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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds 'Side effects: none (read-only)', which reinforces but does not extend beyond the annotations. No contradiction, but no additional behavioral detail like pagination or filtering behavior.

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?

The description is two concise sentences plus a short side-effect note. It is front-loaded with the primary purpose, then gives targeted usage guidance. No filler or redundancy.

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 simple read-only list tool with an output schema and strong annotations, the description covers the core purpose and a critical workflow dependency. The only gap is not differentiating from list-shop-numbers, but that is a minor omission given the overall clarity.

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% and both parameters have descriptions in the schema. The description adds context about pipeline_id (used after pipeline_start) but this is already implied by the schema. It does not add significant new meaning beyond the schema, so 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?

The description clearly states the verb 'List' and the resource 'purchased or assigned phone numbers', which distinguishes it from list-shop-numbers (shop numbers) and get-number (single number). The purpose is unambiguous, though it does not explicitly name sibling alternatives.

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 usage guidance for the fax-sending workflow: 'always call this after pipeline_start (optional pipeline_id) before request-file-from-user' and instructs not to ask the user to pick a number. However, it does not cover when not to use this tool or compare with list-shop-numbers, so it's not fully comprehensive.

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