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

The description states the tool 'validates structure only,' aligning with the readOnlyHint annotation. It clarifies there are no side effects, but it could further disclose the exact return format or error behavior.

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 concise with two sentences, front-loading the imperative usage instruction. Every sentence adds essential information without redundancy.

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 description explains the tool's input and validation logic but does not describe the expected output (e.g., boolean, status code) or potential errors. Given the lack of an output schema, this omission limits completeness.

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?

With 100% schema coverage, the schema already explains the 'egn' parameter. The description adds value by explaining the validation logic (10-digit form and check digit), helping the agent understand what the tool checks beyond the parameter type.

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 purpose: to verify the structure of a Bulgarian EGN, specifying it checks the 10-digit form and weighted mod-11 check digit. This distinguishes it from sibling validation tools for other identifiers.

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 explicitly says 'USE THIS to verify a Bulgarian EGN before relying on it,' providing clear context for when to use it. However, it does not mention when not to use it or suggest alternatives, which would be helpful given the many sibling validation tools.

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