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

With no annotations, the description carries the full burden. It discloses the dependency on get_connected_accounts, the behavior for omitted clerk_instance_id (default account), the return summary, and the token cost. However, it doesn't mention side effects or permission requirements beyond the inherent mutation of 'update'.

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 sentences, each with distinct purpose: action, prerequisite, return, cost. No redundant words, front-loaded with the primary verb.

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?

The description covers the prerequisite, connection targeting, return value, and cost. Combined with the complete input schema and output schema, it provides sufficient context for an agent to use the tool correctly, even though it omits explicit error cases.

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 the baseline is 3. The description adds context for clerk_instance_id by connecting it to the prerequisite get_connected_accounts call, but most parameter meaning is already in 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?

The opening sentence 'Update a Clerk phone number by id' precisely identifies the action (update), resource (phone number), and method (by id). This clearly distinguishes it from sibling tools like clerk.create_phone_number, clerk.delete_phone_number, and clerk.get_phone_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?

The description explicitly instructs to call clerk.get_connected_accounts first and explains how to target a connection via clerk_instance_id or default. It provides clear prerequisite and usage context, though it doesn't explicitly state when to use this tool over alternatives like update_email_address.

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