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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds genuine context the annotations cannot: contacts are stored only on request, retained one year after the last save, come with a version token for safe updates, and are not proof of address deliverability. It stops short of rate limits or auth requirements.

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?

Four short sentences that are front-loaded with the purpose and read-only guarantee. The retention/disclaimer sentence is extra but carries real caveat value; nothing is padded or circular.

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, return values need not be detailed, and annotations handle the safety profile, so the remaining burden is parameter and paging behavior — which is the one real gap. Purpose, retention caveat and version-token note make it otherwise sufficient for a low-risk lookup tool.

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% and all four parameters (key, limit, query, offset) are undocumented in the schema, so the description must compensate. It only alludes to "a label or key", leaving the pagination contract (limit max 25, offset max 10000, default paging) and the free-text query parameter with no meaning added anywhere.

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 ("Returns") and resource (private saved recipients and return-address contacts) plus the matching criterion (label or key). The read-only framing cleanly separates it from the write-oriented siblings postedly_save_contact and postedly_delete_contact, so an agent can route correctly without opening the schema.

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?

Usage is only implied: the agent can infer this is the lookup tool for saved contacts, but no explicit when-to-use condition, prerequisite, or alternative (e.g., listing vs. saving vs. deleting) is named. It never tells the agent when NOT to call it or what to call instead.

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