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

Annotations already declare readOnly, idempotent, non-destructive. The description adds key context: 'Keyless/offline' (no side effects), 'Spaces/dashes ignored' (input processing), and 'Validates the number, not the device' (scope limitation).

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 efficient sentences, front-loaded with the core purpose. Every sentence adds value: validation method, input handling, output details, and scope clarification.

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 validation tool with one parameter and no output schema, the description fully explains input handling, validation logic, and the components of the result (validity, TAC, serial, check digit). It also clarifies what the tool does not do.

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% for the single parameter, but the description adds useful detail: allowed formats (15/16 digits), that spaces/dashes are ignored, and what the validation checks (Luhn). This goes beyond the schema's basic description.

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 it validates IMEI/IMEISV with specific validation rules (Luhn check for IMEI) and explains what it returns (validity, TAC, serial, check digit). It distinguishes from device validation by explicitly saying 'Validates the number, not the device.'

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 includes 'Keyless/offline' indicating no authentication needed, and clarifies it does not validate the device. However, it does not explicitly differentiate from sibling tool 'imei_check_digit', though the purpose is distinct enough.

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