webmcp_call

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already flag destructiveHint=true and openWorldHint=true, but the description adds the crucial gate: which tool classes (buy, pay, send, delete, POST form) are held back without confirm:true, and the exact remediation loop. It also enumerates the return surface (status values, result, ms, navigated_to), which no output schema provides.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three dense sentences, front-loaded with purpose then returns then safety flow; no filler. It is tight but slightly overloaded — the status enumeration and the confirmation protocol compete for attention in one breath, where a short split would read faster.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, yet the description names every meaningful return field including all six status values and navigated_to, so an agent knows what to branch on. Combined with the confirm protocol and tab targeting hints, nothing needed to invoke it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so baseline is 3; the description earns above that by tying `confirm` to a user-approval precondition and explaining the needs_confirmation round-trip rather than just the boolean. It doesn't elaborate on `input` (arguments must match the target tool's input_schema) or on frame_id beyond what the schema states.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Run a WebMCP tool the page declares') and immediately identifies where the tool list comes from (webmcp_tools or the webmcp line of navigate). It distinguishes itself from click/type_text/fill_form by framing the tool as 'one call instead of the clicks and fields it replaces.'

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit routing to webmcp_tools/navigate for discovery, an explicit alternative comparison (one call vs. the click-and-fill sequence), and a concrete escalation path for sensitive tools: needs_confirmation → ask the user → repeat with confirm. Nothing about when to use it is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.