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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds real specifics beyond that: conditions are replaced wholesale rather than merged, and invalid input fails with 422. Those details materially change how an agent should prepare the call. It does not cover rate limits or auth scoping, keeping it off a 5.

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 tight sentences with zero filler. The core capability and the at-least-one precondition are front-loaded, followed by the replacement semantics and the error behavior, in order of decision-relevance.

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?

An output schema exists, so return values need no explanation, and annotations cover the safety profile. The description supplies the destructive-replacement nuance and the 422 failure mode, which are the main things an agent needs before calling. Only the absence of guidance on sourcing smart_field_id constraints (beyond the schema reference) keeps this from a 5.

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 every parameter (including the nested condition shape and the context field) is already documented in the schema. The description names the two meaningful inputs but adds no format or syntax detail beyond what the schema provides. Baseline 3 is correct when the schema does the heavy lifting.

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 (Set) plus the resource (a signature's rule-based targeting) and enumerates exactly what is set: the `conditions` tree and/or the `assign_to_all_future_emails` flag. It also carves out what it does not touch (manual and org-unit targeting), which cleanly separates it from sibling tools like add_signature_recipients.

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 tells the caller a precondition: provide at least one of conditions or assign_to_all_future_emails. The note that manual and org-unit targeting are untouched implies other tools handle those cases, but no sibling is named outright, so it falls short of a full when/when-not routing statement.

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