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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds the REST endpoint and a useful semantic note that the primary contact is 'copied on communications', but says nothing about pagination limits or result ordering beyond what the schema states.

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 sentences, zero filler: the resource and its returned fields come first, the endpoint last. Every clause carries information and nothing is repeated from the schema.

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?

With no output schema, enumerating the returned fields (name, title, email, phone, primary, SMS-enabled) is genuinely compensating information. Combined with comprehensive parameter schemas and read-only annotations, this covers what an agent needs, with only pagination/ordering behavior left implicit.

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% and every parameter (page, sort, per_page, customer_id) is documented in the schema itself. The description only implies that customer_id scopes the call; it adds no syntax or format detail beyond the schema, so the baseline of 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 (List) and a precisely scoped resource (contacts belonging to one customer), and enumerates the returned fields. The scope phrase 'of one customer' distinguishes it from invoiced_list_customers and invoiced_get_customer, though no sibling is named explicitly.

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 implied: fetch contacts for a known customer id. There is no explicit when-to-use guidance, no mention of when to prefer invoiced_get_customer instead, and no note about paginating through large contact lists (that detail lives only in the schema).

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