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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, so the safety profile is covered. The description still adds real behavioral context not present in structured data: the operation consumes no credit (cost) and returns a reconciliation of checkable vs. uncheckable findings, which tells the agent what state the site's memory is in.

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?

Two sentences, front-loaded with the action and its scope before the usage cue. The middle clause listing returned content is slightly baggy but each element (observed / came back / not checked) carries distinct meaning, so there is little waste.

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 covers what it is, when to call it, cost implications, and the rough shape of what comes back. That is close to complete; only auth or error behavior is left unstated, which is minor here.

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 a single url parameter at 100% schema description coverage, and the schema already gives format examples (https://yoursite.com or yoursite.com). The description adds nothing about the parameter, so the baseline of 3 applies when the schema does all the work.

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?

Names a specific verb ("Reads") and resource ("the UX memory of a site") and enumerates the scope of the content: last measurement, what came back, what could not be checked. It also explicitly separates itself from the measurement sibling by stating "It does not measure," so an agent can distinguish it from medir without opening a 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?

"Call it before you start changing what users see on that site" is an explicit usage trigger, and "It does not measure and uses no credit" implicitly routes measurement work to medir. It stops short of naming the alternative tool or any other alternatives, so it is clear context rather than full when/when-not guidance.

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