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

Annotations already signal destructive=true, and the description adds the critical detail that previous group assignments for the selected contacts are overwritten. It also discloses automatic group-ID-to-name resolution and a side-effects line, which are not present in the annotations or schema.

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 short and front-loaded with the purpose, then parameter guidance, then side effects. The explicit 'Side effects' line is slightly redundant with the overwrite sentence, but it does not add meaningful bloat.

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 3-parameter mutation tool with annotations and an output schema, the description covers purpose, parameter semantics, and side effects. It does not discuss prerequisites such as whether the named groups must already exist or the behavior of the shared flag, though the schema does cover the shared flag.

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 coverage is 100%, so the baseline is 3, but the description adds valuable semantic guidance beyond the schema: group names come from create-contact-group as IDs and must be converted, and a mistaken ID is auto-resolved to a name. This extra handling of the groups parameter justifies a 4.

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 opens with a specific verb and resource ('Assign contacts to contact groups') and clarifies the domain ('Fax.Plus tags'). It also distinguishes itself from create-contact-group by explicitly saying group names, not group IDs from that tool, which prevents a common mix-up.

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 gives clear operational context: pass names rather than IDs, and be aware that this tool replaces prior assignments. It does not explicitly state when to prefer this tool over close siblings such as share-contact-groups or update-contact, so it misses the exclusion guidance needed for a 5.

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