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

Annotations already declare it is a non-readOnly, non-destructive, non-idempotent mutation. The description adds context beyond that: registration credentials are generated server-side and returned masked, omitted fields keep panel defaults, and an invalid configuration yields a readable error. It does not mention auth scopes or rate limits, keeping it just 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?

Front-loaded with the core purpose, then scope guidance, the registration variant, sibling alternatives, and return behavior. Four sentences, each doing work, though the sibling-routing and registration details make it slightly dense for a single paragraph.

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 48-parameter creation tool with no output schema, the description covers the essential edges: minimal viable call, registration-mode constraint, defaults behavior, sibling alternatives, and return/error format. The schema handles the exhaustive parameter detail, so the description is appropriately complete without being redundant.

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% across all 48 parameters, so the schema already carries full parameter semantics. The description reinforces a few key meanings (host as R-URI host, minimal required fields, registration mode) but adds little beyond what the schema documents, so the baseline of 3 applies.

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 ('Create') and resource ('SIP Voice IN Trunk (inbound voice trunk)') for the authenticated customer. It explicitly distinguishes itself from sibling creators by naming create_pstn_trunk and create_phone_systems_trunk, so an agent can route correctly without opening schemas.

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?

Provides clear when-to-use guidance ('minimal trunk only needs name and host'), an explicit guardrail ('Set ONLY the parameters the user explicitly asked for and never invent values'), and names the alternative tools for PSTN forwarding and phone.systems trunks. It also explains the registration-mode branch (set enabled_sip_registration true and omit host/port).

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