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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true, covering safety and idempotency. The description adds context about the returned data fields but does not disclose error behavior (e.g., invalid ligand ID) or authentication requirements.

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 description is a single, well-structured sentence that front-loads the purpose and lists key output fields. Every word is necessary and efficient, with no redundancy.

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?

Given the presence of an output schema and comprehensive annotations, the description covers the main functionality and output fields adequately. It does not address behavior on missing IDs or rate limits, but for a simple lookup tool, this is acceptable. The openWorldHint suggests it may work with future entities.

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 input schema already provides detailed description of the ligand_id parameter with examples. The tool description adds value by mentioning the broader scope ('covers ATP, HEM, NAG, drug molecules, cofactors, ions, and 40K+ chemical entities'), which enhances understanding beyond the schema's examples.

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 description specifies the verb 'Get' and the resource 'chemical component data for a ligand/small molecule by its 3-letter PDB code', listing specific output fields. It distinguishes itself from sibling PDB tools (science.pdb.search, science.pdb.sequence, science.pdb.structure) by focusing exclusively on ligand chemistry.

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?

The description implies usage when ligand chemical data is needed, but it does not explicitly state when to use this tool versus alternative PDB tools (e.g., for other PDB queries) or provide exclusion criteria. No 'when not to use' guidance is given.

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