Best Open Source API Testing Tools Compared: Hoppscotch vs Bruno vs Thunder Client
Postman’s 2023 decision to retire its Scratch Pad and push users toward cloud-synced collections triggered a quiet migration across the developer community. Within months, GitHub stars for API client alternatives climbed sharply, and three names kept surfacing in the same threads: Hoppscotch, Bruno, and Thunder Client. All three are open source, all three handle the core job of sending HTTP requests and inspecting responses, but they take fundamentally different approaches to where your data lives, how you collaborate, and what “open source” actually means in practice.
This comparison breaks down how each tool works, where each one shines, and which trade-offs matter depending on how you test APIs.
The Contenders at a Glance
| Feature | Hoppscotch | Bruno | Thunder Client |
|---|---|---|---|
| License | MIT | MIT | MIT |
| Form factor | Web app + desktop + CLI | Desktop app (Electron) | VS Code extension |
| Storage model | Cloud sync or self-hosted | Local files (plain text) | Local VS Code storage |
| Git-friendly | Via export | Native (files in repo) | Limited |
| Self-hosting | Yes (Docker) | N/A (local-first) | N/A |
| Free team collaboration | Limited | Via Git | No |
| Best for | Teams wanting a hosted or self-hosted web client | Developers who want APIs versioned alongside code | VS Code users who want zero context-switching |
Hoppscotch: The Web-First Option
Hoppscotch started life as a lightweight browser-based alternative to Postman, and that origin still shapes everything about it. You can open the hosted app, paste a URL, and send a request within seconds—no install, no account required for basic use. It supports REST, GraphQL, WebSocket, SSE, and MQTT, which is broader protocol coverage than either competitor offers out of the box.
The bigger differentiator is deployment flexibility. Hoppscotch ships as a self-hostable application, so teams with data residency requirements or strict security policies can run the entire stack inside their own infrastructure. The project provides Docker images and a CLI, and the self-hosted tier includes team workspaces, shared collections, and environment management without a per-seat cloud bill.
The trade-off is that Hoppscotch’s collaboration story is its cloud service. If you use the hosted version, collections live on Hoppscotch’s servers. If you self-host, you own the infrastructure—which is more operational overhead than most individual developers want. The desktop app exists and works offline, but the product’s center of gravity is clearly the web experience.
Choose Hoppscotch if: you want a browser-accessible client, need self-hosting for compliance reasons, or work with protocols beyond plain REST.
Bruno: The Git-Native Contender
Bruno made its name with a single design decision: collections are stored as plain-text files on your filesystem, not in a proprietary database or a cloud account. Each request is a .bru file you can read, diff, and commit. That means your API tests live in the same repository as the code they test, and code review covers both.
This is a genuinely different philosophy from Postman’s model, and it solves a real problem. When an endpoint changes, the request definition changes in the same pull request. There’s no export-import dance, no risk of a colleague’s local collection drifting from what’s in version control. Bruno also supports a scripting layer using JavaScript for pre-request and post-response logic, plus a CLI (bru) for running collections in CI pipelines.
Bruno’s limitations are mostly about scope. It’s a desktop application—there’s no browser version and no hosted collaboration service. Team workflows depend entirely on Git, which is elegant if your team already lives there and awkward if it doesn’t. The ecosystem of plugins and integrations is smaller than Postman’s, and while the core feature set is solid, some advanced enterprise features (SSO, audit logs, role-based access) aren’t part of the free open-source product.
Choose Bruno if: you want API collections versioned in Git, you value offline-first local storage, or you’re already running tests in CI.
Thunder Client: The VS Code Native
Thunder Client takes the opposite approach from both: instead of a standalone app, it’s an extension that lives inside VS Code. If you already spend your day in the editor, this eliminates an entire application from your workflow. Requests, responses, and environment variables all appear in the sidebar next to your file tree.
The extension is fast and lightweight compared to Electron-based clients, and the free tier covers most individual needs: collections, environments, request chaining, and basic test assertions. It also integrates with VS Code’s theme and keyboard shortcuts, which sounds trivial until you’ve spent a week context-switching between an editor and a separate API client.
The constraints are structural. Thunder Client is tied to VS Code—if you use JetBrains IDEs, Neovim, or anything else, it’s not an option. Collections are stored in VS Code’s local storage rather than as portable files, so Git-based collaboration requires export/import rather than direct commits. Team features like shared collections and collaboration exist, but they’re part of a paid tier. And because it’s an extension, it inherits VS Code’s resource limits and can’t match a dedicated app for very large test suites.
Choose Thunder Client if: VS Code is your primary editor and you want the lightest possible setup for individual API testing.
How to Decide
The three tools aren’t really competing on features—they’re competing on architecture, and that’s what should drive your choice.
Start with where your data should live. If API definitions belong in version control alongside application code, Bruno is the clear answer. If they should live in a shared cloud workspace your team can access from anywhere, Hoppscotch’s hosted or self-hosted options fit better. If they’re personal scratch work tied to your editor, Thunder Client is sufficient.
Then consider your protocol needs. Hoppscotch covers GraphQL, WebSocket, SSE, and MQTT in addition to REST. Bruno and Thunder Client focus primarily on REST and GraphQL. If you’re testing real-time APIs, that narrows the field quickly.
Finally, weigh collaboration honestly. A solo developer testing endpoints locally has different requirements than a five-person team that needs shared environments and review workflows. Bruno’s Git model is powerful but assumes Git fluency. Hoppscotch’s self-hosted tier gives you control but requires someone to run the servers.
A Practical Note on Migration
All three tools can import Postman collections, so switching costs are lower than they look. A reasonable approach: export your existing Postman collections, import them into whichever tool you’re evaluating, and run your most-used requests for a week before committing. The friction points—environment variable syntax, scripting APIs, test assertion formats—only become obvious through daily use.
The Takeaway
There’s no single winner here, and that’s the point. Hoppscotch wins on protocol breadth and deployment flexibility. Bruno wins on version control integration and data ownership. Thunder Client wins on convenience for VS Code users. The right choice depends on whether your priority is collaboration infrastructure, Git-native workflows, or staying inside your editor—and for many teams, the honest answer is that all three are good enough that the decision comes down to which one fits the workflow you already have.