AWS SAM CLI is an open-source command-line tool for building, testing, debugging, and deploying serverless applications on AWS, aimed at developers and teams working with Lambda functions, Step Functions, API Gateway, and related services.

What it is

AWS SAM CLI is the command-line interface for the AWS Serverless Application Model. It is written in Python, licensed under Apache-2.0, and lives in the AWS serverless ecosystem alongside Lambda, Step Functions, API Gateway, EventBridge, SQS, and SNS. It provides a Lambda-like execution environment so that serverless applications can be built, tested, debugged, and deployed from a terminal or a CI/CD pipeline. The homepage sits at aws.amazon.com/serverless/sam, with installation and quick-start documentation in the AWS Serverless Application Model developer guide.

The concrete problem it solves is the gap between writing function code and getting it running. Before the CLI, teams assembled their own Makefile workflows to compile and package Lambda functions and then managed CloudFormation template deployment by hand. SAM CLI replaces those ad-hoc workflows with named commands: sam build compiles, builds, and packages Lambda functions for both zip and image function types, using provided runtimes or custom Makefile workflows, and sam deploy handles deployment of SAM and CloudFormation templates. The same toolchain covers the local and the cloud end of the loop, so packaging logic is not rewritten per project.

Key capabilities

• sam init initializes serverless applications in minutes from AWS-provided infrastructure templates.
• sam build compiles, builds, and packages Lambda functions with provided runtimes and custom Makefile workflows, for zip and image function types.
• sam local commands test a Lambda function and API Gateway locally inside a Docker container, working with both SAM and CDK applications.
• sam sync syncs and tests changes in cloud developer environments, the workflow behind SAM Accelerate.
• sam deploy deploys SAM and CloudFormation templates.
• sam pipeline init creates CI/CD pipelines from prebuilt templates for popular CI/CD systems.
• sam logs and sam traces tail CloudWatch logs and X-Ray traces.

Who uses it and how

• Serverless developers assembling applications from Lambda functions, Step Functions, API Gateway, EventBridge, SQS, and SNS.
• Teams running CDK applications that use sam local for local Lambda and API Gateway testing rather than deploying to check behaviour.
• Developers using SAM Accelerate and sam sync to test incremental changes directly in a cloud developer environment, including work with nested stacks.
• Node and TypeScript teams building with esbuild, a workflow documented in the project's blog posts.
• Platform and application teams that need CI/CD from sam pipeline init instead of hand-written pipeline definitions.

Getting started

Install through Homebrew with the tap aws/tap/aws-sam-cli or through pip with the package aws-sam-cli; the README points to the official installation page and a "Hello World" web app quick start for the first build and deploy.

How it compares

No paid products that this project replaces are listed in the facts, and no similar tools are named. Among the adjacent tooling that is named, SAM CLI sits alongside AWS CloudFormation and the AWS CDK rather than competing with them: it consumes SAM and CloudFormation templates and tests CDK applications locally. On that basis it stands alone in this registry as the AWS-specific CLI for serverless build, local test, and deploy workflows.

When to use it — and when not to

Local testing requires Docker, deployment and sync require AWS credentials and live cloud resources, and adopting the tool means committing to the SAM and CloudFormation template model, so teams running on other clouds or avoiding CloudFormation should look elsewhere. The project carries 535 open issues, which is worth weighing against its Apache-2.0 licence and its recent commit activity. The README is oriented toward AWS documentation and workshops, so expect to follow external links rather than learn everything from the repository alone.