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

Annotations already declare destructiveHint=true and idempotentHint=true, and the description adds genuinely useful behavioral context on top: only non-null fields are written, and customer_billing replaces the invoice details rather than merging. What is still unstated is whether unlisted billing keys are dropped entirely and whether the call returns the updated record.

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, no filler, with the lookup and partial-update semantics front-loaded. The inline 11-key billing enumeration is dense but earns its place as the only documentation of that structure.

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 destructive mutation with zero schema descriptions and no output schema, the definition covers the core write semantics but leaves gaps: it never states that at least one of customer_id/customer_uuid is effectively required (0 required params), what customer_options controls, or what the response contains.

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 0% across 9 parameters, so the description must compensate. It documents the two lookup keys and enumerates the 11 billing sub-fields, which is real value, but customer_options is left completely opaque and note/type/email/phone/title get no format, constraint or example guidance.

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 ("Edit fields of an existing customer") plus the lookup keys, which separates it from create_customer, get_customer and delete_customer. It does not name the nearest sibling, update_customer_keys, so an agent still has to infer that boundary.

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 the verb: use it to modify an existing customer. There is no explicit when-not guidance, no prerequisites (customer must already exist), and no pointer to update_customer_keys for key/credential changes or to edit_lead for the lead-side record.

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