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

readOnlyHint=true already establishes that this is a safe read, so the description's duty is reduced. It adds the dual behavior (list vs. contact lookup) and the underlying REST mapping (GET /customers), but says nothing about pagination caps, rate-limit cost, or result ordering — all of which the schema, not the description, carries.

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 no filler; the primary list purpose is front-loaded before the secondary lookup mode. The trailing REST endpoint notation is marginally useful for agents mapping to the API but is not strictly necessary.

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 zero-required-parameter, flat-schema list tool with only readOnlyHint annotations, the description covers the two operational modes and the required parameter pairing. The absence of any statement about what a result looks like is a minor gap given there is no output schema, but the schema's pagination notes compensate.

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 six parameters are already documented at the schema level, setting the baseline at 3. The description only reinforces the contact_type/contact_value pairing with a short example ('email + an address'), adding minor value 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 ('List customers') and adds a second, clearly described mode ('find one by contact'), which an agent can distinguish from the plain listing. It does not name or differentiate from the closest sibling, enchant_get_customer, which also retrieves a single customer, leaving the boundary to inference.

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?

It tells the agent how to trigger the lookup mode (set contact_type and contact_value) and gives a concrete example, which is genuine usage guidance. It never says when to prefer this tool over enchant_get_customer or enchant_list_tickets, and there are no exclusion conditions.

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