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

With no annotations provided, the description carries the full behavioral burden. It discloses the $0.15 cost, that it's paid from shop credits, that failed/empty calls are free, and lists the output contents (contact routes, non-LLM stats). It does not explicitly state that the tool is read-only, but a lookup tool by nature does not mutate; the cost and output disclosures go beyond minimal expectations.

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?

The description is a single, well-structured paragraph that front-loads the core purpose ('enriched PERSON CARD') and then lists key outputs with a dash-separated list, followed by cost and failure behavior. It is slightly longer than necessary but every sentence adds value—no filler. The structure aids scanning.

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 single-parameter lookup tool with no output schema, the description covers what the tool returns, its cost, how to fund it, and the free-on-failure policy. It does not detail the exact output format or data types, but without an output schema that is not strictly required. An agent has enough to call it correctly and interpret the result.

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?

There is only one parameter 'username' with a clear schema description ('X handle, e.g. naval'). Schema coverage is 100%, so the schema already documents the parameter. The tool description adds no extra semantics about format, validation, or edge cases beyond the schema, so it sits at the baseline of 3.

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 states a specific verb 'lookup' with a clear resource ('X/Twitter person'), and enumerates the enriched data delivered (name, role, company, topics, contact routes, stats). It clearly distinguishes itself from siblings like x_profile (which likely returns a simpler profile) and x_search (which searches tweets), by emphasizing the 'enriched PERSON CARD for a lead/recruiting/sales agent'.

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 explicitly targets a lead/recruiting/sales agent use case and explains cost and how to fund it (buy_credits), plus the free-on-failure guarantee. It doesn't explicitly name alternatives or when-not-to-use, but the purpose is specific enough that an agent can infer when to choose it over x_profile or x_search. A small gap is the absence of an explicit exclusion, hence a 4.

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