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

Annotations already declare readOnlyHint=true, and the description adds the endpoint detail ('POST /v1/customers.get') and optional expansion behavior. It does not contradict annotations, but it also doesn't add substantial behavioral context beyond what the annotation provides.

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 primary action and resource. The endpoint reference is useful context without adding bloat.

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 read-only fetch tool with only two parameters, the description plus schema fully cover what an agent needs: what to fetch, how to identify it, what options exist, and the fact that the operation is read-only.

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 documentation already covers both parameters fully. The description adds meaning by naming the expandable related data (invoices, entities, subscriptions, balances), which maps directly to the expand parameter and clarifies its purpose.

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 uses the specific verb 'Fetch' and names the exact resource ('a single Autumn customer'), scoped by id and with optional expansion. This clearly distinguishes it from siblings like list_customers or get_or_create_customer.

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 clearly implies usage for retrieving one customer by id, which is the core selection context. However, it does not explicitly mention alternatives or exclusions, such as when to prefer list_customers or get_or_create_customer.

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