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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered elsewhere; the description instead contributes the eligibility precondition and the concrete metric window (last 30 days, weekly deltas). It does not mention latency, refresh cadence, or whether the 30-day window is rolling, which would be useful for a reporting read.

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, front-loaded with the payload contents and followed by the use case and precondition, with no filler. The first sentence is dense but every clause names a distinct metric, so little is wasted.

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?

An output schema exists so return values need no explanation, and the description supplies the eligibility condition plus the metric inventory an agent needs to decide relevance. The one meaningful gap is sibling overlap with readDeliverability, which an agent might otherwise choose wrongly.

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?

There is a single optional parameter at 100% schema coverage, so the schema already fully documents workspaceId including the omit-when-single-workspace rule. The description only indirectly gestures at the workspace via its eligibility sentence and adds no new syntax or defaulting detail. 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?

The description names a specific resource (the email list and its recent sending results) and enumerates the contents: contacts by status, active/joined/lost counts, 30-day bounce/complaint/unsubscribe rates, reputation score, and mailbox providers. That is far more specific than a restated title. It stops short of 5 because it never distinguishes itself from the sibling readDeliverability, which plausibly covers overlapping sending-health data.

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?

"Use it to judge whether another send is welcome" gives a clear decision context, and "Only for a workspace with subscribed email contacts" states a precondition that should block a call. It does not, however, point to an alternative for workspaces without subscribed contacts or explain how it relates to readDeliverability/readCampaigns.

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