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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description earns credit for disclosing the method (mod-10 with odd x1 / even x3 weighting), which tells the agent the tool verifies structural validity only and will not confirm the barcode is registered or in use.

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 verb and resource, with the checksum rule appended as the operative caveat. Nothing is wasted and nothing important is deferred.

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?

With a single fully documented parameter, full annotation coverage and an output schema handling return values, the description supplies nearly everything needed. Only the failure behavior on malformed or non-digit input is left implicit.

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 schema itself documents the single 'code' parameter, including that spaces and dashes are tolerated. The description adds no parameter-level detail beyond the algorithm, so it does not go past the baseline for a fully documented 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?

States a specific verb and resource ('Validate an EAN-13 barcode') and pins down exactly which check is performed (mod-10 checksum). It clearly separates itself from the many other format validators in the sibling list by naming the identifier standard, though it never explicitly contrasts itself with a sibling.

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?

There is no statement of when to reach for this versus alternatives, and no prerequisite or exclusion guidance. The only hint about applicability is buried in the algorithm parenthetical, which an agent must infer means 'checksum only, not registry lookup'.

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