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

Annotations already flag destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: fields omitted are not sent, so this behaves as a partial update rather than a full replacement despite the PUT endpoint — an important clarification for an agent worried about wiping fields.

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?

Four short clauses, front-loaded with the WRITE label and the operation, then the non-obvious constraint, then the endpoint. No filler; every sentence carries information.

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 5-parameter mutation tool with full annotation coverage and no output schema, this covers operation, partial-update semantics, and the key required-field gotcha. The only real gap is guidance on choosing this tool versus create_customer.

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% and the schema already states the name is 'required by Bookafy on every update', so the description's name guidance largely repeats it. The 'fields you leave out are not sent' clause does add useful semantics about how the parameters combine, but nothing about custom_fields or the id source beyond what the schema gives.

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 ('change a customer's details') and labels itself WRITE, which distinguishes it from the read siblings like bookafy_list_customers and bookafy_get_account. It does not explicitly contrast with bookafy_create_customer, so the create-vs-update distinction is left implicit.

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 real procedural guidance ('pass the current name when you only change the email or phone') and clarifies partial-update semantics. However, it never says when to choose this over bookafy_create_customer or bookafy_list_customers, nor what preconditions (e.g. the customer must already exist) apply.

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