validate_isbn

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

With no annotations provided, the description carries the burden. It discloses that it checks the 978/979 prefix and mod-10 check digit, and returns the expected check digit on failure. This conveys the tool's behavior adequately.

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?

Two sentences, front-loaded with 'USE THIS'. Every word is functional; no fluff.

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, but the description explains the return behavior (returns expected check digit on failure). Could mention success return, but sufficient for a validation tool.

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 covers the isbn parameter with description. The description adds 'hyphens and spaces are ignored,' which provides input handling detail 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?

The description clearly states 'verify an ISBN-13 book identifier' and explains the checks performed (prefix and check digit). It distinguishes from siblings like validate_card, validate_iban, validate_vin which target different identifiers.

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?

Explicitly says 'USE THIS to verify an ISBN-13 book identifier instead of trusting that 13 digits are correct.' Provides clear context for when to use. Does not explicitly state when not to use, but sibling tools indicate distinct use cases.

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