rcsb_get_polymer_entity_instances

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

Annotations already indicate read-only and idempotent behavior. The description adds valuable behavioral context beyond annotations: default fields returned, unknown IDs placed under 'not_found', and the ability to override defaults with a custom GraphQL field selection. It does not contradict the annotations.

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 well-structured with a brief summary, default fields line, and a concise Args list. It avoids redundancy and each sentence provides useful information without unnecessary padding.

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 tool's simplicity, the description covers all essential aspects: purpose, ID format, default fields, error handling for unknown IDs, and how to customize fields. With an output schema present, the description need not explain return values, so it is fully complete for effective tool invocation.

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 0%, so the description must justify parameter meanings. It thoroughly explains instance_ids with format (entry.asym_id) and example, plus error handling for unknown IDs. It also explains the fields parameter as an optional GraphQL selection, replacing the curated default, and points to rcsb_describe_data_object for discovery.

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 it fetches polymer entity instances (individual chains), with an explicit example of the instance ID format. This distinguishes it from sibling tools like rcsb_get_polymer_entities (which returns entities, not chain-level instances) and other instance-specific 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 implies usage through 'Fetch polymer entity instances (individual chains)' and provides parameter details, but it does not explicitly mention when to use this tool over alternatives or when not to use it. No sibling tool is referenced, so the guidance is only implicit.

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