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

Annotations declare destructiveHint=true, and the description adds essentially nothing on top: it does not say whether an existing primary email is replaced, whether duplicate addresses are rejected, what permissions are required, or what the response contains. Only the optional primary flag adds slight behavioral color.

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 compact sentences with the purpose front-loaded; the trailing 'Shopmonkey: POST /v3/customer/:id/email' is essentially redundant with the schema's customerId/email params but costs little and confirms the target resource.

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 mutating tool with a destructiveHint, five parameters, and no output schema, the description leaves key questions unanswered: what happens to the prior primary address, what a duplicate email does, and what the call returns. The agent has enough to call it, but not enough to predict its effects.

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. The description restates only the 'primary' option without adding format or behavioral detail, so the baseline 3 applies.

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+resource ('Add an email address to an existing customer') and clarifies the optional primary semantics. It implicitly distinguishes itself from create_customer/update_customer, but never names a sibling, so it stays at 4 rather than 5.

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 phrase 'to an existing customer' hints at the precondition that the customer must already exist, but there is no explicit when-to-use guidance and no reference to alternatives such as update_customer or create_customer for other cases.

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