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

Annotations already cover readOnly/idempotent/non-destructive/closed-world, and the description adds genuinely new behavioral facts: deterministic processing with no AI inside and no logging. The response field list is somewhat redundant given an output schema exists, but the determinism and logging guarantees are real added value.

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 behavioral core (what converts, what stays untouched) is front-loaded in the first sentence, and the second carries guarantees and return shape. The inline list of response fields is a bit dense and largely duplicated by the output schema, slightly diluting efficiency.

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, read-only transformation with an output schema and full annotations, the description covers purpose, scope, determinism, and privacy. The only gap is the absence of explicit guidance on when to pick this over sibling normalization/formatting tools.

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 only 50% — the 'to' enum is documented in the schema but 'text' has an empty description. The description partially compensates by making clear that the entire text is scanned and non-digit characters are preserved, which is the key semantic an agent needs, but it adds nothing about the 'to' values beyond the schema's enum.

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?

States a specific verb (rewrite) and resource (digits) with the exact three numeral systems named, plus the scope qualifier 'anywhere in a text, leaving everything else untouched.' An agent can distinguish it from format_number or normalize_arabic by intent, though no sibling is named explicitly.

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?

Usage is implied by 'anywhere in a text,' which suggests whole-string conversion rather than formatting a single number, but there is no explicit when-to-use versus normalize_arabic, format_number, or transliterate, and no stated preconditions. The agent must infer the routing decision from sibling names alone.

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