check_performance

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

Annotations already declare readOnlyHint=true, so the agent knows this is non-destructive. The description adds value by specifying the exact output metrics returned, which is especially helpful given there is no output schema. It does not mention potential timeouts or network dependency, but the read-only behavior is adequately covered.

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 a single, front-loaded sentence that states the core action first and then lists the return metrics efficiently. Every phrase earns its place with no redundant or filler content.

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, read-only tool with no output schema, the description is complete: it identifies the URL input, explains what the tool measures, and enumerates the returned timing values. The annotations cover side-effect safety, so no further behavioral disclaimers are essential.

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 coverage is 100%, with the url parameter already described as 'URL to analyze.' The description reinforces that the URL is a website to measure performance for, but does not add meaningful new parameter-level detail 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 uses a specific verb, 'Measure website performance,' and enumerates concrete metrics (DNS lookup, TCP connect, SSL handshake, TTFB, content download, total load time). This clearly distinguishes it from sibling tools like check_ssl or check_headers, which focus on different aspects of a website.

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 no guidance on when to choose this tool over alternatives, nor does it mention exclusions or prerequisites. While the purpose is clear, there is no explicit routing to sibling tools such as trace_redirects or check_headers.

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