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

Annotations already establish readOnly, idempotent, non-destructive and closed-world, and the description still adds substantial context beyond them: the results-null-until-complete lifecycle state, the results_unavailable fallback when stored results cannot be read, and a note that the unread data lives in the Yellowhead app. It even flags an interpretive caveat — citations vary between runs and are not on their own evidence of why a site was or was not cited — which no annotation could convey.

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 purpose is correctly front-loaded in the opening clause, but the remainder is one long chain of clauses enumerating return fields, which is hard to parse and would be better as a short list. The 'in the Yellowhead app' disclaimer about cited page addresses is repeated in spirit at the end after already being covered by the results_unavailable sentence, so some wording does not earn its place.

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 carries the full burden of describing return values, and it does so thoroughly — including the null/unavailable edge states and the head-to-head competitor questions. What is missing for a single-parameter lookup of this complexity is only the provenance of the id and any note on result size or auth, which are minor relative to what is covered.

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 required parameter whose schema has zero description coverage, so the description must carry the meaning. It says 'by id' and consistently frames the scan as an identified object, but it never states the id is a UUID or where the caller obtains one, which leaves a real gap for a 0%-coverage schema. It beats a bare baseline because the surrounding text makes the identity relationship unambiguous, but it does not fully compensate.

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 first clause names a specific verb and resource with scope: 'Returns one Citation Scan by id,' which immediately separates it from the list_citation_scans sibling. The rest of the description enumerates exactly what the returned object contains (website, category, country, status, dates, competitor_domains, results, head-to-head questions), so an agent knows what it is fetching before opening any 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?

Usage is only implied: the tool fetches a single scan by id, so an agent infers it should call list_citation_scans first to obtain an id, but the description never says this or names that alternative. There is one useful conditional hint — 'results is null until the scan completes' implies you should not call it expecting results on a running scan — but there are no explicit when-to-use or when-not rules.

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