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

Annotations already declare destructiveHint=true, idempotentHint=false and readOnlyHint=false, so the safety profile is covered. The description adds genuinely new behavior beyond that: cancellation is not atomic - mail already handed to the provider cannot be recalled, only unsent mail is suppressed. It still doesn't say whether the cancel is reversible or what error states look like.

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?

One sentence, front-loaded with the action and its scope, followed by the one behavioral caveat that matters. No padding or redundancy.

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 single-parameter destructive tool with no output schema, the description plus annotations cover the essentials: what it does, what states it applies to, and the partial-cancellation caveat. Missing only secondary details such as reversibility and permission requirements.

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 parameter with 100% schema coverage, and the schema description even points to list_newsletters as the id source. The description adds no additional meaning about campaignId, so the baseline 3 for full schema coverage 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?

States a specific verb (stops) plus the resource (newsletter) and narrows the applicable states to 'scheduled or sending', which cleanly separates it from create_newsletter, schedule_newsletter, update_newsletter and preview_newsletter without needing to name them.

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?

The phrase 'scheduled or sending' gives clear context for when the tool applies, so an agent knows it should not be used on a draft or an already-sent campaign. It stops short of naming alternatives or stating exclusions explicitly (e.g. what to do for a draft, or whether update_newsletter is the right path instead).

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