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

readOnlyHint=true already tells the agent this is a safe read. The description adds genuine value by enumerating returned fields (criteria, match type 0/1, readable description), but omits pagination, result caps, or error behavior for an unknown list ID.

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?

One front-loaded sentence stating scope and returned fields, followed by the backing endpoint. Little waste, though the raw endpoint path is marginally redundant for an agent that doesn't need it.

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 correctly compensates by naming the fields returned, and the single required parameter is fully covered by the schema. Only missing pagination/edge-case notes keep it from a 5.

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 coverage is 100% and the single mailing_list_id parameter is already documented (GUID, sourced from moosend_list_mailing_lists). The description adds nothing beyond what the schema provides, so the baseline 3 is correct.

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 resource (segments of one mailing list), plus what the results contain (criteria, match type, description). It implicitly distinguishes itself from moosend_get_segment by scope ('one mailing list'), though it never names that sibling explicitly to fully earn a 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?

Usage is only implied: an agent can infer you call this to enumerate a list's segments, and that moosend_get_segment handles a single one. There is no explicit when-to-use, when-not, or named alternative, so it stays at the minimum-viable level.

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