The roto book¶

roto is an AWS simulator written in Rust: a from-scratch rewrite of moto's server mode. A single binary serves AWS wire protocols on one port, with persistent SQLite state and S3 object bodies stored as real files.

roto is intended as a replacement for LocalStack for local AWS development, with persistent resources that survive server restarts. Point your AWS clients at its local endpoint, create your development environment once, and keep using its buckets, queues, tables, and other supported resources across sessions.

Core services and optional Lua services¶

roto's core services are hand-tuned in Rust and built into the server binary. These are where we aim to offer a first-class local development experience, with useful service behavior, persistence, and cross-service integration. Most users will start here: typical AWS applications are built on services such as S3, SQS, DynamoDB, Lambda, SNS, and EventBridge. These support everyday application workloads such as storing data, processing messages, and running event-driven code. See core service coverage for the supported behavior and remaining gaps.

The optional Lua services are provided for completeness and mostly offer simple CRUD, metadata storage, and configuration simulation, mainly for service administration rather than everyday application workloads. They have a narrower scope and do not carry the same first-class experience goal. Adding them requires downloading a separate service bundle from a GitHub release and passing --lua-services when starting the server; installing roto-aws alone does not include them. See optional Lua service coverage and bundle installation.

Why an open-source LocalStack alternative¶

LocalStack for AWS is now distributed as commercial software. In March 2026, LocalStack replaced its maintained Community edition with a unified distribution requiring an account and authentication token. Commercial use requires a commercial license; free access remains available for non-commercial use and eligible open-source projects. See LocalStack's distribution announcement and licensing documentation.

For many organizations that want to avoid subscription procurement, license management, and account or token administration for local development and CI, that makes LocalStack an impractical choice. roto is intended to offer an MIT-licensed alternative that runs locally without a vendor account, license key, or subscription.

MiniStack is another open-source LocalStack alternative, with much broader AWS service coverage than roto. MiniStack is also committed to remaining free and open source under the MIT license. roto aims to offer solid support for core AWS services in a dependency-free Rust binary you can drop into a development environment or CI without Docker containers or language runtimes. Check roto's service coverage to see whether it supports your workload. An embedded Lua interpreter lets you create and wire services, define inline Lambda handlers, and intercept AWS requests, without installing a separate Lua runtime.

roto will be free forever. This project has no revenue goal and no interest in monetization. There is no plan for paid tiers, license fees, or a commercial edition. The MIT license lets you use, modify, and redistribute the code, including in commercial projects.

roto is maintained with AI assistance, with the aim of keeping maintenance costs effectively zero. That supports keeping the project free without a revenue model. Changes are still checked through Rust tests and moto compatibility suites.

Why persistence comes first¶

Moto focuses on quick, isolated integration tests with disposable mock state. Its testing documentation describes state being reset between test methods, and the request for server-state persistence was closed as not planned. A persistent local AWS environment is outside that focus.

roto takes moto's server-mode API behavior as a compatibility reference and makes persistence a core part of the design: SQLite stores service state, and S3 object bodies live in real files. The goal is a lightweight local AWS environment you can stop and resume, serving the development role often filled by LocalStack. LocalStack also supports persistence; roto provides its own persistent implementation in a single Rust binary.

For disposable integration tests, roto also offers --ephemeral and reset endpoints. It does not provide moto's in-process @mock_aws mode. Its current service coverage is narrower than LocalStack's; check service coverage before migrating a workload.

Start with Getting started, check service coverage, or read Architecture to work on the implementation.

See Performance for measured startup, idle RSS, and API latency, with a reproducible suite and raw results.

The book also covers Lua setup, the full Lua API reference, runnable demos, integration testing, server options and inspection, and persistent storage. Service guides explain CloudFormation, EventBridge, S3, CloudWatch Logs, Kinesis, KMS, IoT topics and WebSockets, and local Lambda execution. The runtime Lua handler and interception guide covers inline Lambda handlers and request interceptors.

Project maturity¶

roto is under active development. It implements a growing set of services, with substantial differences in coverage. Credentials are tracked for account routing, but signatures and IAM policies are not enforced. Stored policies and ACLs do not imply access checks.

The repository's STATUS.md is the detailed coverage baseline. PLAN.md contains design goals and future work; planned features are not necessarily implemented.

License¶

roto is MIT licensed. Vendored moto tests and botocore service models carry Apache-2.0 notices; see the repository's NOTICE.