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

Annotations already establish the safe read-only, idempotent profile, and the description adds substantive non-obvious semantics: rates are computed on delivered messages rather than recipients, and bot traffic inflates open_rate/click_rate versus the human_* variants. That is genuinely useful context an agent would otherwise get wrong, though it says nothing about freshness, caching, or permissions.

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?

Three front-loaded sentences: the returned metrics first, then the rate denominator, then the bot/human distinction. Each sentence carries distinct information, though the final clause is dense and could be split for scanability.

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 must describe the return payload, and it does so well by listing fields and explaining how rates are derived. The main omissions are the meaning/source of the id argument and any note on data freshness, which matter for correct invocation.

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 one required parameter with 0% schema description coverage, so the description carries the burden. 'For a campaign' makes it inferable that id is a campaign identifier, but the description never states the expected format or points to list_campaigns as the source of the id, leaving a real gap.

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 states a specific verb+resource ('Status and figures for a campaign') and enumerates the exact metrics returned, so an agent knows precisely what it gets back. It doesn't explicitly name the sibling it differs from (list_campaigns for discovery, send_campaign for sending), so differentiation is implied rather than stated.

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 implied: fetch stats for a known campaign id, and the description gives clear interpretive guidance on which rate to report ('human_open_rate... is the figure to give the person when they ask how many read it'). However, it never says when to call this versus list_campaigns or how to obtain the required id, so tool-selection guidance is left to inference.

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