Configure a domain's catch-all email behavior by forwarding unrouted messages to a specified address or bouncing them with ':fail:'.
Configure the catch-all (default) email behavior for unrouted emails sent to a domain
| Name | Required | Description | Default |
|---|---|---|---|
| domain | Yes | Domain name (e.g. example.com) | |
| forward_to | Yes | Destination email address to forward unrouted mail to, or ':fail:' to bounce |
Changes observed during successful MCP inspections.
v2.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are supplied, so the description carries the full disclosure burden. It does not state that this is a mutating operation that overwrites the existing catch-all setting, whether existing forwarders are affected, what permissions/ownership are required, or whether the change is reversible. The one behavioral nuance that matters most (':fail:' to bounce) lives only in the schema, not the description.
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?
A single front-loaded sentence with no filler; the resource and scope come first. It is efficient but a bit thin for a mutating tool, so it sits just below the top band.
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 two-parameter write operation with zero annotation coverage and no output schema, the description should disclose side effects, required permissions, and expected outcome. It covers only the abstract purpose, leaving the agent without the behavioral context needed to invoke it confidently.
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% and both parameters are documented there, including the ':fail:' sentinel value, so the baseline is 3. The description adds no syntax, format, or constraints beyond what the schema already provides.
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?
The description names a specific resource and action: configuring catch-all (default) email handling for unrouted mail on a domain. The 'set' vs. sibling 'get_default_address' contrast is inferable from the verb, though the description never names that sibling explicitly.
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?
There is no when-to-use guidance, no prerequisites (e.g., domain must exist or be owned by the account), and no pointer to get_default_address for reading the current value before changing it. The agent must infer the entire usage context from the one-line purpose statement.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.