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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the bar is lower, but the description adds valuable context: it states the operation order (percentage, flat, rounding), provides a concrete example with expected output, and explains error handling (returns error objects instead of protocol errors). This exceeds the annotation coverage and fully discloses behavior.

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 description is compact yet information-dense, front-loading the purpose and the critical ordering note. Every sentence earns its place: purpose, example, usage guidance, alternative tool, error behavior, safety notes. No filler, well-structured for quick consumption by an agent.

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?

Given the tool's moderate complexity (5 params, one required) and the fact that an output schema and annotations exist, the description provides all necessary context: usage timing, parameter interactions, error handling, and safety profile. The example return object covers output expectations, making it complete.

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 100%, so baseline is 3. The description adds crucial semantics beyond the schema by explaining the exact order of application (percentage -> flat -> rounding -> charm ending) and clarifies the meaning of each parameter with a typical input example. It doesn't repeat schema details but enhances understanding, justifying a 4.

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 clearly states the tool applies a pricing rule across a list of prices and shows the effect, which is a specific verb+resource. It distinguishes itself from siblings like payout_estimate by explicitly contrasting its purpose, so the agent knows exactly when to use it.

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 explicitly says 'Use when repricing a catalogue before export' and explicitly notes 'Not for what a price nets you after Shopify's fees — that is payout_estimate,' naming an alternative tool. This meets the highest bar for usage guidance.

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