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

Annotations declare destructiveHint=true, yet the description never explains what is destructive—whether adding an email replaces an existing primary, how duplicates are handled, or whether permissions are required. It effectively only restates the operation and appends the REST endpoint, adding little behavioral context beyond the annotation.

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 tight sentences with the core action front-loaded and no filler. The endpoint mapping is a compact extra rather than padding, though it contributes little to selection.

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 simple add-email mutation with no output schema, the description covers the essential action, but it omits failure modes (duplicate address, missing customer), the meaning of the destructive annotation, and how primary/subscribed interact—gaps an agent would want before invoking.

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 100%, so all five parameters (email, primary, customerId, locationId, subscribed) are already documented in the schema, establishing a baseline of 3. The description echoes the primary/optional concept but adds no format, validation, or constraint detail beyond the schema.

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 ('Add an email address to an existing customer') and clarifies the optional primary-address scope. It is distinguishable from read siblings like find_customers_by_email, though it does not explicitly contrast with update_customer, which could also modify emails.

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 notes the 'optionally as their primary address' case but gives no when-to-use guidance, no prerequisites (e.g., the customer must already exist beyond the phrase 'existing customer'), and no direction toward alternatives such as update_customer.

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