WebMCP vs agents.json
Product engineer: agents.json documents an API; WebMCP wraps page actions. Developer-platform lead: agents.json is at 0.1.0; WebMCP has browser vendors behind it. Agent builder: Neither is required by MCP clients today. WebMCP exposes JavaScript tools in the page at run time; agents.json is a static OpenAPI-based file at /.well-known/agents.json describing API flows.
The sourced difference
WebMCP exposes JavaScript tools in the page at run time; agents.json is a static OpenAPI-based file at /.well-known/agents.json describing API flows. (WebMCP: webmachinelearning/webmcp, read 5 November 2026; agents.json: wild-card-ai/agents-json, observed on 4 November 2026 and wild-card-ai/agents-json, read 5 November 2026)
Verdicts by reader
| Reader | Verdict |
|---|---|
| Product engineer | agents.json documents an API; WebMCP wraps page actions. |
| Developer-platform lead | agents.json is at 0.1.0; WebMCP has browser vendors behind it. |
| Agent builder | Neither is required by MCP clients today. |
Side by side
| Aspect | WebMCP | agents.json |
|---|---|---|
| Maintainer | W3C Web Machine Learning Community Group (editors from Microsoft and Google) | Wildcard AI (started the project); maintainers listed in MAINTAINERS.md |
| What it is | A browser API that lets a page register JavaScript functions as tools, with descriptions and schemas, that an in-browser agent can call. | An OpenAPI-based contract that describes flows (sequences of API calls) and links between actions so agents can call an API correctly. |
| Status and version | Draft specification; Chrome and Edge test it in an origin trial, Brave behind a flag, no Firefox or Safari implementation (nekuda FAQ, October 2026). | Version 0.1.0, MIT licence; proposed location /.well-known/agents.json. |
| What it does not do | Does not work without a browser agent that reads the page; does not replace a server-side MCP endpoint; the declarative form-based API is only being explored. | Does not define transport or auth beyond OpenAPI; not referenced by the MCP spec. |
Read the full entries: WebMCP and agents.json.
Seen in the shared crawl
The shared crawl looks for WebMCP in the initial HTML of each home page. It found a WebMCP hint on 25 of 7,545 home pages in the Tranco top 10,000 and on 59 of 3,393 on Ora's leaderboard.
| Path | Top 10,000 found | Ora leaderboard found |
|---|---|---|
/agents.json | 0 of 7,485 (0%) | 0 of 3,366 (0%) |
A path counts only when the answer is the right kind of document. Many sites answer these paths with an ordinary web page, which is not counted. See the census.