Atmo
Server-side API mocking for seamless development and testing.
Pricing
Free tier
Flat rate
Adoption
↘CoolingLicense
Open Source
Data freshness
Verified · Jul 12, 2026Overview
What is Atmo?
Atmo is an open-source tool that allows developers to create server-side mocks of APIs, enabling them to test their applications without relying on external services. This makes it easier to develop and test features locally before deploying them.
Key differentiator
“Atmo stands out by offering an open-source solution that can be easily integrated into projects as a library, making it ideal for developers who need server-side API mocking without the overhead of setting up cloud-based services.”
Capability profile
Capability Radar
Honest assessment
Strengths & Weaknesses
↑ Strengths
↓ Weaknesses
API requires Python-specific patterns, TypeScript SDK is community-maintained
v0.1 to v0.2 migration required rewriting chain definitions
Official support is only for Jest and Mocha, lacking popular alternatives like Cypress or Playwright
Mocking complex API interactions can lead to significant slowdowns in test execution times
Fit analysis
Who is it for?
✓ Best for
Teams working with JavaScript or TypeScript who need a reliable way to mock server-side APIs during development and testing phases.
Developers looking for an open-source solution that can be easily integrated into their existing projects as a library.
✕ Not a fit for
Projects requiring cloud-based API mocking services, as Atmo is designed for local use.
Teams working with languages other than JavaScript or TypeScript, as support is limited to these languages.
Cost structure
Pricing
Free Tier
Available
Open source — free to use
Starts at
$0
Model
Flat rate
Enterprise
None
Performance benchmarks
How Fast Is It?
Ecosystem
Relationships
Integrations
Next step
Get Started with Atmo
Step-by-step setup guide with code examples and common gotchas.