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

Beyond the readOnly/idempotent/non-destructive annotations, the description discloses valuable behavior: counts are 'when last counted,' nightly RFM segments have a key, every segment has an id, and either identifier can be used with previewSend and draftCampaign. It also states the subscribed-contacts precondition.

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?

The description is front-loaded with purpose and return information, then adds identifiers and usage context. All sentences contribute useful selector or invocation context without unnecessary verbosity.

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?

Given the output schema exists and the single workspaceId parameter is fully documented, the description supplies enough additional context about freshness, identifiers, downstream use, and workspace preconditions. Nothing essential for correct selection or invocation is missing.

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 the workspaceId semantics are already fully documented in the schema. The description does not add any further parameter guidance, so the baseline of 3 is appropriate.

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 clearly states the resource and returned data: the workspace's email segments plus subscriber counts from the last count. It also distinguishes this read operation from downstream actions by naming previewSend and draftCampaign as consumers of segment ids/keys.

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 gives a clear usage rule: use this before proposing a campaign so the audience is real rather than assumed. It also adds a constraint, 'Only for a workspace with subscribed email contacts,' but does not explicitly compare against the createSegment sibling or other alternatives.

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