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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety and repeatability profile is covered. The description adds nothing beyond that — no not-found behavior, no precedence rule when both ids are supplied, no return-shape note — so with annotations doing the heavy lifting a 3 is right.

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?

One front-loaded sentence, zero filler, with the resource and lookup keys in the first clause. Nothing is 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?

No output schema exists, so the description could have said what a customer record contains, and the 0%-coverage parameters with no required fields leave the invocation contract under-specified. Adequate for a trivial getter but with clear gaps.

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 0%, so the description must compensate. Naming both 'customer_id' and 'customer_uuid' and framing them as alternatives ('or') is useful, but it leaves critical ambiguity: both are nullable with zero required parameters, and nothing says whether they are mutually exclusive, which wins if both are passed, or what happens if neither is passed.

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 ('Fetch') and resource ('a single customer') and names the lookup keys, which cleanly distinguishes it from list_customers and edit_customer. It stops short of naming a sibling explicitly, so it earns a 4 rather than a 5.

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?

Usage is only implied: the agent can infer it needs an identifier for one customer and that list_customers handles bulk retrieval, but the description never says when to prefer this over list_customers or what to do when no identifier is known.

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