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

With no annotations, the description carries the full burden and does well: it discloses the per-call cost ($0.0029), the return range (0-96) and the success sentinel (valid=1), plus the Rust WASM engine. It omits error behavior for non-alphanumeric input, which keeps it below a 5.

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?

Four short clauses, each carrying information (cost, operation, return contract, use cases). The cost notice is front-loaded where an agent will see it before invoking a paid tool. No filler.

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?

No output schema exists, and the description compensates by stating the return value range and the valid sentinel. For a single-parameter primitive that is nearly complete; only failure/edge-case behavior for invalid characters is unaddressed.

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?

One parameter with 100% schema coverage, so the schema already documents 'input'. The description adds little beyond restating that the string is alphanumeric and that the remainder is computed over the whole string; baseline 3 applies.

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?

Specific verb and resource: 'Calculate ISO 7064 Mod 97-10 remainder for any alphanumeric string'. This is clearly the low-level primitive behind sibling tools like iban_check and lei_check, and the phrase 'custom identifier validation' hints at that generic scope, 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?

'Used for IBAN, LEI, and custom identifier validation' implies the domain of application, but it does not tell the agent when to call this primitive versus the dedicated iban_check or lei_check siblings. No exclusions or prerequisites are stated.

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