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

Annotations already mark the tool as read-only, idempotent, and non-destructive, so the agent knows it is a safe calculation. The description adds no behavioral context beyond the name, such as whether the estimate is approximate or depends on current pricing. It does not contradict the annotations.

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 a single, focused sentence with no extraneous words. It is front-loaded with the verb and object. While it is brief, this is not a flaw; it earns its place.

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?

Despite having six parameters and no output schema, the description does not clarify what the tool returns (e.g., a numeric credit amount, a breakdown) or how the estimate is computed. The annotations cover safety but not functional expectations. This leaves the agent guessing about the tool's output.

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?

The input schema provides 100% coverage of all six parameters with descriptive details (e.g., operation enum values, duration constraints, generate_audio doubling cost). The description adds no additional parameter semantics, so the baseline score of 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 clearly states the tool's function: estimating credit cost for an operation, using the specific verb 'estimate' and resource 'credit cost'. It is distinct from sibling tools like get_user_credits and create_credit_checkout_session, which deal with balance and purchase rather than cost estimation. However, it lacks detail on the range of operation types covered.

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 provides no guidance on when to use this tool versus alternatives. There is no mention of prerequisites, such as having an operation in mind, or exclusions like needing to check actual credit balance. Sibling tools are not referenced.

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