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

Annotations already declare a read-only, open-world call, and the description adds real substance beyond them: the 28-day CrUX window, the exact metrics measured, and the absence of lab testing. The return shape is also sketched (ranking plus a link), though limits such as data-unavailable domains are not 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?

Three short sentences, front-loaded with the core action and data source, then usage, then a scoping exclusion. Nothing is redundant or padded.

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?

With no output schema, the description usefully states that a ranking and report link are returned, and it pins down the data source and time window. It stops short of covering edge cases like sites with insufficient CrUX data, but is otherwise sufficient for correct invocation.

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% and every parameter is already documented in the schema, including the 2-5 URL cardinality and the category/language semantics. The description adds no syntax or format detail beyond what the schema provides, so baseline 3 applies.

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 gives a specific verb ('compares'), a concrete resource ('Iron/Out UX Score of 2 to 5 websites'), and names the underlying data source (CrUX, last 28 days, Web Vitals metrics). An agent can distinguish this from a generic benchmark tool without opening the schema.

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 states the intended scenario ('competitor or sector comparisons') and a clear exclusion ('runs no lab test or Lighthouse'), which is valuable negative guidance. It does not, however, name the sibling run_ux_benchmark or say when to prefer it, leaving the alternative implicit.

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