Install any skill in seconds. Free to start, no credit card required.
Get Started Free →qdhenry/webmcp
Implement WebMCP in web projects — add browser-native structured tools for AI agents using imperative JS or declarative HTML APIs. Full lifecycle from setup through testing and optimization.
Passed 20 of 23 test cases with the skill, and 12 of 23 without it.
and 5 more in the full report
8 fixed12 passed either way3 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 8 test cases the skill fixed. Same model, same prompt, with and without the skill.
When converting an existing HTML `<form>` for client-side agent tool discovery, what exact HTML attribute name is placed on the form element to define the tool's description?
| Checked | Without skill | With skill |
|---|---|---|
| Identifies tooldescription as the HTML attribute name for tool descriptions. | Missed | Passed |
The instructions your model reads when the skill loads.
<essential_principles>
WebMCP is a browser-native standard that exposes structured tools for AI agents on websites. Instead of screen-scraping, agents interact through typed JavaScript APIs and HTML annotations.
Two APIs:
window.navigator.modelContext — register tools via JavaScripttoolname/tooldescription attributes on <form> elementsPrerequisites: Chrome 146.0.7672.0+, chrome://flags/#enable-webmcp-testing enabled.
Core principles that always apply:
Tools must be atomic and composable — one function per tool, no overlapping tools with nuanced differences. Combine similar tools into one with input parameters.
Accept raw user input — tools should accept natural strings (e.g., "11:00") not computed values (e.g., minutes-from-midnight). Minimize cognitive computing for the model.
Validate in code, not schema — schema constraints are helpful but not guaranteed. Validate within execute functions and return descriptive errors so agents can self-correct.
Update UI before returning — agents use UI state to verify execution. Ensure execute/submit logic updates visible state before resolving.
Positive, verb-first descriptions — describe what the tool does and when to use it. Avoid negations. "Creates a calendar event for a specific date" not "Do not use for weather."
</essential_principles>
Wait for response before proceeding.
test cases passed, vs 12 / 23 without
More skills from the same source and nearby in the registry, with their headline benchmark lift.