Liha WebMCP Adapter

Inspiration

WebMCP is powerful, but most existing websites will not implement it overnight. We wanted an adoption layer that works today while giving site owners a path toward native WebMCP tomorrow.

What it does

Liha WebMCP Adapter adds inspectable WebMCP tools to sites that have not implemented WebMCP themselves—without modifying the target website. People can install declarative adapters from the Liha Adapter Store, or record a real workflow once in Adapter Studio and turn it into a reusable tool.

Agents discover named tools with JSON input schemas through WebMCP and invoke them like native tools. The runtime drives the site's real UI; it does not rely on screenshots or guessed selectors.

How we built it

A Manifest V3 Chrome extension injects a small runtime only into exact approved origins and registers tools through document.modelContext. Adapter JSON is validated against a closed schema. The recorder captures DOM intent, Studio turns recordings into parameterized steps, and the runtime replays them against the live UI. React and TypeScript power the extension, demos, and Store; Cloudflare hosts the public app.

Safety by design

Adapters are plain JSON with a closed step vocabulary: no scripts, no eval, and no wildcard origins. Users inspect origin, capability, selectors, and visible effects before installation. Ambiguous selectors fail closed. WRITE and DESTRUCTIVE actions can require explicit confirmation. Community adapters are submitted through public GitHub pull requests for review.

Challenges

The hardest part was preserving WebMCP's structured-tool model without creating an arbitrary-code channel. We also handled selector ambiguity, page-specific health states, React controlled inputs, confirmation gates, recording real workflows, and genuine out-of-page WebMCP invocation.

Accomplishments

The demo closes the full loop: discover an adapter, inspect permissions, install it, expose tools through WebMCP, invoke them from outside the page, record a new workflow, validate it, and install the resulting custom tool. A site with zero WebMCP code becomes agent-ready in minutes.

What we learned

Adoption and safety are the same design problem. Community tooling only scales when people can understand exactly where a tool runs and what visible actions it performs.

What's next

We will expand community coverage, add verified signing and version updates, improve multilingual registry metadata, and help site owners graduate popular adapters into native WebMCP implementations.

Built With

• chrome
• manifest
• typescript