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

Annotations already declare non-readonly, non-destructive, idempotent, and closed-world, so the safety profile is covered. The description adds behavior the annotations do not: the change is scoped to this user and also affects outbound emails, not just the app UI. That's meaningful side-effect disclosure for an agent reasoning about consequences.

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?

One compact sentence with the core scope stated first and the disambiguation trailing, so it's front-loaded correctly. The leading colon construction is slightly awkward, but nothing is wasted.

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 one enum-constrained parameter, full schema coverage, and annotations covering idempotency and safety, the description only needs to fix scope and side effects, which it does. A note on whether the user must be re-authenticated or what confirmation returns would close the remaining gap, but that's minor.

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% and the enum already documents en = English, it = Italian. The description repeats the 'en' or 'it' values without adding format, default, or fallback semantics. Baseline 3 is appropriate when the schema carries the parameter burden.

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 the specific resource and effect: it changes the app and email language for this user, with the allowed values en/it. It clearly separates this from video_language, so an agent won't conflate it with update_project. It stops short of using an explicit verb such as 'set', but the intent is unambiguous.

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 a real exclusion ('not the language of the videos') and points to the correct alternative for that need (update_project's video_language). What's missing is positive guidance on when to reach for this tool, e.g. after the user asks to change UI/email language, but the routing signal is strong.

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