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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds the cost/latency note ('Cheap — usually under 1k tokens') and clarifies the tool returns exactly one term's data, which is useful behavioral context beyond the annotations. No contradiction.

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 three short sentences with zero fluff. It front-loads the core function, then the use case, then a cost hint. Every sentence earns its place and no redundant information appears.

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?

Given the tool's simplicity, full schema coverage, and an output schema, the description covers purpose, trigger, and cost. It doesn't explicitly discuss when not to use it (e.g., for listing multiple terms) but that's a minor gap. Overall it's sufficient for an agent to call correctly.

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%, with each parameter already documented (intent enum, termSlug, subjectSlug). The description does not add parameter-specific semantics beyond what the schema provides, so the baseline 3 applies. It doesn't detract, but it also doesn't enhance.

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 and resource: 'Returns the full definition, context and related terms for one AP key term.' It clearly distinguishes this from list_key_terms by emphasizing 'one AP key term' and ties to a concrete use case ('what does X mean'), making the tool's purpose unambiguous.

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 gives an explicit trigger condition: 'Use when a student asks "what does X mean" for AP vocabulary.' It does not name alternatives or when-not-to-use, but the context is clear enough to route an agent correctly. The sibling list provides obvious contrast with list_key_terms, so a 4 is appropriate.

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