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

Annotations already cover readOnly/idempotent/non-destructive safety, so the description doesn't need to restate that. It adds meaningful behavioral constraints: only open-access articles, response capped at ~40k chars, PMID→PMC resolution, and the has_full_text:false fallback. These go beyond the annotations without contradicting them.

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 sentences, with purpose front-loaded, followed by usage guidance and behavioral caveats. The example phrasings are useful without being verbose. Every sentence earns 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?

For a single-parameter tool with no output schema, the description covers input formats, resolution behavior, return scope, truncation cap, and the no-full-text fallback. An agent has enough information to select and invoke the tool correctly.

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?

The schema already documents the single pmid parameter with 100% coverage, including both PMID and PMC id examples, so the baseline is 3. The description adds modest value by explaining the resolution step ('Resolves the PMID to its PMC id'), which clarifies why PMC ids are accepted and how the lookup works.

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: 'Fetch the FULL TEXT of a biomedical paper from PubMed Central (the open-access subset) by PubMed ID.' It also clearly differentiates from the closest sibling get_abstract by emphasizing full body text. The scope and behavior are unambiguous.

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?

Gives an explicit preference directive: 'PREFER OVER get_abstract when you need methods/results/discussion, not just the abstract' with concrete example phrasings. It also provides the fallback condition: returns has_full_text:false, so use get_abstract otherwise. This fully routes an agent to the right tool.

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