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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, but the description adds what annotations cannot: the change propagates to every campaign sharing the mailbox, and the warm-up interaction carries deliverability risk. That is exactly the blast-radius and side-effect context an agent needs before mutating shared sending infrastructure.

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 sentences, front-loaded with scope before exclusions before risk. Every clause earns its place — no restatement of the title, 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?

Strong for a 9-parameter mutation with no output schema: scope, exclusions and risk are all covered. The remaining gap is that it never says whether omitted fields are left untouched (partial vs. full replacement) and says nothing about the return payload, though idempotentHint=true softens the former.

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 100%, so delay, replyTo, isPaused, isWarmup, signature, emailsPerDay and emailAccountId are all documented in-schema; the description's field list mostly restates them with no added format or boundary detail. Notably it omits firstName/lastName, two mutable parameters the schema does expose.

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?

Opens with a specific verb plus resource ("Change sending behaviour for a mailbox") and immediately enumerates the mutable facets: daily volume, inter-send gap, reply-to, signature, warm-up, pause state. It also draws a bright line against the lookalike siblings it is not (email_account_oauth_url, email_account_add_imap, campaign_update), so an agent can route 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 scopes the blast radius ("Affects every campaign using the mailbox, not one campaign") and names three alternatives with the condition that selects each — connecting a mailbox vs. assigning a campaign vs. this tool. It even carries a conditional warning for the risky case (raising volume on a cold mailbox).

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