Explain a filter decision

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

Annotations already signal readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful behavioral context: the tool produces a verdict and names the exact filtering rule, and it frames the underlying problem of silent drops being indistinguishable from messages that never arrived.

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?

The description is extremely compact: one direct statement of purpose followed by one sentence of motivating rationale. Every sentence earns its place, and the core behavior is front-loaded.

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?

Given the tool's low complexity, two parameters, existing output schema, and read-only annotations, the description is mostly sufficient. The main gap is the lack of parameter-level explanation, but the purpose, behavior, and rationale are adequately covered for an agent to select and invoke the tool.

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 0%, and the description does not explain what 'uid' or 'mailbox' mean beyond saying 'one message.' The meaning of uid is left mostly to inference from the parameter name. With no schema descriptions, the description should compensate more fully for parameter semantics.

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 states the exact purpose: 'Say whether one message would be ingested, and why.' It identifies the resource (a single message) and the output (ingestion decision plus the rule responsible). The 'smart-default filter auditable' framing distinguishes it from sibling tools like imap_read_message or imap_search_messages.

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?

The description gives clear context for when to use the tool: to audit the smart-default filter when a message silently fails to reach the vault, and to identify the exact rule that dropped it. It does not explicitly name alternative tools or state when not to use it, but the diagnostic niche is clear enough.

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