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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavioral information by disclosing a metered cost ('cost: 1 credit'), which annotations never express. It says nothing about output shape or edge cases (e.g. impossible sums), so it is not rich beyond that.

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?

Two short sentences with the core purpose front-loaded and the cost note clearly parenthesized at the end. No padding or redundancy, though the single-sentence purpose could have been tightened slightly by folding the faces qualifier.

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?

This is a simple, stateless pure-computation tool with no output schema and full schema coverage, so the description needn't explain return values or ordering. The only real omission is differentiation from probability_consecutive_rolls and any note on invalid inputs (target sum outside achievable range).

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%, and each parameter is documented as 'integer, required' with its role, so the schema carries the load. The description restates the semantics of num_dice, num_faces and target_sum in prose but adds no constraint, range, or validation detail beyond the schema — 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 names a specific verb ('Calculates the probability') and the exact resource ('rolling a specific sum with a given number of dice, each with a specified number of faces'), which maps cleanly onto the three parameters. It does not, however, distinguish itself from the sibling probability_consecutive_rolls, so an agent must infer the boundary between single-sum and consecutive-roll probability.

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 phrasing implicitly signals the use case (you want the probability of one target sum), but there is no explicit when-to-use, when-not-to-use, or pointer to probability_consecutive_rolls for the related scenario. Selection between the two probability siblings is left entirely to inference.

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