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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds real behavioral context beyond that: the side effect is confined to the account and does not propagate to any contact, and dry_run provides a preview path. It does not disclose what happens on a duplicate name (relevant given idempotentHint=false) or what the response contains, which keeps it short of 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 short sentences, no filler, with the core action and the not-applied-to-contacts scope stated first. The dry_run hint comes last where a follow-up detail belongs.

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 two-parameter creation tool with full annotation coverage and no output schema, the description covers action, scope, required input, and safe-preview guidance — enough to invoke it correctly. The remaining gap is failure/duplicate behavior, which matters because idempotentHint is false but is not described.

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 are already documented in structured data, and the baseline of 3 applies. The description reinforces that name is required and recommends the dry_run preview, but adds no format, length, or uniqueness constraints for the tag name that the schema lacks.

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 and resource ("Create a new tag") plus its purpose ("for organizing contacts"), and then draws the key scope line: "Adds the tag to the account only; it is not applied to any contact." That last clause separates it from tag-application siblings such as remove_tag_from_contact and from update_tag/delete_tag, so an agent can route correctly without opening a 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 states a concrete precondition ("Needs a name") and a recommended workflow ("set dry_run: true to check first"), which tells the agent how to call this safely. It stops short of naming alternatives — e.g. when to use update_tag for an existing tag, or what to do if the tag already exists — so it is clear context without exclusions.

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