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

Beyond the annotations, the description discloses the asynchronous behavior: it returns an audit_id immediately, the run takes 2–5 minutes, and get_measurement reads it later. It also explains caching behavior (a previous measurement returns its full result at once) and that results are published as a report page on webspeed.pro, which is valuable context for an open-world, non-destructive measurement tool.

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?

The description is dense but well organized: action and return value first, then timing, retrieval via get_measurement, caching behavior, report publishing, and finally when to use it. Every sentence contributes useful information without repetition.

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 single-parameter tool with no output schema, the description covers what the tool does, what it returns immediately, how long the run takes, how to retrieve the result, caching behavior, and where the report is published. An agent has enough context to call it and route follow-up reads to get_measurement.

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?

There is only one parameter and the schema description coverage is 100%, so the schema already explains that url accepts addresses like example.com or https://example.com/pricing. The description adds context about what is measured but no additional parameter syntax or constraints beyond the schema.

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?

The description states a specific verb and resource: it starts a real PageSpeed Insights measurement of a web page, comparing the original site against a WebSpeed Fast-accelerated copy on mobile and desktop. It clearly distinguishes the action from the sibling get_measurement, which reads the result.

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?

It gives explicit use cases ('why a site is slow, how fast it is, or what can be sped up') and explains that get_measurement retrieves the eventual result. It does not explicitly state when not to call measure_site, such as when an existing measurement should simply be read, but the sibling relationship is clear.

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