head to head · open source
Harness vs extension.js
Harness has 38,378 GitHub stars, 3,397 forks, 106 open issues and last shipped 2 days ago. extension.js has 5,159 stars, 139 forks, 7 open issues and last shipped yesterday. Harness leads on adoption by 644% (38,378 vs 5,159 stars). Harness is written in Go under Apache-2.0; extension.js is written in TypeScript under MIT. Harness has attracted 9% as many forks as stars, extension.js 3%. extension.js was the more recently maintained of the two, and both are self-hostable with no licence fee.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| Harness | extension.js | |
|---|---|---|
| GitHub stars | ★ 38K | ★ 5.2K |
| License | Apache-2.0 | MIT |
| Written in | Go | TypeScript |
| Last push | 2026-09-16 | 2026-09-17 |
| Forks | ⑂ 3.4K | ⑂ 139 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick Harness if
- You weight community size — 38K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches Go
- You value the larger contributor base for long-term maintenance
pick extension.js if
- You want the extension.js feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches TypeScript
- You evaluated both and extension.js fits your workflow better
About Harness
Harness Open Source is an Apache 2.0, Go based developer platform that combines Git source control management, CI/CD pipelines, Gitspaces hosted development environments and artifact registries into one self hostable system for engineering teams that want end to end software delivery without stitching four separate products together.
read the full Harness overview →
About extension.js
extension.js is an open source cross browser extension framework written in TypeScript under the MIT license. It targets Chrome, Edge, Firefox, and Safari, and it lets developers build extensions without a separate build configuration for each browser.
read the full extension.js overview →
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Frequently asked questions
Is Harness or extension.js more popular?
Harness has 38,378 GitHub stars and extension.js has 5,159. Harness has the larger community by that measure.
Are Harness and extension.js free?
Both are open source. Harness is licensed under Apache-2.0 and extension.js under MIT. Neither carries a licence fee.
What is the difference between Harness and extension.js?
Harness is written in Go and extension.js in TypeScript. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, Harness or extension.js?
Choose Harness if you want the larger community (38,378 stars) or its Apache-2.0 licence terms. Choose extension.js if its feature set, stack or MIT licence fits better. Both are self-hostable.