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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, so the safety profile is covered. The description adds useful behavioral context by specifying the validation method: structural layout plus a mod-36 cross-sum checksum, which clarifies what 'validate' means here.

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?

A single sentence that is front-loaded with the purpose and is free of filler. Every clause adds information needed to understand what the tool does.

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 one-parameter validator with rich annotations and an output schema, the description is sufficiently complete. It covers purpose and validation logic, and the output schema handles return-value details, so no critical information 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 single gstin parameter is already documented. The description adds value beyond the schema by breaking down the GSTIN structure (state code, PAN, entity code, 'Z') and noting the checksum, giving the agent a clear mental model of the input.

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?

States a specific verb ('Validate') and resource ('Indian GSTIN'), and immediately names the exact format it checks (2-digit state code + PAN + entity code + 'Z') and the checksum algorithm. This distinguishes it from sibling validators like iban_check or swift_bic_check by the precise identifier type.

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 offers no when-to-use guidance, no prerequisites, and no explicit alternatives. It does not tell the agent to choose this over batch_validate for single checks or over india_supplier_check for broader supplier validation.

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