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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and reach profile is covered. The description's field list largely duplicates what the output schema already exposes, and it adds no behavioral detail such as pagination limits on the 'recent articles' portion or rate/auth constraints. Consistent with calibration, a 3 is appropriate when annotations carry the safety story and the description adds only marginal context.

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 what is returned and followed immediately by sibling routing. No filler, no restatement of the tool name.

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 an output schema present the description need not explain return values, and annotations cover safety, so the essential information is in place. The one omission is that neither param is required and either url or slug suffices, which is left entirely to the schema.

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 the schema itself explains that url (canonical mirror.co.uk/authors/<slug>/ URL) is an alternative to slug. The description adds no parameter guidance beyond that, so the baseline 3 applies when the schema does the heavy lifting.

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?

States a specific verb (Fetch) plus resource (one Mirror author's public profile) and enumerates exactly what comes back: name, job title, bio, email, X/Twitter handle, recent articles. It also names the sibling tools it is not, so an agent can distinguish it from mirror_article, mirror_headlines and mirror_news 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?

Explicitly routes the agent: use mirror_article for a single story's content, and mirror_headlines/mirror_news for current outlet feeds. Both the when-to-use and the alternatives are stated, leaving nothing to inference.

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