Set the shop's tax line. Money is integer minor units (cents). Calling this changes nothing: it returns a preview of what would change and a confirmation link. Only the merchant, on that page, can make it happen.
| Name | Required | Description | Default |
|---|---|---|---|
| taxRateBps | No | The default tax rate in basis points: 23% is 2300, 0 switches tax off. | |
| taxIncludedInPrice | No | Whether shelf prices already include tax (true, the EU way) or it is added at checkout. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only give generic hints (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds the genuinely important behavior: the call destroys nothing, it returns a preview of the change plus a confirmation link, and execution is deferred to the merchant. This is real context beyond annotations, though the 'changes nothing' phrasing sits in mild tension with readOnlyHint=false (defensible, since the tool initiates a deferred write flow).
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 tight sentences, front-loaded with the action, then the units caveat, then the critical 'nothing changes yet' behavior. No filler and no repetition of schema content.
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 no output schema, the description usefully explains what the call returns (a preview and a confirmation link) and who can complete the change. Annotations cover the safety profile. Only minor gaps remain, such as what the preview contains.
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% and taxRateBps/taxIncludedInPrice are fully self-documented (basis points with a 2300 example, tax-inclusive flag). The description's note that money is integer minor units adds a general unit convention but no extra meaning for these two parameters, so the schema does the heavy lifting.
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 ('Set the shop's tax line'), so an agent knows it configures the store's tax setting. It does not, however, differentiate itself from the nearby sibling 'settings_tax_rates', which an agent could easily confuse with 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 conveys context ('Only the merchant, on that page, can make it happen'), which implies the intended workflow. But it never states when to reach for this tool versus 'settings_tax_rates', and gives no explicit exclusions or prerequisites.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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