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

Annotations already signal a mutating, non-idempotent operation, and the description adds a useful precondition that the relationship must already exist. It does not disclose duplicate handling or whether an existing URL is replaced, but the basic side effect is clear.

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?

One tightly worded sentence communicates the action, the target resource, and the required predecessor call. Every phrase 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 simple two-parameter, no-nested-objects mutation with an output schema and adequate annotations, the description covers what the tool does and the key input provenance. Nothing an agent needs to invoke it correctly is missing.

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 100%, with both url and subjectRelationshipId already explained in the schema. The description only repeats the provenance of subjectRelationshipId and adds no meaning beyond the schema, so baseline 3 applies.

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 uses a specific verb ('attaches') and resource ('a url to an SMI subject relationship'), and clarifies it operates on an existing relationship via subjectRelationshipId. This makes it distinct from sibling tools like smi_add_subject_url, which attaches URLs to a subject rather than a relationship.

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?

It states when the tool is appropriate: after smi_add_subject_relationship has returned the relationship ID. It does not explicitly enumerate alternatives or exclusions, but the precondition is clear and the sibling set makes the routing obvious.

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