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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral context: per-locale cap of 24 locales, 2,000 characters each, machine-translation flags, and that it renders a phrase card. It does not discuss errors when a key is absent, which keeps it from a 5.

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 tightly packed sentences with zero filler; the usage trigger and the sibling exclusion are front-loaded, and the limits and rendered output are packed into the same second sentence.

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 an output schema present, return values need not be spelled out, yet the description still usefully sketches them (per-locale text, MT flags, sharing projects, phrase card). Combined with annotations covering safety and 100% schema coverage, an agent has everything needed to call this correctly.

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 100%, so all three parameters are already documented including the case-sensitive exact match and the 'every language when absent' default. The description mirrors this at a summary level ('one exact key', 'every language or in one') without adding new semantics, so the baseline 3 applies.

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 and resource ('how one exact key is translated, in every language or in one') and explicitly distinguishes itself from search_phrases with 'Not for searching keys by text.' An agent can route between get_phrase and search_phrases without opening either schema.

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?

Gives an explicit trigger ('Use this when someone asks how one exact key is translated'), a scope condition (every language vs one), and an exclusion ('Not for searching keys by text') that names the competing sibling capability.

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