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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the 'Read-only' sentence adds little. The description does add useful context by defining 'billing client' and stating the returned information, but it does not meaningfully describe behavior beyond what annotations and the output schema already convey.

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?

The description is two short sentences with no waste. The primary purpose is front-loaded, the domain clarification is embedded as a parenthetical, and the 'Read-only' note is a concise safety signal.

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 get-by-id tool with a full input schema and an output schema, the description is sufficient. It does not explicitly note that this returns a single record as opposed to a list, but the phrase 'one billing client by id' already makes that clear. Minor room remains to name client_get_list_clients as the list alternative.

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%: the single 'id' parameter is fully documented as a UUID value wrapper. The description merely says 'by id', which is consistent with the schema but does not add extra meaning beyond the parameter's existing documentation.

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 a specific verb and resource ('Returns one billing client by id') and clarifies what a billing client is ('the customer a company invoices'), including the return scope ('contact and address details'). This clearly distinguishes it from list-oriented siblings like client_get_list_clients.

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 gives clear context: this is for retrieving exactly one client by id. It does not explicitly name client_get_list_clients as the alternative for multiple clients, but the contrast between 'one' and the sibling's 'list' naming is strong enough for an agent to infer the correct choice.

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