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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses the model-vs-frequency fallback, the exact return shape { keywords, source }, the per-call price of 10 credits with a CAD-cent conversion, and that schema-invalid input is rejected before billing. Those are the billing and reliability facts an agent needs before spending credits.

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 dense sentences with no filler: the capability and its verbatim guarantee come first, then the return contract, then cost and failure handling. Slightly packed, but every clause carries information.

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?

With no output schema, the description supplies the return shape and the `source` discriminator, plus pricing and rejection semantics — everything needed to call it and interpret the result. Nothing material is missing for a two-parameter read-only tool.

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 both `max` and `text` are already fully documented in structured fields, including the 8,000-character cap and redaction behavior. The description only echoes 'up to `max` phrases' and adds nothing about format or syntax beyond the schema, so the baseline 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 the resource concretely: key phrases of the input text, and adds the defining property that each phrase appears verbatim in the source. That distinguishes it in spirit from entity-extract or summarize, but no sibling is named explicitly, so an agent must infer the boundary.

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?

No statement of when to prefer this over the many nearby text tools (entity-extract, summarize, text-stats, find-similar). The only conditional guidance is internal behavior of the tool (fallback to frequency ranking), not tool selection.

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