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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is covered. The description goes beyond them by disclosing the exact return payload (verbatim definition, chapter, other books, checkable claim, related terms, links) and a non-obvious fallback: unknown terms return every term with aliases. Useful added behavior, though no auth/rate-limit nuances.

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?

Purpose and trigger are front-loaded, and every sentence carries information. The parenthetical list of example terms and the enumerated return payload make it longer than strictly necessary, but not wastefully so.

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 steps in to describe the return shape, the citing/links block, and the unknown-term fallback path. Combined with the trigger guidance, an agent has everything needed to call this 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?

Only one parameter and schema description coverage is 100%; the schema already documents that it accepts a term, alias, or slug with examples. The description's term examples overlap with the schema's own examples and add no new syntax or matching rules, so the baseline 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?

The description gives a specific verb+resource ('the definition of a term one of the Greenlit books coins or pins down') and grounds it with concrete examples of terms, so the agent knows exactly what domain this covers. It does not, however, differentiate itself from the sibling get_concept, which sounds like a potentially overlapping lookup, so it falls short of a 5.

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 states clear trigger conditions: 'when someone asks what a term means, asks you to define it, or uses it and you want the source.' That covers the common invocation contexts well, but it names no exclusions or alternatives (e.g., get_concept vs. define_term), so an agent must infer the boundary itself.

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