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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; beyond that the description discloses the empty-result semantics and, importantly, that failures arrive as a single-element list containing an 'error' key (api_error/task_error, dfs_timeout, dfs_unreachable) which must be checked before evaluation. That error-channel warning is genuinely non-obvious behavior an agent would otherwise mishandle.

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?

The opening sentence front-loads what is returned and the parenthetical enumerates the fields compactly; the empty-list rule, parameter defaults and error contract follow in tight parenthetical clauses. It is dense but nearly every clause carries operational information, with only the field enumeration overlapping the output schema.

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 four-parameter read tool with an output schema, an agent has what it needs: scope, snapshot limitation, empty-result meaning, sibling alternative, parameter defaults and the error shape to check for. The only shortfall is the deferred location/language format reference, which leaves a small ambiguity unresolved within this definition.

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 0%, so the description must carry the parameters, and it does cover most of them: location and language fall back to the workspace default and follow the dfs_keyword_volume format, while workspace is a customer slug that becomes optional when only one workspace exists. The compensation is decent but not complete — the 'format as in dfs_keyword_volume' pointer defers the actual format to another tool rather than stating it.

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 states a specific verb and resource: it returns the paid ads currently showing on a keyword in the Google SERP, and explicitly frames the result as a desktop snapshot (titles, descriptions, target URLs, positions, sitelinks). It also pre-empts a likely confusion by naming the sibling dfs_google_ads_advertisers for the different question of who advertises on the topic at all.

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?

It explicitly says an empty list means no ads were served for this particular fetch, and routes the agent to dfs_google_ads_advertisers when the question is about general topic advertisers — a clear when-to-use-this-vs-that rule. The one gap is that it never contrasts itself with the organic SERP sibling (dfs_serp_google_organic), which an agent could plausibly reach for instead.

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