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

With readOnlyHint and idempotentHint already covering the safety profile, the description adds real value by stating that the check digit is recalculated, that output is hyphenated, and that 979-prefixed ISBN-13s have no ISBN-10 (a failure mode to expect).

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 compact sentences with the core action front-loaded and the edge case appended; nothing is redundant or wasted.

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?

The tool is a simple one-param transform with no output schema, and the description adequately conveys the result (hyphenated form with recalculated check digit) plus the main edge case, though it could mention error behavior for invalid input.

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 'isbn' parameter already documents that hyphens are accepted, so the description adds little parameter meaning beyond what the schema provides; 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?

States a specific verb (convert) and resource (ISBN-10/ISBN-13) with bidirectional scope, which is enough to distinguish it from siblings like calculate_check_digits and validate_gtins without opening either schema.

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?

The description implies usage for converting between ISBN formats and notes the 979 edge case that makes conversion impossible, but it never explicitly routes the agent against alternatives such as calculate_check_digits or convert_upc_e, leaving selection to inference.

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