AWS SAM CLI Supports CloudFormation Language Extensions for Efficient Local Serverless Development

AWS SAM CLI added support for CloudFormation Language Extensions, enabling developers to write less repetitive infrastructure code while locally iterating serverless applications.

By Elena Parker · Editorial pseudonym · 2026-05-18 · 1 min read

AI-ASSISTED REPORTING · RETROSPECTIVE ARCHIVE

Retrospective edition: 2026-05-18. Source published: 2026-05-18. Added to this archive: 2026-11-03. This briefing was prepared later from the linked announcement; it was not published on this website on the historical edition date.

Previously, templates using Language Extensions could not run locally in SAM CLI, forcing developers to choose between reduced template duplication and local testability. Now, SAM CLI processes these extensions in memory during local workflows, preserving original templates for cloud deployment.

This update supports transforms like Fn::ForEach and conditional attributes, streamlining local development workflows such as sam build, sam local invoke, and sam sync. It reduces deployment errors and accelerates iteration cycles by catching issues before cloud deployment without sacrificing Infrastructure as Code maintainability.

Source & further reading

AWS SAM CLI adds AWS CloudFormation Language Extensions support to accelerate local serverless development ↗

Source published 2026-05-18. This report was prepared with AI assistance from the linked primary-source material. Claims and limitations should be checked against the original announcement or research.