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

With no annotations, the description carries the transparency burden. It discloses output content (inbound/outbound, duration, direction, voicemail transcripts) and honestly notes transcripts are only included 'where available'. It does not explicitly state read-only behavior, but 'List' strongly implies a non-mutating 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?

Three sentences with no filler: purpose and output fields first, then parameter guidance, then concrete example queries. Every sentence earns its place and the most decision-relevant information is front-loaded.

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?

For a simple filtered-list tool with three fully documented parameters and no output schema, the description covers what the tool returns, how to filter, and real user questions it answers. An agent has enough context to select and invoke it correctly.

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 the baseline is 3, but the description adds real meaning to contactId and voicemailOnly by tying them to user intents ('see calls with one person', 'see just calls that left a voicemail'). The limit parameter is not re-explained, but the schema already fully documents it.

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 uses a specific verb ('List') and resource ('the user's call history'), then names key result fields and filter options. It is clearly distinguishable from the sibling calls_get, which implies single-record retrieval, without needing to open 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?

The description gives concrete use cases ('who did I speak to this week?', 'did anyone leave a message?') and explains when to use contactId and voicemailOnly. It does not explicitly mention alternatives or when not to use this tool, so it stops short of a full 5.

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