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

Annotations flag destructiveHint=true, and the description adds the crucial non-obvious semantics that annotations cannot convey: unspecified fields are left alone, but a passed address replaces the stored one whole, forcing a read-back-and-resend workflow. It does not cover permissions/auth requirements or what happens on an unknown customer ID, so not a full 5.

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 sentences, each carrying a distinct constraint, front-loaded with the operation and back-loaded with the escape hatches (read-back, notes elsewhere). No filler.

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 mutation tool with no output schema and nested objects exposed, the description covers the destructive replace behavior and the ID sourcing that would otherwise cause data loss. Missing only error/permission outcomes, which is a minor gap.

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 only 43%, but the description compensates for the riskiest gap: the billing/shipping objects are write-whole, not field-merged, and the customerId must be an ID rather than a name. The remaining scalar fields (email, phone, firstName, lastName) are self-explanatory and left to the schema, which is acceptable.

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 contact details on an existing customer') and immediately distinguishes itself from siblings by naming get_customers as the ID source and add_customer_note for notes. An agent can tell this apart from hub_create_customer, hub_delete_customer, and hub_add_customer_note without opening a 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?

Explicit prerequisites and routing: take the ID from get_customers (never a name), read the address back with get_customer before passing one, and notes must go to add_customer_note instead. Covers both when-to-use and when-not-to-use with the named alternative.

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