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

Annotations already establish readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered by structured data. The description adds one genuinely useful behavioral fact beyond them: the call costs 1 credit. It does not disclose the actual grade cutoffs, which is the one behavioral detail an agent cannot infer.

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?

One front-loaded sentence covering the transformation and the scale, with the cost note appended. No filler, though the parenthetical cost could be separated so it does not compete with the primary statement.

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 pure calculator with no output schema, the description is nearly sufficient — the return value (a letter grade) is clear. The missing piece is the mapping itself: 'standard grading scale' is ambiguous (90+ = A? 93+?), and out-of-range handling is unstated, which matters because the schema has no required-field enforcement.

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%, so the single parameter is already documented as a 0-100 percentage; the description merely restates 'numerical percentage score'. It does not resolve the schema's union type (number or string) or clarify what happens for out-of-range values, so it adds little beyond the schema.

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 a specific verb and both the input and output resources: converting a numerical percentage score into a letter grade on an A-F scale. This also implicitly distinguishes it from calculate_gpa, the nearest sibling, which works on a grade-point scale rather than percentages.

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?

Usage is implied by the pure-function nature of the tool (feed it a percentage, get a letter), but there is no explicit when-to-use guidance, no pointer to calculate_gpa for GPA-style conversions, and no statement of prerequisites. Nothing misleads, but nothing routes the agent either.

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