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

Annotations already indicate a destructive, non-read-only operation, and the description adds meaningful behavioral context: it generates translations for missing keys and uses the default-locale value as the translation source. This reveals side effects beyond the raw annotation flags without contradicting them.

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?

Two tight sentences communicate the core action, the scope ('every key currently missing'), and the source behavior. There is no filler or redundancy.

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?

The description, combined with full schema coverage, annotations, and an output schema, is nearly complete. A brief note about prerequisites (e.g., the project must have a default locale) would make it fully comprehensive, but no essential calling behavior is missing.

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?

The input schema covers all four parameters with descriptions, so the baseline is 3. The description adds general context about translation sourcing but does not add per-parameter semantic detail beyond what the schema already provides.

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 clearly identifies the verb ('Add') and specific resource ('a new locale'), then expands on what the operation does: generate translations for all currently missing keys using the default-locale value as source. This distinguishes add_locale from siblings like add_project, add_phrase, and even find_missing_translations.

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?

The description makes the use context clear: add a locale and fill in missing translations. It does not explicitly name alternatives or state when not to use it, but the context is unambiguous enough for an agent to select it appropriately.

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