AWS Emulator: Over 200 AWS Services Simulated Locally

AWS provides a local emulator for the APIs of over 200 services, usable without an account and at no cost. Its code has been entirely produced by AI agents, and its fidelity is published by version with detailed scores by service and scenario.

Published Fidelity and Release Cadence

AWS publishes a score file with each version. For version 1.0.322, released on November 11, 2026, 24,243 tests out of 42,857 are validated, corresponding to 56.6%, and 80 tests are ignored. Regarding the steps, 49,810 out of 68,007 succeed, which is 73.2%, while 2,752 inter-service flows out of 6,569 succeed, or 41.9%. Results vary by service: KMS achieves 93.9% (291 out of 310), SQS 89.8%, while CloudFormation peaks at 15.8% (414 out of 2,612). Among major services, S3 stands at 79.1%, DynamoDB at 77.3%, SNS at 73.9%, Lambda at 46.4%, and EC2 at 41.5%. Versions 1.0.265 to 1.0.322 were released between November 8 and 11.

Usage Scope and Technical Limitations

AWS Emulator targets local loops and continuous integration and is not intended for security or load testing. IAM evaluation is not implemented, and policies are not interpreted as they are on AWS. The tool operates with a single region and a single account, accepts any identifier but does not isolate resources by them. The verification took place in us-west-2 and, for global services, in us-east-1. In memory and ephemeral, it is not tested for long executions, with an --idle-timeout option for shutdown. Telemetry is enabled by default and can be disabled via a flag, an environment variable, a configuration file, or the built-in API. Unimplemented operations return HTTP 501. According to the fidelity documentation, control APIs correspond better than data APIs, and support for CloudFormation, Terraform, and CDK varies by service.

A Project Entirely Written by AI Agents

The code for AWS Emulator has been entirely written and corrected by autonomous agents. The initiative began with a request to Kiro, who provided a satisfactory Amazon SQS emulator in about fifteen minutes. AWS entrusted the continuation of development to three distinct groups of agents: test creators who design scenarios from Smithy models and validate them on AWS, agents responsible for detecting issues who run these tests on the emulator and report failures, and correcting agents who handle issues individually. Each modification goes through a merge step encompassing compilation, code review, security checks, and fidelity control, with adversarial checks performed by several agents specialized in security. Matthew Goldberg reports hundreds of agents working in parallel and correcting thousands of issues daily. The pipeline relies on AWS Developer Tools with CodeCommit as the repository for the agents, before a final release on GitHub.

Local Setup and Test Integrations

The emulator can be used without an account and at no cost, redirecting the AWS CLI and SDKs to its endpoint. The program, without a graphical interface, is configured via environment variables without modifying application code, and resources disappear upon shutdown. Installation is possible via RPM or Debian packages on Linux, or via a Docker container on macOS and Windows limited to 2 GiB of memory. In integrated Rust mode, it is added as a development dependency for an isolated instance per test, and a skill addition is planned for coding agents with AWS CLI 2.35.0 or later. Building from source allows the use of HTTPS on 127.0.0.1:9297 with a self-signed certificate, requires a Rust toolchain, a C compiler, and at least 100 GB of disk space, and the integrated mode only requires this process for the first cargo test. The documentation provides a fidelity example with DynamoDB, where a table named with two characters triggers the same ValidationException as on AWS.

Coverage of 200+ Services and Platform Features

AWS Emulator relies on 438 API models and covers over 200 services, with a Rust crate for each service. Its default endpoint is HTTPS on 127.0.0.1:9297, and the publisher releases fidelity scores by version. The tool is free and licensed under CC0 for this scope of services, and its coverage exceeds, according to the comparison table, the ranges announced by commercial solutions based on their plans.

Compared to LocalStack, Moto, and Floci, Different Choices

AWS Emulator is distributed under CC0 1.0 license, while Moto is under Apache-2.0 and Floci under MIT, both free. LocalStack offers paid plans with a Hobby tier at $0, a Base plan at $39, and an Ultimate plan at $89 per license per month annually, and requires a provider token. In terms of coverage, AWS Emulator claims over 200 services and 438 API models, while LocalStack indicates 30+, 55+, or 110+ depending on the plan. Default listening points differ: 127.0.0.1:9297 in HTTPS for AWS Emulator, 4566 for LocalStack and Floci, 5000 for Moto. Moto offers a Python testing mode via @mock_aws. Floci self-reports around 13 MiB at rest and about 24 ms at startup. Only AWS Emulator publishes fidelity scores by version among these tools.