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

With no annotations, the description carries the full burden of behavioral disclosure. It accurately describes the validation logic (length + checksum), the return fields (valid, type, normalized), and includes an example of a broken checksum. It does not mention edge cases (e.g., empty strings, non-digit input) but the schema already restricts to digits, so this is sufficient.

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 two concise sentences, with the primary action front-loaded. It wastes no words and includes the necessary return details and an example. Perfectly structured for quick comprehension.

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 validation tool, the description is complete. It explains the validation rules, the return object with its possible 'type' values, and provides a concrete example. No output schema exists, but the return is fully described. Nothing essential is missing.

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 parameter 'code' is already described as 'digits only'. The description adds context that the code is a product code and that validation includes checksum, but it does not add new parameter-specific semantics beyond what the schema provides. 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 clearly states the verb ('Check'), the resource ('a product code'), and the specific rules applied (length + mod-10 checksum). It also specifies the return structure, making the purpose unambiguous. Sibling tools like decode_barcode and render_barcode serve different functions (image decoding and generation), so this tool is easily distinguished.

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 implies usage: you validate a code when you have a candidate string. However, it does not explicitly mention when not to use it or provide alternatives (e.g., 'Use decode_barcode for image input'). The context of siblings helps but the description itself offers no direct guidance on selection.

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