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

Annotations already declare destructive=true and idempotent=false, so the safety profile is covered; the description adds real value beyond that by stating the update is partial, that trunk type is immutable, and that passwords are never returned. It still doesn't discuss reversibility or permission requirements, keeping it at a 4.

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?

Dense but front-loaded: the update operation and its partial semantics come first, followed by type-specific behavior and placeholders. Every sentence carries information, though the single long paragraph is slightly heavy.

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 14-parameter mutation tool, the description covers the distinguishing constraints (partial update, immutable type, password non-disclosure, placeholder semantics) and even states the return shape, so nothing essential is missing despite the absence of an output schema.

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 meaning the schema lacks: the full list of {SMS_*} placeholders and where they can be substituted (SMTP subject/message, HTTP IN query_parameters/headers/body), plus the HTTP-IN vs SMTP field split.

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 (update an SMS trunk by id) and names the sibling that produces the id (list_sms_trunks), so an agent can distinguish it from create_sms_trunk and update_sms_trunk_group immediately.

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?

Clearly frames this as a partial update with the same field semantics as create_sms_trunk, and warns that the trunk type cannot be changed. It does not explicitly state when to prefer this over sibling update tools or prerequisite permissions, so it falls just short of a 5.

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