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

Annotations only supply destructiveHint=true; the description adds that this is a partial PATCH (untouched fields are preserved) and enumerates the field classes that cannot be mutated here. It does not mention permission/auth requirements, rate limits, or error behavior, but it goes meaningfully beyond the structured 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?

Three short sentences, front-loaded with the mutation class ('WRITE:'), then the update semantics, then the exclusions, then the endpoint mapping. Every sentence carries distinct information with no restatement of the name or title.

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 32-parameter mutation tool with full schema coverage and only a destructiveHint annotation, the description covers the essentials: operation type, partial-update behavior, and scope limits. It omits what the call returns (no output schema exists) and any failure/permission notes, which keeps it short of fully complete.

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% (32 params, all documented), so the baseline is 3. The description still adds semantics the schema cannot express: that omitted parameters are left unchanged (partial-update contract) and that balances, credit limit, and custom fields are out of scope for this call.

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 ('WRITE: update fields on an existing customer') and pins the semantics as a partial update via 'Only the fields you pass change'. The 'existing customer' framing cleanly separates it from create_customer and get_customer among the siblings without needing to name them.

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 clear usage context ('only the fields you pass change') and an explicit exclusion set ('Balances, credit limit and custom fields are not settable here'), which tells the agent when this tool will not work. It stops short of naming the correct alternative for those excluded fields, so it lacks the explicit routing a 5 would require.

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