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

Annotations already declare readOnlyHint=true, so the safety profile is covered, and the description adds the underlying REST endpoint (GET /customers/external_customer_id/{external_customer_id}). It does not disclose what happens when the external id is unknown (empty body vs. 404) or any rate-limit behavior, so it adds only modest context beyond the annotations.

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 short sentences, front-loaded with the purpose and followed by the endpoint mapping. Nothing is redundant or padded.

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 one-parameter read tool with readOnlyHint and no output schema, the description covers the essentials: what it returns conceptually and which identifier to supply. The main omission is failure behavior for an unmatched external id, a minor gap rather than a blocking one.

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?

There is a single parameter with 100% schema description coverage, so the schema already documents it; the description only restates 'your external customer id'. Baseline 3 applies since the schema does the heavy lifting and the description contributes no additional syntax or format guidance.

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 pins the lookup key to the external customer id, which implicitly separates it from the sibling orb_get_customer. It never names that sibling or states the contrast explicitly, so differentiation is inferred rather than spelled out.

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 phrase 'by your external customer id' implies the selection condition for this tool over orb_get_customer, but there is no explicit when-to-use/when-not statement or named alternative. Usage is left to the agent's inference.

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