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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world scope, so the safety profile is covered. The description adds genuine behavioral context beyond that: the result is a single ranked action bundled with a reason, a drafted message, and a deep link, which tells the agent this is a composed, opinionated read rather than a raw query.

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 sentences with no filler, and the usage trigger is front-loaded ahead of the return-value summary. The second sentence is slightly redundant with the output schema but still reads efficiently.

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?

With an output schema present, the description need not enumerate return fields, and it still summarizes the payload shape (action + reason + drafted message + deep link). Combined with annotations covering the safety profile and zero parameters, the definition is complete enough to invoke correctly; only the sibling routing to agent.actions.list is unstated.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline for a parameterless tool is 4. No parameter-level meaning is missing.

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 resource (the single highest-leverage relationship action) with a clear verb implied by 'returns', and the 'single most important' framing implicitly distinguishes it from the list sibling agent.actions.list. It stops short of naming that sibling, so differentiation is inferred rather than explicit.

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 gives a clear trigger ('When the user asks what they should do next about their relationships') which is genuine usage guidance. However it never names the obvious alternative agent.actions.list or states when this tool is the wrong choice, leaving the relationship between 'next' and 'list' to inference.

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