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

Annotations already declare readOnlyHint=true and idempotentHint=true, reducing the burden on the description. The description adds behavioral context by specifying the return payload ('Returns isValid, discount amount, and an error code/message if invalid'). This is valuable beyond annotations, though it doesn't cover edge cases or error specifics.

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 concise sentences with the purpose front-loaded. No filler or redundancy. Every word adds value, delivering purpose, return info, and usage guidance in less than 30 words.

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?

The tool has an output schema, complete parameter documentation, and read-only annotations. The description covers purpose, usage, and return behavior, which is sufficient for a simple validation tool. Minor gap: 'given order' is not formally tied to the parameters, but this is a minor ambiguity given the schema and context.

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 schema already documents all parameters. The description adds minimal param context ('for a given order') but doesn't clarify how amount, channel, or accountId map to an order. Baseline 3 applies since the schema does the heavy lifting and the description adds no significant param meaning.

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?

Description opens with a specific verb+resource: 'Check if a promotion code is valid for a given order.' This clearly distinguishes it from sibling tools like create_promotion, get_promotion, and validate_campaign. It also states the return values (isValid, discount amount, error code/message), making the purpose unmistakable.

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?

Provides clear usage context with 'Use before applying to a checkout.' This tells the agent when to invoke the tool, but it does not explicitly mention when not to use it or name alternative tools. The guidance is sufficient for the primary use case but lacks exclusionary details.

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