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 description's burden is lighter. It adds genuinely useful behavioral context beyond the annotation: the returned `id` is the key consumed by job/task creation calls, which is the main reason to call this tool. It does not discuss missing-customer behavior or rate limits.

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 sentences, both front-loaded: the core fetch semantics first, then the downstream id linkage. No filler, and the raw HTTP endpoint is appended compactly at the end.

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, and the description compensates by telling the agent the salient return field (`id`) and its purpose. Combined with the readOnly annotation and 100% schema coverage, an agent has enough to call this correctly; only edge-case behavior (not-found handling) is unaddressed.

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%, so both parameters are already documented in the schema, setting the baseline at 3. The description restates four of the six `include` enum values (contacts, jobs, tasks, notes) but omits tax_entity and custom_field_assignments, adding no new syntax or semantics beyond the schema.

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 and resource ('Fetch one customer by customer number') and scopes it to a single record, which cleanly separates it from the sibling list_customers. The optional include set is named, so an agent knows the shape of the call before opening the schema.

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?

Gives a concrete downstream usage rule: the result's `id` is what job/task create calls need as `customer_id`. That is real routing guidance. It does not, however, explicitly say when to prefer this over list_customers or how it relates to update_customer, so it stops short of full when/when-not coverage.

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