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

With annotations covering the safety profile (destructiveHint=true, idempotentHint=false), the description adds genuinely useful behavioral context: it is a partial/merge update where omitted fields keep their current value, and it returns updated trunk attributes or a readable error. It does not, however, flag which specific changes are destructive or require elevated permissions, so it stops short of a 5.

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 tightly written sentences: identity/scope first, calling convention second, sibling routing third, return behavior last. Zero filler and each sentence carries distinct information.

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 12-parameter mutation tool with no output schema, it covers the essentials: what it mutates, partial-update semantics, sibling routing, and the return shape. Annotations carry the safety profile, so nothing an agent needs to call it 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 description coverage is 100%, so the baseline is 3, but the description earns extra credit by explaining the merge semantics that govern every parameter — only supplied fields change, omitted fields are preserved. That is real meaning beyond the per-field schema text, though it does not explain the null-vs-omit distinction in its own words.

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 (Update), a precise resource (phone.systems Voice IN Trunks), and scopes it to the authenticated customer. It explicitly differentiates itself from update_sip_trunk and update_pstn_trunk, so an agent can distinguish it from the nearest siblings without opening a 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?

Gives explicit routing rules: SIP trunks go to update_sip_trunk, PSTN trunks to update_pstn_trunk, and this tool is for phone.systems Voice IN trunks. It also states the calling convention (pass id, pass only fields to change), leaving nothing to inference.

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