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

No annotations exist, so the description must carry the behavioral burden, and it does disclose the important traits: stateless server (stores nothing), baseline behavior on first call, and a per-call volume constraint of 3 domains. Missing is what actually happens when more than 3 domains are passed (hard error vs. paid tier) and whether the operation is strictly read-only. Still well above the bar for an unannotated tool.

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 tight sentences with no filler. The only ordering nit is that the pricing/limit note leads before the tool's actual purpose is stated, so an agent's first read is a billing constraint rather than what the tool does.

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?

With no output schema, the description carries the return-value explanation and does so adequately: a baseline on the first call, snapshots for later calls, and a change report thereafter. The shape of the diff itself (per record type, per domain) is implied but not specified, which is a minor gap for an agent parsing results.

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 3 is the baseline, but the description adds a non-obvious mapping: the `snapshots` object from the response becomes the `previous` input, and it must be omitted on run one. That round-trip relationship is not derivable from the schema alone. The 3-domain limit is restated but the >3 case is not clarified.

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 and resource: reports DNS/email-auth record changes (SPF, DKIM, DMARC, MX, MTA-STS, TLS-RPT, BIMI) since a previous run. The record-type enumeration makes the scope unambiguous. It does not explicitly differentiate itself from siblings audit_sending_domains or watch_sending_domains, so an agent still needs to infer how this differs from a plain audit or a watcher.

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 concrete operational flow: pass the previous call's `snapshots` object as `previous`, and the first run returns a baseline with no changes. That tells the agent how to sequence repeated calls. It stops short of stating when to pick this over audit_sending_domains or watch_sending_domains, which is the one remaining routing gap.

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