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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds the non-obvious detail that only the check digit is validated — not registry lookup or code existence — which meaningfully scopes the result. It still omits what happens with malformed input.

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?

One short sentence, front-loaded with the verb and covered formats, with zero filler. Nothing could be removed without losing information.

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 read-only tool with full annotation coverage, most of what an agent needs is present. The notable gap is the return value: with no output schema, the description never says whether it returns a boolean, a parsed result, or an error, which an agent needs to interpret the call.

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% and the single parameter already has an example, so the schema carries the semantics. The description adds no format or normalization guidance beyond it, which is the baseline case.

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?

Names a specific verb (validate) and resource (GTIN-8/12/13/14, EAN/UPC), and specifies that validation means the check digit. An agent can distinguish it from siblings like validate_isbn or validate_card by the identifier family named.

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?

Usage is only implied: the tool is for checking barcode check digits. Nothing says when to prefer it over validate_batch for multiple codes, nor any exclusions or preconditions (e.g. length normalization).

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