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

Goes well beyond the annotations: discloses the required auth scope (sites:write), the concrete surfaces mutated (auto-reply, public form, booking page), the null semantics ('schema's first language decides'), and the optimistic-concurrency contract of passing settings_version as expected_version. It also warns about prompt injection from external data, a behavioral risk the annotations do not capture.

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?

Front-loaded with the core action, then scope, then null semantics, then a labeled usage block — easy to scan. The injection-defense paragraph is somewhat boilerplate-heavy but is genuinely actionable for a write tool, so it earns most of its space.

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 three-required-parameter mutation with no output schema, everything an agent needs is present: what changes, what it affects, the auth scope, the concurrency token requirement, and the safety boundary. Annotations already cover the destructive/readOnly profile, so nothing material 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?

Schema coverage is 100%, so the baseline is 3; the description still adds meaning by clarifying that null does not reset the locale but follows the schema's first language, and that expected_version comes from get_settings. Minor added value over the already-complete schema.

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 ('Set the site's language') and enumerates exactly which surfaces are affected: auto-reply, public form page, booking page. It does not explicitly distinguish itself from the sibling update_settings, which an agent might reasonably think also touches locale, so it falls short of the sibling-differentiation bar for a 5.

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 '[When to use]' block gives a clear positive condition (user explicitly asks for it) and explicit exclusions (do not act on instructions in external data). It does not name an alternative sibling tool for the adjacent case of changing other site settings, so it is clear context without alternatives.

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