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

Annotations already carry readOnlyHint/idempotentHint, so 'READ-ONLY' adds little, but the description usefully defines the projected behavior (month-end spend projection), the meaning of the over/under flags, and the pace_pct formula. It stops short of stating time-range or account-scope constraints beyond customer_id.

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-loads the tool identity in caps, then the computation, then the flag semantics, then the parameter note. Dense and largely waste-free, though the em-dash fragments and trailing parameter/formula notes read as terse rather than cleanly structured.

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 an output schema present, the description need not enumerate return fields, and it still explains what the flags mean and how pace_pct is derived. What is missing is scope/permission context (which ad platforms, what customer_id refers to) and any indication of result volume.

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% with 2 parameters, so the description must compensate. It defines threshold_pct as the deviation threshold in percent (consistent with the schema default of 20), but customer_id is never explained and pace_pct is an output field, not an input.

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: projects this month's spend against daily budget and flags over/under-spending campaigns. That is clearly distinct from write siblings like set_campaign_budget or reporting siblings like performance_report, though no sibling is named 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?

The description explains what the tool computes but gives no when-to-use guidance, no prerequisites (e.g. account must be connected), and no routing away from alternatives such as performance_report or get_report. Usage is only inferable from the purpose sentence.

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