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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: it is a dry-run that does not debit, and it returns cost, balance, and would_succeed. This goes beyond the annotations and helps the agent understand the operation's side-effect-free nature.

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 sentences with no filler. The core behavior ('Dry-run cost for an op without debit') is front-loaded, and the return values are listed compactly. Every word 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?

For a simple read-only quote tool with one optional parameter and no output schema, the description is nearly complete. It states the endpoint, the side-effect-free nature, and the return fields. The only minor gap is that it doesn't describe the format or structure of the returned cost/balance/would_succeed values, but that is not critical for a tool this simple.

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 coverage is 100%, so the schema already documents the 'op' parameter. The description mentions 'op=smoke' and says it defaults to smoke, which adds a small hint about the default value. However, it doesn't explain what other values might be valid or how the parameter affects the quote, so it adds only marginal value 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?

The description states a specific verb ('Dry-run cost'), a resource ('an op'), and the key behavior ('without debit'), and even names the endpoint (GET /credits/quote?op=smoke). It clearly distinguishes this from sibling tools like checkout_credits and confirm_credits by emphasizing that no debit occurs.

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 clearly implies this is for checking cost and feasibility before committing to an operation, and the 'without debit' phrasing signals when to use it instead of checkout/confirm. It does not explicitly name alternatives or state when not to use it, but the context is clear enough for an agent to select it appropriately.

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