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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: it explains that 2021+ serials are randomized and cannot be decoded, that the lookup is advisory, and that it cannot verify condition, Activation Lock, or possession. This goes beyond the annotations and helps the agent set expectations.

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 compact and front-loaded: it states the core purpose first, then the key nuance about randomized serials, then the return value, then limitations. Every sentence earns its place, and the structure is easy to scan.

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 single-parameter read-only lookup with no output schema, the description is quite complete. It covers what the tool returns (model, market block, Macfax report existence), the serial format, and limitations. The only minor gap is not explicitly naming sibling tools for alternative actions (e.g., get_mac_report for verification), but the context signals and the description's mention of Macfax reports make the intended use clear.

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%, so the schema already documents the 'serial' parameter well. The description adds meaningful context about the serial format (10 characters on 2021+ Macs, letter first never a vowel; 11-12 on older ones) and the significance of randomized serials. This enriches the parameter semantics beyond the schema's basic type/description.

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 the tool's function: resolving a Mac serial number to its exact model, including the 2021+ randomized serials. It also distinguishes itself from sibling tools by mentioning what it returns (model, market block, Macfax report existence) and what it cannot do (verify condition, Activation Lock, possession).

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 context on when to use this tool (to resolve a serial to model and market value) and explicitly notes limitations (advisory, cannot verify condition/Activation Lock/possession). It doesn't explicitly name alternative sibling tools, but the context signals and the mention of Macfax report existence imply when a Macfax report would be needed. Slight gap: no explicit 'use get_mac_report instead for verification' routing.

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