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

readOnlyHint=true already tells the agent this is a safe read, so the bar is lower. The description adds the underlying REST call (GET /api/v3/customers/{customerId}) and the shape of the returned fields, which is useful, but says nothing about error behavior for a missing/nonexistent id.

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 action and then the endpoint reference. No filler, though the endpoint line is mildly redundant for a pure agent caller.

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 single-entity read with annotations covering the safety profile, the description enumerates the return fields and the underlying endpoint. No output schema is present, but the field list largely compensates, so an agent has enough to call it correctly.

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 coverage is 100% for the single customer_id parameter, so the schema already documents it. The description adds nothing beyond 'by id' — no format or validity notes. Baseline 3 is correct when the schema carries the parameter semantics.

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' plus resource 'a single customer' and names the returned fields (address, domain, phone, notes). The 'single customer by id' phrasing distinguishes it from the listing sibling, though it never names atera_list_customers explicitly.

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 implied by 'by id' — a lookup when the CustomerID is known — but there is no explicit when-to-use guidance or routing to atera_list_customers for enumerating customers. An agent must infer the boundary between this and the list tool.

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