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

Annotations indicate this is a write operation (readOnlyHint=false), non-idempotent. Description adds the crucial behavioral detail that provisioning incurs a monetary cost, which is not in annotations. This is significant context for an agent to avoid wasteful calls.

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?

Two sentences, front-loaded with the purpose, followed by the cost warning and selection guidance. No fluff, each sentence earns its place.

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?

With an output schema present, return values are covered. The description covers purpose, cost, and selection constraints. It does not explicitly mention prerequisites like agent existence, but that is implied by the required agentId. It is sufficiently complete for an agent to use 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 parameters are well-described in schema. Description mentions the constraint parameters but adds little beyond the schema's descriptions, which already cover them. Baseline of 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?

Clearly states a specific verb (provision) and resource (phone number), and explains it assigns to an agent. Distinguishes from siblings like phone_number_list and phone_number_release by indicating it creates a new number.

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 explicit guidance on when not to call (do not call speculatively) and how to constrain selection (use countryCode / areaCode / capabilities). Does not explicitly mention alternatives, but the context of cost and constraints implies appropriate usage.

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