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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint, so the safety profile is covered; the description's 'Side effects: none' is partly redundant. What it does add beyond the annotations is the pipeline sequencing constraint and the instruction not to prompt the user for a selection, which is genuine behavioral context.

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-loads the purpose, then the workflow constraint, then the side-effect note — a sensible order with little waste. The ordering sentence is somewhat dense with parentheses, but nothing is meaningfully superfluous.

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 need no explanation, and the description covers the workflow placement that matters most. The only gap is the lack of any note on result shape or what an empty list means, which is minor given the 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 description coverage is 100%, so both parameters are already documented, including pipeline_id's format and passthrough rule. The description only echoes that pipeline_id is optional and tied to pipeline_start, adding little beyond the schema.

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 ('List your purchased or assigned phone numbers'), which cleanly separates it from the singular get-number and the mutating update-number siblings. An agent can identify the operation without opening the schema.

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?

Gives explicit ordering guidance ('always call this after pipeline_start ... before request-file-from-user') and an explicit behavioral directive ('Do not ask the user to pick a number'). This is exactly when-to-use guidance tied to a concrete workflow, not just a vague context hint.

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