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

Annotations already declare the write/safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds no behavioral context beyond them: it does not warn that retries create duplicate links (non-idempotent), nor explain that approval_id represents a human-approved, single-use authorization despite that being a notable operational requirement.

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?

Two short sentences with the trigger front-loaded and no filler. The second sentence ('Links the two contacts with the relationship') is slightly redundant with the first but still earns its place as the action statement.

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?

An output schema exists, so return values need not be explained, and annotations carry the safety profile. For a low-complexity, four-parameter create call, the description covers trigger and action adequately; only the duplicate/idempotency caveat 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%, so all four parameters are documented in the schema itself, including the 'From list_relationship_types' note for relationship_type_id. The description's example only restates the contact_is/of_contact mapping already given by the schema, adding no new semantic detail.

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?

States a specific verb and resource: links two contacts with a relationship, plus a concrete example ('Sarah is James's sister'). An agent can tell this creates a relationship, but the description never differentiates it from siblings like relationships.list or relationships.delete, nor from contacts.merge which also links people.

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 opening clause gives a usable trigger ('when the user tells you how two people are related'), which is genuine usage context. However, it names no alternatives, no preconditions (e.g. checking relationships.list first to avoid duplicates), and no when-not-to-use guidance.

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