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

Annotations cover read-only safety, but the description adds substantial context beyond them: the code is delivered via voice call (never SMS), a copy is emailed to the workspace owner about a minute later, codes expire within minutes, and a null code means nothing has arrived yet rather than an error. This also explains the idempotentHint=false behavior, since repeated reads can return different codes.

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?

Five compact sentences, front-loaded with the action and scope, then constraints, then return shape and retry policy. Every sentence carries operational information; nothing is redundant with the annotations or schema.

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 no output schema, the description still documents the return object field-by-field ({ code, code_received_at, messages, instructions }), explains the null case, and explains what messages is for (reading raw texts verbatim when parsing fails). Nothing an agent needs to call and interpret this correctly is missing.

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?

Only one optional parameter and schema coverage is 100%, with the schema already documenting the default to the workspace's active number. The description reinforces the 'rented number' constraint but adds no format or syntax detail beyond the schema, so the baseline of 3 applies.

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 ('Read the WhatsApp verification code Meta sent') plus the scoping constraint ('to a number this workspace rents'), which cleanly separates it from sibling listing tools like list_phone_numbers and search_phone_numbers. An agent can identify the tool's job 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 when-to-use conditions (during Meta signup, after the user requested the code by Phone call, never SMS), an explicit exclusion (a number the user owns delivers the code to their own phone), and a behavioral rule for the empty case (wait for the user to re-request rather than tight-loop retrying). Nothing about invocation timing is left to inference.

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