Best Free API Testing Tools for Developers: Postman, Hoppscotch, and Thunder Client Compared
A backend developer I know recently opened Postman to send a single GET request to a local endpoint. Before the request went out, the app prompted her to sign in, sync her workspace to the cloud, and dismiss a banner about the platform’s AI features. The request itself took two seconds. Getting to it took closer to two minutes.
That small friction is why the free API testing market has become more interesting than it used to be. Postman is still the default choice for millions of developers, but two challengers—Hoppscotch, a browser-based tool with an open-source core, and Thunder Client, a VS Code extension—have built loyal followings by stripping away account requirements and desktop bloat. All three have genuinely capable free tiers. The right pick depends on how you work, not on which one has the longest feature list.
Why API testing tools matter more than ever
API testing isn’t a niche activity anymore. According to Postman’s own State of the API report, survey respondents manage an average of around 26 APIs each, and most organizations describe their API footprint as growing rather than shrinking. Whether you’re debugging a REST endpoint, validating a GraphQL query, or wiring up a webhook, you need a fast way to send requests, inspect responses, and save the ones you use repeatedly.
The free tiers of the three tools below cover the vast majority of day-to-day needs: sending HTTP requests, managing environments and variables, organizing collections, and writing basic test scripts. The differences show up in architecture, resource usage, collaboration limits, and how much of your workflow lives inside the tool versus outside it.
Postman: the incumbent with the deepest feature set
Postman is the tool most teams standardize on, and the free plan is still substantial. You get unlimited personal workspaces for individual use, a generous cap on saved requests and collection runs, and the full request builder with support for REST, GraphQL, WebSocket, gRPC, and more. Features that once required a paid plan—like the Collection Runner and basic mock servers—are usable within free-tier limits, though monthly quotas apply.
The strengths are real. Postman’s scripting environment (built on a sandbox with pm.* APIs) is the most mature in the category, and the ecosystem of public API collections and documentation is unmatched. If you’re onboarding onto a third-party API, chances are someone has published a Postman collection you can import in seconds.
The trade-offs are equally real. Postman is an Electron desktop app, and it feels like one—memory usage is heavy compared to a browser tab or a lightweight editor extension. The free tier now pushes cloud sync and account sign-in, and some collaboration features (shared workspaces with larger teams, certain roles) sit behind the paid plans. For solo developers, none of this is disqualifying, but it explains why so many have gone looking for alternatives.
Hoppscotch: lightweight, browser-first, open source
Hoppscotch (formerly Postwoman) started as an open-source project and still leads with that identity. The core is available on GitHub under an MIT license, and the hosted web app at hoppscotch.io lets you send requests without creating an account. Open the site, type a URL, hit send. That’s the entire onboarding.
For developers who care about speed and footprint, the difference is noticeable. Hoppscotch runs in a browser tab and loads fast; there’s also a desktop build and a CLI. It supports REST, GraphQL, WebSocket, Server-Sent Events, MQTT, and Socket.IO, which covers more protocols than most people need. Collections, environments, and pre-request/test scripts are all available, and the scripting API is familiar enough that migrating simple Postman collections is usually straightforward.
The free hosted tier has limits worth knowing about. Collections and history are stored locally in your browser unless you sign in, and the cloud-synced free plan caps the number of collections and shared workspace members. Team collaboration features—shared collections with granular permissions, for example—are part of paid plans. Self-hosting the open-source version removes most of these caps if you’re willing to run it yourself, which is a genuine option for teams with privacy requirements.
Hoppscotch’s interface is cleaner and less cluttered than Postman’s, though that simplicity cuts both ways: advanced scripting and some enterprise-oriented features are less developed.
Thunder Client: API testing inside VS Code
Thunder Client takes a different approach entirely. It’s a VS Code extension, which means your API testing lives in the same window as your code. For developers who already spend their day in the editor, that’s the whole pitch—no app switching, no separate login, no second Electron process competing for RAM.
The free version covers the essentials well: HTTP requests, collections stored as local files, environments, basic testing with a scripting syntax similar to Postman’s, and GraphQL support. Because collections can live in your workspace, they can be committed to version control alongside your code, which some teams find preferable to cloud-hosted collections.
The constraints are the flip side of the design. Thunder Client is fundamentally a single-user, local-first tool; real-time collaboration and cloud sync are paid features, and the free tier limits some advanced capabilities like certain CLI and CI integrations. It’s also VS Code-only—if you use JetBrains IDEs or Vim, it’s not an option. And while it handles everyday REST work smoothly, it’s less suited to heavy protocol testing or large-scale collection runs than Postman.
How the three compare at a glance
| Postman | Hoppscotch | Thunder Client | |
|---|---|---|---|
| Form factor | Desktop app (Electron), web | Browser app, desktop, CLI | VS Code extension |
| Account required (free) | Sign-in pushed; limited guest use | No for local use | No |
| Open source | No | Yes (MIT core) | No |
| Protocols | REST, GraphQL, gRPC, WebSocket, more | REST, GraphQL, WebSocket, SSE, MQTT, Socket.IO | REST, GraphQL |
| Scripting | Most mature (pm.* sandbox) |
Yes, Postman-like | Yes, Postman-like |
| Collaboration (free) | Limited | Limited | Local only |
| Resource footprint | Heavy | Light | Light (shares VS Code) |
| Best for | Broad feature needs, team standards | Quick requests, privacy-minded users | Editor-centric solo work |
Which one should you actually use?
The honest answer is that many developers end up using more than one. A common pattern: Thunder Client for quick requests while coding, Hoppscotch for sharing a request with a colleague who doesn’t have Postman installed, and Postman for collection runs, documentation, or working with third-party API collections.
If you’re choosing a primary tool, start from your constraints. Need the widest protocol support and the most mature scripting? Postman’s free tier is hard to beat, provided you can live with the account prompts and memory use. Want something fast, open source, and usable without sign-up? Hoppscotch is the strongest fit, especially if self-hosting appeals to you. Already live in VS Code and mostly test your own APIs? Thunder Client keeps everything in one window with minimal overhead.
The takeaway
The free tiers of all three tools are capable enough for professional work; the decision is less about features than about where you want your API testing to live. Postman offers depth and ecosystem at the cost of weight and account friction. Hoppscotch offers speed and openness with lighter collaboration features. Thunder Client offers tight editor integration with a local-first, single-user model. Try each against a real endpoint from your current project—the tool that gets out of your way fastest is usually the right one.