WebMCP: an interface for Web agents
WebMCP proposes a way for a Web page to expose some interface functions as agent-callable tools. As of November 12, 2026, its specification is a Community Group draft, not a W3C Standard.
Describe reusable functions
A developer can describe a JavaScript function with a name, description and input schema. The goal is to reduce reliance on agents guessing every action from buttons and pixels.
Proposed is not universally supported
A published draft does not mean all browsers or agents implement the API. Deployments need conventional Web fallbacks and must test supported implementations.
Authorization and user experience
Exposing a tool should not grant an agent rights to place orders or edit data without consent. Inputs require validation and sensitive operations must remain visible and controllable.
Learning example
A catalog interface could expose a document filtering function. It should preserve keyboard-accessible search for human visitors.
Project status and API boundaries
WebMCP explores exposing page functionality as tools callable by browser agents. The Web Machine Learning Community Group document is a community draft, not a W3C Recommendation. Distinguish the imperative JavaScript API from declarative form-based explorations. Actual browser support must be tested.
Exercise: accessible reversible filter
On an encyclopedia page, choose language and category filtering as the proposed action. Define input parameters, keep ordinary HTML controls usable without an agent and make the result visible. Avoid deletion or data submission in the demonstration. Identify features supported by an experimental browser versus conceptual simulation.
Core steps
- 01Describe a function
- 02Define inputs
- 03Verify permission and fallback
- 04Test with and without agents
Three questions to ask
Is its community draft status clearly stated?
Can a human still use the service without an agent?
Which actions require confirmation?
Read the source documents
Versions, reuse terms and document status can change. Check them on the original sites.