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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds real non-annotation context: only unarchived lists are read, the result includes an exact member count, and contacts are deliberately excluded. It does not mention failure behavior for missing/archived ids, keeping it below 5.

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 short sentences, zero filler, with the core action front-loaded and the exclusion/routing note trailing. Every clause earns its place.

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, the description carries the return-value burden and does so: it states the member count is returned and contacts are not. Combined with annotations covering the safety profile and a fully documented single parameter, an agent has everything needed to call this correctly.

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 the sole list_id parameter is already documented with UUID format and an example. The description contributes no additional parameter meaning (no constraints on archived ids, no format notes), 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?

The description gives a specific verb and resource ('Read one unarchived list in the selected product') plus scope details (unarchived, selected product, exact member count). It also explicitly distinguishes itself from list_list_contacts, so an agent can separate it from a large sibling set without opening schemas.

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 provides an explicit when-not and names the alternative: 'Does not return contacts; use list_list_contacts.' That is clear routing guidance. It lacks a positive statement of when to prefer this over list_lists or get_product_context, so it stops short of full when/when-not/alternatives coverage.

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