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

With no annotations, the description carries the full burden of behavioral disclosure. It clearly states what the tool returns ('what the official pages actually say and whether the widely-quoted figure has any official source at all') and warns that 'many do not'. This gives the agent an accurate expectation of both the read-only nature and the probabilistic outcome. It doesn't mention pagination or return format, but the description's explanation is well above the minimum.

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 exactly two sentences, front-loaded with the action verb and immediately followed by return behavior and a concrete usage trigger. Every sentence earns its place; there is no fluff or repetition.

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 tool with two optional parameters, no output schema, and no annotations, the description provides a complete picture: purpose, return value, and the precise condition for invocation. It could mention what happens if the tool slug is invalid or whether output is a structured object, but the absence of an output schema lowers the bar, and the description addresses the core needs well.

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?

The schema already covers both parameters fully: lang has enum/default, tool has a description including the 'omit to list' behavior. The description adds context about claim examples but does not add new parameter semantics beyond the schema. Baseline for 100% coverage is 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 opens with a specific verb-resource pair, 'Fact-check a circulating claim about an AI tool's free tier', and clearly distinguishes itself from siblings like compare_free_tiers or get_free_tier_limit by focusing on verifying sourcedness against official pages. It also clarifies the tool's unique value: identifying whether widely-quoted figures have any official source, which many do not.

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 explicitly states when to use the tool: 'Use this when a user cites a specific number... and you need to know whether it is sourced or folklore.' This is clear contextual guidance. However, it does not explicitly name sibling tools as alternatives or state when not to use it, so it falls short of a 5.

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