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

Annotations already declare readOnlyHint=false and destructiveHint=true. The 'Side effects: modifies contact group' line reinforces that in plain language but adds little nuance beyond what annotations provide, such as partial-update behavior or effects on contacts assigned to the tag. It does not contradict the annotations.

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 very short and front-loaded with the core purpose. The side-effects line is somewhat redundant with the annotations but remains concise and non-wasteful.

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?

The basic purpose, parameters, and safety profile are covered, and an output schema exists. However, the tool lacks explicit guidance on partial-update semantics (e.g., whether omitting name clears it) and on how it differs from set-contact-groups, leaving some ambiguity for correct invocation.

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 the schema already documents group_id and the payload object with its name and notes properties. The description adds no parameter-level detail, but none is needed given the schema's coverage.

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 a specific verb ('Update') and resource ('contact group'), and clarifies that the resource is a Fax.Plus tag. This distinguishes it from update-contact and related tools, though it mostly mirrors the tool name and title.

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 guidance on when to use this tool instead of alternatives like create-contact-group, set-contact-groups, or update-contact. An agent has to infer the use case from the resource name alone.

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