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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and closed-world scope, so the safety profile is covered. The description adds the filter families available but says nothing about result shape, maximum page size behaviors, sort defaults, or whether scores/unsubscribed filtering is exclusive — modest added context given the annotation baseline.

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?

A single sentence with zero filler, front-loading the verb and resource before the filter capabilities. Every clause maps to actual functionality exposed in 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?

For a 12-parameter read-only list tool with rich schema descriptions and no output schema, the definition covers the essential capability. The only real gap is the absence of sibling disambiguation (export vs list vs audience subscriber listing), which is minor against the well-documented schema and annotations.

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 92%, so nearly every parameter is already documented in the schema (tag, page, sort, limit, match, order, filters, score bounds, audience_id, unsubscribed). The description's mention of search, audience, subscription, and custom-field filters roughly mirrors those schema entries without adding format, defaults, or interaction rules beyond what is already stated.

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 concrete verb and resource ('List contacts') plus the filter families it supports (search, audience, subscription, custom-field), which is more than a restatement of the name. It does not, however, distinguish this tool from plausible siblings such as export-contacts, list-audience-subscribers, or get-contact, leaving the agent to infer the boundary.

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?

There is no when-to-use or when-not-to-use guidance and no sibling is named. An agent is left to guess whether to use this versus export-contacts for bulk retrieval or list-audience-subscribers for audience-scoped listing; only the tool's purpose implicitly signals it is the general contact query tool.

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