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

Annotations already declare readOnlyHint=false and idempotentHint=false, so the agent knows this is a mutation. The description adds a behavioral detail—that the relationshipId is sourced from smi_list_relationships—which is useful. It doesn't mention side effects (e.g., non-idempotency) or prerequisites like subject existence, but given the annotations cover the safety profile, a 3 is reasonable.

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 immediately specifies the source of the relationshipId. There is zero redundancy or filler, making it highly concise.

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 tool has 5 parameters (4 required) and an output schema, so the schema covers parameter details and return values. The description provides the core purpose and the prerequisite for relationshipId. It doesn't mention error conditions or additional behavior, but for a simple relationship-attachment tool with annotations covering mutation, this is sufficient.

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%, so all parameters are already documented. The description adds a small semantic clarification for relationshipId (its source from smi_list_relationships), which goes beyond the schema. However, it doesn't add anything for the other parameters, so the baseline of 3 stands with a slight bonus.

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 states a specific verb ('Attaches') and resource ('relationship to an SMI subject'), making it clear what the tool does. It also references the source of the relationshipId, which distinguishes it from other add-subject tools. It doesn't explicitly list all sibling differentiations, but the name and description are sufficiently 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 provides a key usage hint: the relationshipId must come from smi_list_relationships, implying a prerequisite step. It doesn't explicitly state when not to use this tool (e.g., for addresses or emails), but the tool name and sibling list make that obvious. It gives context without exclusions, so a 4 is appropriate.

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