Introduction
A modern, free, and open-source API laboratory for designing, testing, and debugging API workflows.
Welcome to Yasumu
Yasumu is a modern, free, and open-source API laboratory for designing, testing, and debugging API workflows. Built for developer productivity, speed, and freedom — without vendor lock-in.
Beta Software
Yasumu is actively under development. You may encounter unfinished features, bugs, or inconsistent behavior as we rapidly prototype and iterate. We welcome your feedback and contributions!
Why Yasumu?
Unlike traditional API clients that store data in hidden databases or require cloud accounts, Yasumu operates like an IDE for your APIs. Your configurations live directly in your project folder, making collaboration and version control seamless.
It feels like the tools you already know, but with the flexibility to handle complex, experimental workflows directly in your file system.
What Makes It Different
Everything lives in your project folder as plain .ysl files. Commit
them, diff them, review them in PRs—your API collections are just
another part of your codebase.
The app runs on Tauri with an embedded custom JavaScript runtime
powered by Deno. This handles everything from request execution to
scripting—write your pre-request logic in TypeScript without
external tooling. You can also run .ysl files directly from the terminal
for CI/CD integration.
No account required. No cloud sync. No paid tiers.
Protocol Support
Yasumu is evolving to become a protocol-agnostic powerhouse.
| Protocol | Status | Notes |
|---|---|---|
| REST API | ✓ | Full HTTP/HTTPS request support |
| Catch-all SMTP | ✓ | Integrated local email server for testing |
| GraphQL | — | In development |
| WebSocket | — | In development |
| Server-Sent Events | — | In development |
| Socket.IO | — | In development |
| Plugins API | — | In development |
Concepts & Workflow
Yasumu acts as an IDE for your API interactions. Unlike tools that hide data in proprietary databases or cloud silos, Yasumu lives in your repo.
Project-Based Workspaces
When you initialize Yasumu in a project, it creates a yasumu
directory. Your definitions, tests, and workflows are stored here
using the Yasumu Schema Language (.ysl) — a custom format designed
for readability and clean git diffs.
Collaboration via Git
- Commit & Push: Treat your API collections as code.
- Review:
.yslfiles are text-based, making Pull Request reviews easy. - Sync: Teammates simply pull the branch to get the latest API workflows.
- Secure: Sensitive secrets are managed via local environment variables, never committed to version control.
Runtime Architecture
Tauri provides the desktop shell and OS-level operations. The
backend—request execution, scripting, and core logic—runs on an
embedded custom JavaScript runtime built on deno_runtime.
Quick Start
Tech Stack
- Frontend: Next.js with React
- Desktop Shell: Tauri
- Backend Runtime: Embedded custom JS runtime powered by Deno
- Platforms: Windows, Linux, macOS
Project Philosophy
- Open Source by Default — Transparency builds trust. The entire codebase is available on GitHub.
- Zero Vendor Lock-in — Your data belongs to you, stored in readable files on your disk.
- Developer Experience First — Fast, beautiful, and keyboard-friendly.
- No Artificial Paywalls — All features are free to use.
- Sustainability — Built for long-term maintainability over hype.
License
Yasumu is developed by Neplex and is licensed under the AGPL-3.0 license.