preflight

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

Annotations cover the safety profile (readOnlyHint=true, openWorldHint=false), but the description adds material behavior of its own: it performs no payment, contacts no data provider, checks budget/limits, and returns the normalized input. That cost and side-effect disclosure is exactly the context an agent needs before spending money.

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, front-loaded with 'FREE.' as the decisive fact, then the operation, then the return value, then the call-to-action. No sentence is redundant.

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 two-parameter validation tool with no output schema, the description covers cost, side effects, what is checked, and the return value. The one gap is failure behavior — it doesn't say whether an invalid input raises an error or returns a flag in the normalized result.

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%, with both `service` and `input` documented in the schema itself, so the baseline is 3. The description reinforces that `input` must mirror the paid tool's arguments ('Returns the normalized input') but adds no syntax or format detail beyond that.

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+resource: validates an input for a paid tool and checks budget/limits, and explicitly says it does so without paying or calling any data provider. That distinguishes it cleanly from the paid siblings like keyword_metrics or google_serp, which actually fetch data.

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?

'Use it before a paid call to avoid wasted payments' gives a clear trigger condition, and 'FREE' reinforces the cost rationale. It stops short of naming a specific sibling to pair with or stating when a preflight can be skipped, keeping it just below a 5.

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