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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), so the bar is lower. The description still adds non-annotation behavior: the operation costs nothing, the reference set is a fixed 186/117 enumeration, and filtering exists specifically to bound response size. What is missing is any statement about ordering or how the pairs are formatted in the payload.

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?

Three short sentences, all front-loaded: identity/scope first, then purpose, then the optional filter. The clipped 'Free.' fragment carries real selection information with almost no token cost, and there is no filler.

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 no output schema, the description carries the return-value burden and does reasonably well — it names the returned unit (location/language pairs) and the universe size. It stops short of describing how a caller should consume or match those values against the parameters of other tools, which would fully close the loop for a reference-data lookup.

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% and the schema already gives the substring-match semantics plus examples ('google.de', 'br', 'Deutsch'). The description's 'filter with a country domain, a code or a language name' restates those same three value classes, adding only the rationale that it keeps the answer short — marginal value, 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 ('Lists the supported Google versions') and immediately narrows what a version is: location/language pairs with concrete cardinality (186 domains, 117 languages). The stated purpose ('to pick valid location and language values') separates it cleanly from the data-fetching siblings like google_search and get_serp_results.

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?

Tells the agent the operative context: use it to obtain valid location/language values, and filter to keep responses short. 'Free' is a useful selection signal when weighed against paid siblings. It does not explicitly name an alternative tool or a when-not-to-use condition, so it falls short of 5.

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