Origin vs specific page

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds meaningful behavioral details beyond those: it makes 2 API requests, returns p75 + rating per metric, and discloses that either side can return no_data. This gives the agent practical expectations without contradicting the 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 concise at three sentences, with each sentence delivering useful information (purpose, API-request count, no_data behavior, default metrics, required params). It is front-loaded with the core comparison purpose. The only slight issue is the potentially misleading 'default metrics' phrase, but structurally it is tight.

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?

There is no output schema, so the description carries the burden of explaining return value semantics. It does state 'p75 + rating per metric' and covers the no_data edge cases, which is good. However, it omits details about how metrics and form_factor interact, and the contradictory default-metrics comment creates ambiguity. For a moderately complex comparison tool, this is adequate but not fully complete.

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%, so baseline is 3. The description adds emphasis that both origin and url are required (unlike other tools), which is helpful. However, it also states 'Default metrics: the three Core Web Vitals,' which directly contradicts the schema's instruction that omitting metrics returns all available metrics. This inconsistency confuses the parameter semantics and reduces the score.

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 ('compares') and clearly identifies the two resources ('site-wide origin record' vs 'one specific page'). It also distinguishes from sibling tools by noting that both origin and url are required here, unlike the other tools. This makes the tool's unique purpose immediately evident.

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 context by explaining the comparison goal ('tell whether a page is faster or slower than the site average') and useful caveats around no_data. However, it does not explicitly name alternative tools or state when not to use this tool, though the 'unlike the other tools' hint partially addresses this. This is strong but not fully explicit.

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