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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds useful behavior beyond that: results are compact and cited, each item carries a url, and a prepaid API key is required. It stops short of noting rate limits, whether an auth error occurs for missing keys, or pagination behavior beyond the schema's cursor field.

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 the purpose, followed by return-shape and prerequisites. The platform list is duplicated almost verbatim from the schema enum, which is mild waste but keeps the definition self-contained.

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?

For a read-only, 4-param tool with full schema coverage and no output schema, the essentials are present. Missing: why no output schema exists and what the compact item fields are beyond url, plus any behavior when limit exceeds available posts or when the account is private.

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 meaning by noting username works with or without a leading @ implicitly through "one account" phrasing and by enumerating platforms twice (description vs enum). Marginal gain — the enum and cursor semantics are already documented 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?

Specific verb+resource ("Recent public posts from one account") with scope qualifier (recent, public) and an explicit platform list. An agent can distinguish it from get_post (single post) and search_posts (query-based) 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?

The description implies usage (fetch one account's posts on a named platform) and names supported platforms, but never states when to prefer search_posts or get_user, nor any exclusions. Alternatives must be inferred from sibling names rather than from the text.

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