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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, covering the safety profile. The description adds valuable context beyond annotations: it specifies the exact return fields (activity type, value, units, pChEMBL, etc.), explains the comparability of pChEMBL, and states the data source and licensing. This goes beyond what annotations provide and helps the agent set expectations.

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 paragraph that front-loads the main action and then systematically covers return fields, filtering, requirements, data scale, and licensing. It is longer than two sentences but every sentence contributes meaningful information without redundancy. The structure is logical and avoids verbosity.

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 input schema descriptions, the description is quite complete. It covers the query requirements, optional filtering, and the nature of returned data, plus source/licensing. It does not mention pagination or default ordering, but these are minor gaps given the output schema exists and annotations already indicate open-world and read-only behavior.

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 descriptions cover 100% of parameters with detailed explanations, including common activity_type values and examples for molecule and target IDs. The description reinforces the requirement for at least one of the two IDs, which is already in the schema, and adds an example for activity_type. This adds marginal value beyond the schema, so the baseline of 3 is appropriate.

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 clearly states the verb 'retrieve' and the resource 'bioactivity data for a drug molecule or biological target' from ChEMBL. It enumerates the returned fields, making the purpose unambiguous. It does not explicitly name sibling tools like chembl.molecules.detail, but the description's focus on potency measurements distinguishes it well enough from other ChEMBL tools.

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 gives clear context on how to query (requires at least one of molecule_chembl_id or target_chembl_id, optional activity_type filter) but does not explicitly state when to use this tool over alternatives such as chembl.molecules.search or chembl.targets.search. The guidance on filtering by activity_type is useful, but exclusions and alternatives are not mentioned.

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