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

Annotations already declare destructiveHint=true, and the description adds useful behavioral detail: it only fills keys currently missing and uses the default-locale value as the source. This prevents an agent from assuming existing translations are overwritten. It doesn't enumerate every side effect, but for a creation/generation tool this is reasonably transparent.

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 sentences with no filler; the primary action and the translation-generation behavior are stated first, and the source-locale detail follows in the second sentence. Every sentence earns its place.

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 a complete schema and output schema, provides enough for an agent to select and call the tool. A minor gap is lack of guidance on what happens if the locale already exists, but 'add a new locale' covers the main expectation.

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 baseline is 3. The description adds the meaning of 'default-locale' as source and clarifies 'missing translations', but does not explain model or context parameters beyond what the schema already states.

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 ('Add'), a resource ('a new locale to a project'), and a concrete action ('generate translations for every key currently missing'). It clearly distinguishes this from siblings like add_project and 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 intended use case clear: use this tool when adding a new locale and populating it with translations for missing keys. It does not explicitly name alternatives or exclusions, but the scenario is specific enough for an agent to choose correctly.

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