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

With no annotations, the description carries the full burden and does a solid job: it discloses per-call pricing, that the price applies whether or not the result is cached, and that failed calls are refunded — financial behavior an agent cannot see in the schema. It stops short of permission/auth requirements or rate-limit behavior, but the cost/caching/refund disclosure is genuinely valuable beyond the structured fields.

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?

Two sentences, zero filler. The returned-field inventory comes first, the invocation constraint and cost/refund note second — well front-loaded and dense.

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's enumeration of returned fields is exactly what an agent needs to decide whether the call answers its question. Combined with the cost and refund disclosure, nothing material for correct invocation 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?

Schema coverage is 100%, so the baseline would be 3. The description earns above baseline by stating the mutual-exclusion rule ('exactly one of url or id'), which the schema itself does not encode — required is empty and there is no oneOf/anyOf constraint. It adds no redundant restatement of the id/url/fresh fields.

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 (fetch), resource (one post), and enumerates the returned payload — text, author, created_at, public_metrics with views, media, hashtags/mentions, reply/quote parent. The singular 'one post' implicitly separates it from get_x_posts and search_x, and the retrieval key (URL or id) is given up front.

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 tells the agent to 'Give exactly one of `url` or `id`' and discloses cost (3 credits) plus refund behavior, which is useful operational context. However, it never states when to prefer this over get_x_posts, search_x, or get_x_replies — the choice among sibling read tools is left to be inferred from the name alone.

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