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

Annotations only declare the generic safety profile (readOnlyHint=false, openWorldHint=true, idempotentHint=true). The description adds materially: a real email is sent under the business's name, the call is refused for duplicate/campaign-existing recipients, it is rate limited to 10 per minute, and it requires a Pro plan. These are exactly the traits an agent cannot infer from the structured fields.

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?

Four short sentences, front-loaded with the action, then the user-confirmation requirement, then failure modes, then rate and plan limits. No sentence is redundant.

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 mutation tool with no output schema, the description covers side effects, refusal cases, rate limits, and plan gating, which is strong. It stops short of saying what a successful call returns or where the invitation state becomes visible, a minor remaining gap.

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 100%, so name, email, and campaignId are already documented. The description adds only a soft constraint (verify the address and campaign with the user) and no format or semantic detail beyond the schema, which is the expected baseline-3 case.

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, and scope: email ONE person an invitation to join a campaign as an affiliate. The 'one person' scope distinguishes it cleanly from list_affiliates and update_affiliate_status, and no sibling performs the same action.

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?

Gives explicit preconditions (confirm address and campaign with the user first) and explicit refusal conditions (already on campaign, already has a waiting invitation), plus a plan prerequisite. The only gap is that it never names an alternative tool for adjacent tasks such as bulk or re-inviting.

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