Webmcp Browser Agent Declarative Api Poc 2026

Date: 2026-05-20
Track: sandbox-poc
Slug: webmcp-browser-agent-declarative-api-poc-2026
Environment: Python 3.12.x (local), Chrome 145+ required for live agent interaction

Experiment

Created a minimal WebMCP-annotated HTML file demonstrating both the Declarative API (HTML form attributes) and the Imperative API (navigator.modelContext.registerTool()). Validated the declarative tool structure by parsing the HTML locally with Python's html.parser module.

Commands Run

# Create annotated HTML demo
cat > /tmp/webmcp-poc/search-tool.html << 'EOF'
  <form
    toolname="searchProducts"
    tooldescription="Search the product catalog by keyword and category"
    toolautosubmit="true"
    action="/api/products/search"
    method="GET"
  >
    <input name="q" type="search" tooldescription="Search keyword or product name">
    <select name="category" tooldescription="Product category filter">...</select>
  </form>
  <script>
    if ('modelContext' in navigator) {
      navigator.modelContext.registerTool({ name: 'getProductDetail', ... });
    }
  </script>
EOF

# Parse and audit WebMCP structure
python3 webmcp_audit.py

Output (local validation)

=== WebMCP Declarative Tools Found ===
  Tool: searchProducts
  Description: Search the product catalog by keyword and category
  Auto-submit: true
  Endpoint: GET /api/products/search
  Parameters (2):
    - q (input): Search keyword or product name
    - category (select): Product category filter

Total declarative tools discovered: 1
Imperative tool registration (navigator.modelContext.registerTool) present: YES
Chrome 145+ required for live agent interaction

PASS: WebMCP HTML structure is valid and parseable

Sources Verified

1. developer.chrome.com/docs/ai/webmcp — Official WebMCP spec page. Confirms Declarative API (HTML form attrs: toolname, tooldescription, toolautosubmit) and Imperative API (navigator.modelContext.registerTool()).
2. developer.chrome.com/docs/ai/webmcp/declarative-api — Attribute surface confirmed: toolname (tool identifier), tooldescription (natural language description), toolautosubmit (boolean, skip confirmation).
3. developer.chrome.com/blog/webmcp-epp — Early preview launched February 10, 2026 for Chrome 145+. Chrome 149 extended origin trial announced at Google I/O 2026 (May 19-20).
4. webmcp.link — W3C Web Machine Learning community group incubation confirmed. Microsoft co-developing.
5. developer.chrome.com/blog/chrome-at-io26 — Google I/O 2026 announcement confirmed: Gemini in Chrome will support WebMCP APIs.
6. dev.to/czmilo/chrome-webmcp-the-complete-2026-guide — Comprehensive technical guide confirming navigator.modelContext API surface and both API types.

Limitations

• navigator.modelContext API is not available outside Chrome 145+ with the WebMCP flag or Chrome 149 origin trial
• Live agent interaction test not performed (requires enrolled origin trial token)
• Standard DOM scraping fallback behavior not tested (only the WebMCP path demonstrated)
• Gemini in Chrome (the primary WebMCP consumer) is not yet GA — origin trial status

Evidence Level

Local HTML validation confirms declarative annotation structure is correct. API surface confirmed from official Chrome for Developers documentation. Origin trial status and Chrome version confirmed from two independent sources.