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

Goes well beyond the annotations: it discloses the overwrite semantics ('a day is set, not incremented'), the all-or-nothing requirement to include every row of a campaign for the covered days, rate-based currency conversion with the bad_currency code, and that unmatched campaigns are reported back. That is exactly the extra context destructiveHint=true does not convey. Minor tension: a set-not-increment operation reads as repeat-safe, which sits awkwardly with idempotentHint=false, though this is not a clear contradiction.

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?

One front-loaded paragraph that leads with the action, then the payload shape, then matching, then currency and overwrite rules. Dense but every clause carries operational meaning; only the parenthetical clarifications could be trimmed slightly.

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 destructive importer with no output schema, it covers input preparation, matching rules, currency handling, overwrite semantics and error reporting sufficiently to call it correctly. The remaining gap is return-shape detail — 'unmatched ones are reported back' is not specified in structure, and the row-limit failure mode is unaddressed.

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 75%, so the baseline is 3; the description earns above that by explaining what the key identifiers actually do at match time — campaign_id is resolved via the {campaignid} ValueTrack parameter carried on clicks, campaign_name enables the '(TID: N)' fallback, and a campaign feeding multiple tracker campaigns is split by click share. It does not mention the 5000-row maxItems cap or what a partial/oversized payload does.

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?

Opens with a specific verb and resource: 'Book Google Ads daily spend into click costs', and immediately scopes the payload to one row per day × Google campaign × ad group. An agent can distinguish it from import_meta_costs and set_campaign_costs, though the text never names those siblings explicitly.

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?

Usage is implied rather than stated: it is the tool to call when you have Google Ads Script spend rows, and the '(TID: N)' fallback plus the {campaignid} matching explain how to prepare them. There is no explicit when-to-use-this-instead-of-new() guidance against the competing cost tools (import_meta_costs, set_campaign_costs, preview_segment_costs), and no stated prerequisites such as account connectivity.

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