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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: DOI/PMID are only present 'when the site has them' (conditional fields), the site is a fixed small corpus of 93 references, and citing topics are included in the response.

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, both front-loaded: what you get first, then where the key comes from. No filler, and the corpus size is stated in a compact clause rather than a separate sentence.

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, and the description compensates by naming the returned fields and their conditional nature. For a one-parameter lookup with annotations covering the safety profile, nothing an agent needs in order to call it correctly is missing.

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% and already describes the key field, so the baseline is 3. The description earns an extra point by supplying example key formats and specifying the two sibling tools that produce valid keys, which the schema does not.

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 and resource ('Full citation for one reference key') and enumerates the returned fields: DOI, PMID, site link, and citing topics. The example keys (shalev2000, grosstsur1996) make the shape of the input concrete, so an agent can distinguish it from list-oriented siblings immediately.

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 tells the agent where keys come from ('keys are returned by get_prevalence and list_studies'), which is real routing guidance for obtaining the required parameter. However, it never addresses the closest-sounding sibling get_citation or states when-not to use this tool, leaving a differentiation gap.

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