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

Annotations already flag it as destructive and non-idempotent; the description adds genuinely useful behavior beyond them: 'set' zeroes other clicks in the segment, execution is asynchronous with a 'queued' result, and there is a 90-day editable window. It also discloses hidden carrier rules (bots skipped unless include_bots, landing-exit clicks never carry cost). It does not mention required permissions or permanence of the overwrite, so it stops short of 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?

Dense single paragraph with the core action front-loaded and mode/distribution semantics grouped in the middle. Every clause carries information, though the parenthetical-heavy style and the parenthetical example make it slower to parse than it needs to be.

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 60-parameter mutation tool with no output schema, the definition covers the essentials an agent needs: mode semantics, distribution behavior, async 'queued' result, and the 90-day window. It omits permission requirements and how to confirm completion, but nothing critical to correct invocation 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 88%, so the schema carries most of the load, but the description still adds meaning the schema lacks: why 'proportional' exists ('so an ad-network sync's shape survives and only the total moves') and the interaction of unique_only/include_bots with cost carriers. The 60 filter parameters are not described, which is reasonable but keeps it from a 5.

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 concrete verb and resource ('book a known spend onto a traffic SEGMENT — period + analytics filters') and disambiguates from the nearest sibling by noting it 'works like per-campaign cost booking, for arbitrary segments', implicitly contrasting with set_campaign_costs. An agent can identify the operation without opening the 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?

The example ('I spent $500 on offer 3 / zone 1234 last week, lay it out') gives a clear triggering scenario, and the closing sentence contrasts it with per-campaign cost booking. However, it never explicitly routes to or away from siblings like preview_segment_costs, set_campaign_costs, or import_meta_costs, so the alternative-selection step is left implied.

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