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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the agent knows it is a safe, deterministic lookup. The description adds a valuable behavioral constraint (no fabricated fallback), but with no output schema or return format details it does not add rich enough context to exceed a 3.

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?

Three short sentences, front-loaded with the trigger condition, followed by the behavioral boundary. No filler, no repetition of the schema.

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 one-param lookup with a full annotation set and no output schema, the description covers the trigger, the semantic purpose, and the failure behavior. It is a bit thin on what 'Market' concretely means, keeping it from a 5.

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% for the single 'zip' parameter ('5-digit US ZIP code'), so the schema fully documents the input. The description adds meaning by tying the ZIP to 'geographic ownership', but provides no format or validation beyond what the schema already states. Baseline 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 states a specific verb+resource ('find' + 'canonical customer Market') and the triggering input ('US ZIP'). It distinguishes itself from the read-oriented siblings by its mapping/normalization purpose, though without explicitly naming those siblings a 5 is not warranted.

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?

It provides explicit when-to-use context ('when the user provides a US ZIP and WCS needs the canonical customer Market') and a negative boundary ('Does not invent a Market when geography cannot answer'), which tells the agent not to force a result. No named alternatives are given, so it falls short of a 5.

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