Measure the rendered page

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

With no annotations, the description carries the full burden; it does disclose that every rule returns its definition and threshold, which is genuinely useful output context. However, it never states that this is a non-mutating read, whether it navigates or waits, or how long a run takes, leaving the mutation/safety profile to inference.

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?

Two dense sentences with the rule inventory front-loaded, and no filler. The closing claim about rule definitions and thresholds is slightly terse but still earns its place by describing output shape.

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?

For a one-parameter, no-output-schema tool, the description mostly suffices: it substitutes for an output schema by describing that results are per-rule with definitions and thresholds. It is still incomplete on the stage_id contract and on the precondition of an open, loaded stage.

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?

The single parameter stage_id has 0% schema description coverage, and the description never mentions it at all — not what a stage is, how to obtain an id, or what happens if it refers to a closed stage. The description therefore fails to compensate for the documentation gap.

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 ('run rule-based measurements') on a specific resource ('the live page') and enumerates the exact rule categories covered: overflow, broken images, missing alt, tap targets, clipped text, plus console/page/network errors. This is clearly distinguishable from siblings like capture (visual snapshot) or diff (comparison).

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?

No guidance on when to use this versus capture, diff, or act, and no exclusions or prerequisites stated beyond the implicit hint that a live page must exist. The agent must infer that a stage must be open and the page loaded before measuring.

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