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

Annotations already declare read-only, idempotent, open-world and non-destructive, but the description adds behavior the annotations cannot: a batch cap of 20 replies per call, a cost of 1 credit, an entitlement requirement, and the exact failure mode for trial keys. That is precisely the operational context an agent needs before spending a credit.

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?

Three short sentences, front-loaded with purpose, then return shape, then cost and entitlement constraints. Every sentence carries distinct information: capability, payload, and access/pricing rules — nothing is repeated from the schema or annotations.

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?

There is no output schema, so the description compensates by naming the return fields ('text, author and engagement') and the page size. Together with the credit cost and plan restriction, an agent has everything needed to call this correctly and predict the result shape.

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 earns an extra point by stating 'One call returns up to 20 replies,' which explains why the cursor parameter exists and when to paginate — meaning the schema alone ('Pagination cursor from a previous call') does not convey.

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 opens with a specific verb+resource statement: 'Get the replies to an X post.' The platform qualifier ('X post') cleanly separates it from tiktok_comments, so an agent can route between the two comment-fetching siblings without opening either 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?

It gives a strong precondition — 'Paid plans and pay-as-you-go only — trial keys get an error (the trial is TikTok only)' — which tells the agent when this call will fail. However, it never states when to prefer x_comments over x_search or x_posts for reply data, so the alternative-selection guidance is only implied by the sibling names.

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