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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description adds that results are reported per code along with detected length, but it does not say what happens with malformed or partially invalid input lines, or whether one bad line fails the whole batch.

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 sentence, front-loaded with the action and the accepted code families, followed immediately by what is returned. No filler or redundant restatement of the tool name.

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 validator with no output schema, the description covers both the input constraint and the shape of the answer (check-digit verdict plus GTIN length). The remaining gap is error/batch behavior for invalid inputs, which matters given the tool accepts multiple codes at once.

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% and the single parameter already documents both the 'complete numbers' constraint and the one-per-line/comma-separated formats. The description reinforces the 'complete' requirement but adds no new syntax or formatting semantics beyond the schema.

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 concrete verb (check/validate) and the resource types (GTIN, EAN, UPC, ITF-14), and it also hints at the response shape (check-digit validity plus GTIN length). The word 'complete' scopes it away from compute-oriented siblings like calculate_check_digits and repair_gtin, but no sibling is named explicitly.

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: 'complete' numbers signals this is for validation rather than check-digit calculation or repair, which is useful routing information. There is no explicit when-to-use, when-not, or named alternative among the many siblings such as identify_code or repair_gtin.

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