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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds value by disclosing what the list returns (direction, duration, voicemail transcripts) and that single-call mode includes recording details, but it says nothing about pagination or how the default/vs max limit behaves.

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?

A single well-formed sentence with the primary list purpose front-loaded and the alternate `id` mode appended. No wasted words.

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 partially compensates by naming returned fields, but leaves out pagination/limit behavior and the undescribed `contactId` parameter. Adequate for a simple read tool, but not fully complete.

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 75%, so the schema carries most parameter documentation; `limit`, `voicemailOnly`, and `id` are described there. The description only implicitly maps to `id` and doesn't mention `contactId` (undocumented in the schema) or limit semantics, so baseline 3 is appropriate.

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 verb+resource ('List call history') and enumerates the fields returned, then names the alternate single-fetch mode via `id`. It clearly separates list vs. single-call behavior, though it does not explicitly contrast itself with neighboring list tools like sms_list.

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 explicit routing guidance: use the default list mode, or pass `id` to fetch a single call with recording details. There is no statement of when not to use it or of alternative tools, but the mode selection is unambiguous.

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