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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent write. The description adds real value beyond that: the feature-gate precondition and its failure mode ('error is returned and nothing is created'), and that no host/destination is required. It stops short of noting that a non-idempotent create with a unique name can fail on retry.

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?

Four tight sentences: purpose first, then the precondition, then the 'no host/destination' clarification, then routing alternatives, then return value. No filler, and the constraints are 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?

Despite 11 parameters and no output schema, the description covers precondition behavior, siblings, and return shape ('created trunk id and key attributes'), while the schema handles all field semantics. Nothing an agent needs to invoke this 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 coverage is 100%, so every parameter including enums, ranges, defaults and patterns is already documented in the schema. The description only adds the negative fact that no host or destination parameter is needed. 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?

States a specific verb and resource ('Create a phone.systems™ Voice IN Trunk') and clarifies the routing scope (assigned DIDs' inbound calls to the customer's cloud PBX). It explicitly distinguishes itself from create_sip_trunk and create_pstn_trunk, so an agent can pick it without opening sibling 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?

Names both alternative tools and the condition that selects them, and adds an explicit when-not: the phone.systems™ feature must be enabled or nothing is created. This is exactly the routing guidance an agent needs.

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