AWS ships a local emulator for its own APIs: no account, no bill
AWS has published AWS Emulator, a Rust program that mimics its APIs on your machine or in CI, with no AWS account required. You get to test code without watching the meter, provided you can live with a few clearly stated limits.
Testing code that talks to AWS has long required an account, a set of credentials and a strong stomach on invoice day. The AWS Emulator GitHub repository, which surfaced on Hacker News on 11 November 2026, offers something else: a local emulator of the AWS APIs, published under AWS’s own banner, that you run on your laptop, on a dev server or in continuous integration.
An AWS endpoint that never leaves your machine
The idea fits in one sentence: your requests go to the emulator instead of AWS, and you work with emulated resources. The README states that no AWS account is needed and that the tool carries no additional service charges. You only pay for the resources you actually deploy on AWS.
Don’t go looking for a console: there is no graphical interface at all. The emulator serves an endpoint and, once it is running, a few environment variables are enough to point the AWS CLI or an SDK at it. Your code then runs as usual. By default it listens over HTTPS on 127.0.0.1:9297, with a self-signed certificate.
Three ways to run it, one of them by agent
Server mode is the conventional one. On Linux, it installs from an RPM or Debian package. On Windows and macOS, it runs in a container built from a short Dockerfile.
Embedded mode is aimed at tests written in Rust: the emulator is added as a dev dependency and runs in-process, with one isolated instance per test. There is no URL, no certificate and no variable to set, because the emulator’s HTTP client plugs straight into the SDK.
The third route is very 2026: the README suggests installing an aws-emulator skill for a coding agent, then asking the agent to set everything up. That requires AWS CLI version 2.35.0 or later.
A pocket-sized cloud, if your pockets hold 100 GB
The repository is a Cargo workspace with one crate per AWS service, each driven by its Smithy model, with one file per operation and state held in memory. All that tidiness comes at a cost. Building from source, which is only supported on Linux (x86_64 and aarch64), needs at least 100 GB of free disk space for the target/ directory, a figure expected to grow with the number of services.
Embedded mode inherits the tab, because it compiles the emulator into your test binary. Your first cargo test therefore builds the service crates on top of your own code. AWS recommends sharing a single CARGO_TARGET_DIR across projects, caching target/ in CI and pinning the emulator to a release commit.
What the emulator doesn’t claim to do
The README is blunt about its limits. The tool is for building and testing: it must not be used for production, nor for security testing. It doesn’t spell out the list of covered services either. Instead, it points to fidelity scores published with each release, service by service, and to an issues/ directory where missing behaviours are filed under things-that-do-not-work/ before moving to things-that-now-work/ once fixed.
One last thing to know before you launch the binary: telemetry is on by default and sends usage data back to AWS.
So you can now run an entire cloud without getting your credit card out. You’ll just need to clear some room on the hard drive first.
Sources (1)
- AWS emulatorgithub.com
Written with AI assistance from the sources cited above, then reviewed and approved before publication by Sébastien Soulier.
