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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint as false. The description adds useful context about matching and existing-subject reuse, but does not disclose no-match behavior, result shape, or pagination. No contradiction with annotations is present.

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 front-loaded with the main action and is fairly tight. Some redundancy exists between the first and third sentences, both emphasizing lookup before creation, but each sentence adds matching or reuse context.

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?

The description provides enough orientation to select the tool and understand why it should be called. Since there is no output schema, more detail about what the returned subjects look like or how absence of a match is handled would improve completeness.

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 description coverage is 0%, so the description carries the parameter-documentation burden. It gives semantic meaning for canonical_key, name, subject_type, and identifier_value, but it does not explain limit, identifier_key, or the anyOf constraint saying that at least one selector must be supplied.

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 identifies the tool as a lookup operation for an existing subject and lists several match types: canonical key, name, and identifier. It also frames the purpose as pre-creation deduplication. It does not explicitly differentiate from similar siblings like resolve_subject_type or resolve_subject_hierarchy, but the resource and action are clear.

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 explicit timing guidance: use this before adding or declaring a new subject so the existing subject_id and canonical_key can be reused. It does not spell out when an alternative sibling should be used instead, but the recommended workflow is clear.

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