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

With no annotations provided, the description carries the full burden of behavioral disclosure. It describes the core verification and normalization behavior, but it does not specify what happens for invalid ISBNs, the exact return format (e.g., boolean vs. normalized string), or whether input formatting like hyphens is handled. This is adequate but leaves key behavioral details unspecified.

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?

The description is well-structured with a concise opening sentence and clear bullet lists for usage. Every sentence serves a distinct purpose, with no fluff or repetition. It is appropriately sized for the tool's simple one-parameter design.

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 simple validation tool with one parameter, the description covers purpose, usage scenarios, and exclusions well. The only gap is the lack of detail about return behavior or edge-case handling, but given the tool's low complexity and the schema's full parameter coverage, it is mostly complete.

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?

The schema already provides 100% coverage for the single parameter 'value' with description 'ISBN-10 or ISBN-13 candidate'. The description's mention of verifying and normalizing an ISBN-10/13 string adds only marginal context beyond the schema, so the baseline score of 3 is appropriate.

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 explicitly states the tool 'Verify whether an ISBN-10 or ISBN-13 passes checksum rules and return normalized digits', using a specific verb and resource. It also distinguishes itself from sibling tools by naming alternatives like uuid_validate and luhn_validate in the exclusions, making its purpose unmistakable.

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 provides clear 'Use when' and 'Do not use when' sections. It gives concrete scenarios ('Check the checksum for an ISBN-13 book identifier') and explicitly names alternative tools for other validation tasks, offering strong guidance on when to use this tool versus others.

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