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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavior: 'Nothing is sent', the state precondition on the target campaign, and the concrete 409 failure mode plus the list-pollution consequence of not using it. It stops short of noting auth/permission requirements, so not a full 5.

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?

Very dense and front-loaded: the resource scope leads, then the field list, then the alternative and the failure condition. Every clause earns its place, though the stacked constraints in one long sentence make it slightly harder to scan than an ideal definition.

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 7-parameter mutation tool with no output schema and low schema coverage, the description covers the critical unknowns: what is mutated, that nothing is dispatched, the allowed object state, and the alternative tool. Remaining gaps (unspecified fields are presumably left untouched, per idempotentHint) are minor.

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 coverage is only 14% (just `text`), so the description carries real weight: it enumerates the editable fields and maps API fields to parameter names ('sender' -> `from`, 'content' -> `text`), which the bare schema does not. It does not describe formats or say anything about the required `id`, so it is helpful but not exhaustive.

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 (edits), a specific resource and scope (a DRAFT campaign), and enumerates the editable fields. It is immediately distinguishable from create_campaign and send_campaign, so an agent can select it without opening any schema.

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?

Explicitly names the alternative ('Prefer it to create_campaign to rework a text') and the reason ('otherwise the old draft stays in the list'), and states a hard exclusion: scheduled/sending/sent campaigns cannot be edited and return 409. Both when-to-use and when-not-to-use are covered.

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