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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the read-only sentence largely restates structured data. What the description genuinely adds is the cost model ("1 credit per request") and the scope of what comes back ("public data"), neither of which appears in annotations or schema — valuable for a metered API.

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 with the resource and lookup key front-loaded, followed by safety and cost. No filler, no restatement of the title, and each clause carries a distinct fact.

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 one-parameter, non-destructive lookup with no output schema, an agent has everything needed to invoke it: what it returns (public profile data), that it is free of side effects, and its credit cost. Only the shape of the returned profile fields is unspecified, which is a minor gap given there is no output schema to consult.

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 description coverage is 100% and the single parameter already documents the flexibility of the input (with or without @, or a full x.com profile URL). The description only echoes "by handle" and adds no format, encoding, or error-case 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 ("Fetch an X user profile") plus the lookup key ("by handle"), which separates it from list-style siblings like x_get_followers or x_get_user_tweets. It never names x_search_users, so the boundary between exact-handle lookup and user search is left implicit.

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 phrase "by handle" implies the precondition that you already have a handle or profile link, and the sibling set makes the adjacent tools guessable. There is no explicit when-to-use / when-not-to-use statement and no named alternative for fuzzy name lookups.

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