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

Far exceeds the annotations: it discloses that the tool reads the current list and writes it back, that nothing is sent when nothing changes, the free-plan origin allowlist, the 402 upgrade_required error shape, and that custom domains are auto-accepted while active. Annotations say destructiveHint=false, and the description correctly clarifies that "set" replaces the whole list, so no contradiction.

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?

Front-loaded with the action, then semantics, then the trigger scenario, then plan constraints and a doc link — a sensible order. It runs long and the appended [When to use] safety boilerplate is generic across tools rather than specific to this one, which costs a point.

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 4-parameter mutation tool with no output schema, everything an agent needs is present: origin syntax, mutual exclusion of add/remove vs set, the required scope, error codes and what to do next, and a link to the guide. No notable gaps remain.

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 baseline is 3, but the description adds real meaning: add/remove are combinable ("add and / or remove"), set is mutually exclusive with them, and an origin is scheme+host with no path, illustrated by two examples. The only thing left unsaid is whether remove is a no-op for absent origins.

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?

Uses a specific verb ("Change") plus a precise resource ("the domains that may submit the site's forms") and names the underlying field (allowed_origins) and required scope (sites:write). An agent can distinguish this from update_settings or domains_add 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?

Gives an explicit trigger ("Use it when a form answers 403 origin_not_allowed") and names the alternative path for custom domains (domains_add handles them automatically while active), plus the escalation route when the free plan rejects a production domain (402 → plan_set). When-to-use, when-not-to-use, and alternatives are all covered.

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