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

Annotations already establish the safe read-only, idempotent, non-destructive profile, so the bar is lower. The description adds real behavioral value beyond that: it always returns both entries, enumerates the reported states, explains the `supported` flag, and discloses the 409 variants_unavailable behavior and the M365 integration dependency. It stops short of describing pagination or ordering, if any.

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 tightly focused sentences, front-loaded with the core action and backed by the variant definition and the `supported` caveat. Every sentence earns its place, though the variant definition is slightly expansive for a list tool.

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 an output schema present, return fields needn't be re-explained, yet the description still clarifies `supported` and the 409 edge case. Combined with 100% param coverage and full annotations, an agent has everything needed to call it correctly; only explicit sibling routing is absent.

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 both parameters (signature_id and the analytics-only context field) are already fully documented. The description adds no parameter-level detail beyond the schema, so the baseline 3 applies.

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 gives a specific verb (List) and a precisely scoped resource (a signature's reply and internal variants), then defines what a 'variant' is and its two sub-types. The resource is specific enough that an agent can distinguish it from siblings like list_signatures or get_signature_html without opening the 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?

It provides a useful prerequisite (variants require an active Microsoft 365 signatures integration) and the failure condition (writes return 409 variants_unavailable when unsupported), which is implied usage context. However, it never explicitly says when to call this versus update_signature_variant, delete_signature_variant, or preview_signature, leaving routing to inference.

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