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

The description asserts 'Calling this changes nothing', but the annotations declare readOnlyHint=false, i.e. the tool may modify its environment. These are direct, mutually exclusive claims about side effects. The rest of the disclosure (returns a preview plus a confirmation link, merchant-gated execution) is genuinely valuable, but the read/write conflict makes the safety profile unreliable.

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?

The description is short and front-loads the purpose correctly, and the preview/confirm sentences are load-bearing. The 'Money is integer minor units' sentence, however, earns nothing for a tool with no monetary argument and should have been dropped.

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 3-required-param tool with no output schema, the description usefully describes the two-step preview-then-merchant-confirms return behavior, which is the main thing an agent needs. It is undercut by the readOnly conflict: the agent cannot tell from the definition whether calling it is truly side-effect free.

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 body/email/subject are already fully documented at the field level, giving a baseline of 3. The only parameter-adjacent sentence in the description ('Money is integer minor units (cents)') refers to a field that does not exist on this tool, so it adds no meaning and is at best neutral noise.

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?

The opening sentence names a specific verb and resource ('Email a customer'), which is unambiguous and clearly separates it from siblings such as customers_note, customers_lookup, and customers_change_email. An agent can pick this tool for 'send a message to a shopper' without opening any 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?

Usage is only implied (this is the tool for emailing a customer) and the description does explain the operational flow it participates in. However, it names no alternatives, no exclusions, and no prerequisites beyond the embedded confirmation step, so an agent gets no explicit routing guidance against the other customers_* tools.

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