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

Annotations already declare readOnlyHint=true, but the description adds real behavior: default ordering ('Newest first'), the destructive-to-filters effect of is_new, the returned fields, and the underlying endpoint. It stops short of describing pagination behavior (total counts, next page), which is the remaining gap.

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?

Three short sentences with zero filler; the identity of the resource comes first, then the returned fields, then the ordering, then the one behavioral caveat. Every sentence carries information an agent can act on.

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 14 parameters and no output schema, the description wisely enumerates the returned fields and flags the one surprising filter interaction. Only pagination/result-envelope behavior is unaddressed, which is a minor omission for an otherwise self-sufficient definition.

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 14 parameters are already documented, and the enum values for sort_order and date_preset live in the schema. The description reinforces only the is_new override and the default ordering, adding marginal meaning beyond structured data, 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?

States a specific verb and resource ('List voicemail messages') and then disambiguates the resource by defining it as 'call records with status VOICEMAIL', which cleanly separates it from the sibling rinkel_list_calls. It also names the fields returned, so an agent knows exactly what shape of thing it is getting.

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?

There is one explicit usage rule ('With is_new=true Rinkel ignores every other filter and returns only unplayed voicemails'), which is genuinely useful. However, it never says when to prefer this over rinkel_list_calls or rinkel_count_new_voicemails, so the choice among siblings is left to inference.

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