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

Beyond annotations (readOnly, idempotent, non-destructive), the description adds that the tool does not execute JavaScript or bypass access controls, and explains cache reuse behavior. No contradictions with annotations.

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 two sentences, each providing essential information: purpose and usage guidelines. Front-loaded with key action, no redundant words.

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?

Given the simple tool function (timing), high schema coverage, and annotations, the description fully covers what an agent needs: constraints, cache behavior, and parameter usage. An output schema exists, so return values need no explanation.

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% with detailed descriptions for both url and fresh parameters. The tool description reiterates similar points without adding new meaning, so baseline 3 is appropriate.

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 clearly states the tool returns measured end-to-end fetch timing, specifies it is for public HTTP(S) resources only, and distinguishes it from siblings by focusing on timing. The title 'Url Timing' and name 'web.url.timing' align perfectly.

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?

The description provides clear guidance: use only for public HTTP(S) resources, do not use if JavaScript execution or access control bypass is needed, and advises on fresh parameter usage. It lacks explicit mention of alternative sibling tools but gives sufficient context for correct selection.

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