Create outbound caller ID (write)

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

The description discloses the verification call/code process, adding context beyond annotations (readOnlyHint=false, destructiveHint=false). It does not detail potential failures or costs.

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 very concise with one sentence and a follow-up note. It front-loads 'WRITE' and the main action, though could be slightly more structured.

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?

Given no output schema, the description should explain the return value but does not. It covers purpose and side effects well but omits response details.

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% with clear parameter descriptions. The description adds no extra semantic meaning beyond the schema, providing a baseline score of 3.

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 explicitly states 'Register a phone number as an outbound caller ID' with a clear verb and resource, distinguishing it from sibling tools like list_outbound_caller_ids. The title also reinforces the write nature.

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?

The description implies use when registering a new caller ID but does not explicitly state when to use or avoid it, nor mention alternatives like list_outbound_caller_ids for checking existing IDs.

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