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

Annotations already declare destructiveHint=true and idempotentHint=true, so the description's added value is explaining what 'destructive' means here: already-sent email cannot be recalled, i.e. the cancellation is forward-looking only. That is genuinely useful context beyond the annotation. It omits whether a launched campaign can be cancelled mid-send or what errors occur for already-completed campaigns.

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 short sentences, front-loaded with the action and followed by the irreversibility caveat. Nothing is wasted and there is no filler.

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 destructive mutation with seven undocumented, all-optional identity parameters, the description leaves the most consequential question unanswered: which identifier to pass and whether more than one is needed. The output schema relieves it of explaining returns, but the input side remains a significant gap for a destructive tool.

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 0% across 7 parameters, and all are optional, so the agent has no way to know which identifier is authoritative — id, campaignId, externalCampaignId, or the other external* fields. The description mentions no parameters at all and does not compensate for the coverage 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?

States a specific verb+resource: 'Stops future sends for an outbound email campaign.' That is far clearer than a restatement of 'cancel', and it scopes the effect to future sends. It does not, however, distinguish this from siblings like pause_campaign, resume_campaign, or delete_campaign, which an agent could easily confuse with it.

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 guidance on when to choose cancel over pause or delete, no prerequisites, and no note on whether the campaign must be in a particular state. The only context given is the negative consequence, which describes effects rather than selection criteria.

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