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

Beyond the readOnly/idempotent annotations, it discloses the permission scope (lines:manage), that it 'changes nothing', per-account rate limiting, the recency ceiling, and the absence of audio links or transcripts with a URL to get them. It also describes pagination mechanics (next_before null signals no older page).

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?

Front-loaded with purpose and the differentiating detail, then pagination, then exclusions. It is dense and multi-clause with several semicolon-chained ideas in the final sentences, which costs a little readability, but essentially every sentence carries information an agent needs.

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 no output schema, the description compensates by enumerating every returned field (id, at, caller, duration_seconds, summary, urgent, next_before). Combined with paging, auth, and scope limits, nothing an agent needs to call this correctly 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 coverage is 100%, so baseline is 3, but the description adds real meaning: line_id's provenance, that limit is a page size, and that before should be fed the previous result's next_before rather than an arbitrary timestamp. It stops short of restating the 1-100 range or the 40-char cursor limit, which the schema already carries.

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 the incoming calls answered by one of the signed-in owner's own lines'), plus ordering ('newest first') and the key differentiator from get_answering_line (full E.164 caller number vs last four digits). An agent can distinguish it from get_line_messages and get_call_result by the explicit routing sentences.

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?

Names the prerequisite source for line_id (get_answering_line) and explicitly routes three sibling cases: voicemail content to get_line_messages, outbound calls to get_call_result, audio/transcripts to the owner console. It also states a when-not condition ('covers recent calls only, so older ones may not be returned').

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