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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds that the tool normalizes rather than merely checks, and that it returns operator information — useful context beyond annotations — but it does not say what happens with invalid input or what the response shape looks like.

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 operation front-loaded and the secondary operator-detection fact appended. Nothing is wasted, though the sentence is terse enough that it omits necessary detail rather than being optimally structured.

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 one-parameter, annotation-rich, idempotent read tool this is close to adequate: the operation and its second output are stated. The missing piece is input-format expectations, which matters more than usual given the 0% schema coverage and the absence of an output schema.

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 0%, so the description must carry the meaning of the single `telepon` parameter, and it does not. It never states whether the expected input is 08xx, +62, or 62-prefixed, nor whether separators or spaces are tolerated, leaving the only parameter undocumented.

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 names a specific verb+resource ("Normalize Indonesian phone number") plus a secondary capability ("detect mobile operator"), so an agent can tell it apart from generate_dummy_phone. It does not name siblings explicitly, and it slightly diverges from the name/title ("validate" / "check format" vs "normalize"), but the intent is still clear.

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?

No guidance on when to use this versus the nearby validate_nik, validate_npwp, validate_bank_account, or generate_dummy_phone tools. It also never says what input forms are acceptable, which is exactly the decision an agent must make before calling.

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