and Access Management policies or resource-based policies the way AWS does. A request that real AWS would deny might succeed locally. Each emulator also acts as a single account, without cross-account or cross-Region behavior, and its in-memory resources disappear when it stops. Source Source

IDC research director Devin Pratt also told InfoWorld that the emulator doesn’t sandbox the code it executes. AWS separately instructs users to keep real credentials out of test environments and test their security settings and complete application on AWS before production. Source Source