onUI
onUI lets users annotate web interfaces and export structured context for AI agents.
About onUI
onUI is a browser extension for Chrome, Edge and Firefox that lets users annotate or draw on any web interface and export structured context for AI agents, without changing the application's code. Annotations are made per tab, which is off by default, through an in-page dialog that records intent and severity, or through a draw mode for rectangular and elliptical regions. Output can be copied in compact, standard, detailed or forensic formats.
A local MCP server and native bridge connect the extension to MCP-compatible clients, and installation can be done through browser store listings or a one-command installer that can also set up MCP. The local MCP bridge requires Node 20 or later, and Firefox installation is done manually from a release artifact as a temporary add-on.
Key features
- Per-tab annotation toggle, off by default
- In-page dialog recording intent and severity
- Draw mode for rectangle and ellipse regions
- Shift-click batch selection of multiple targets
- Compact, standard, detailed and forensic output formats
- Local MCP server with native bridge, no cloud backend
Best for: Developers and designers who want to give AI agents specific visual and structural context about a web UI without modifying the application's code.
Good for
- Annotates existing web UIs with no app code changes
- Local MCP server and native bridge described as needing no cloud backend
- Open source repository distributed through Chrome Web Store, Microsoft Edge Add-ons and release artifacts
Watch out for
- Local MCP bridge setup requires Node 20 or later
- Firefox install is manual, loading a temporary add-on from a release artifact
- Chromium unpacked installs require developer mode and a manual load step
onUI at a glance
- Website
- github.com/onllm-dev/onUI
- Category
- Development › Developer Tools
- Type
- Open-source project
- Pricing
- Not confirmed. Check the site
- Open source
- Yes · Source code
- Language
- English
- Last checked
- Oct 6, 2026 · Online when checked
- Listed
- Oct 5, 2026
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onUI FAQ
Does onUI require changes to the application being annotated?
No. The project states that annotations work without app code changes.
Which browsers are supported?
Chrome, Edge and Firefox. Chrome and Edge have store listings; Firefox is installed manually from a release artifact as a temporary add-on.
Does onUI need a cloud service?
The local MCP server and native bridge are described as requiring no cloud backend.
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