Amber's Slime Studio

Check a promo code

check_promo

Read-onlyIdempotent

Check whether a promo code applies to a basket of slimes (by slug and quantity) and estimate the saving. A rejected code returns valid=false with the shop's standard message; checkout always re-checks codes.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "code": "<code>",
      "items": "<items>"
    },
    "name": "check_promo"
  }
}

Input Schema

Name	Required	Description	Default
`code`	Yes	Promo code exactly as the shopper has it, e.g. 'WELCOME10'
`items`	Yes	The slimes the code would apply to; codes can depend on the basket

Output Schema

Name	Required	Description
`code`	Yes
`valid`	Yes
`message`	Yes
`subtotal_gbp`	Yes	Slimes subtotal before the discount in pounds sterling (GBP), e.g. 8.99
`discount_type`	Yes
`subtotal_pence`	Yes	Slimes subtotal before the discount in pence (GBP minor units), e.g. 899
`discount_summary`	Yes
`promo_description`	Yes
`estimated_discount_gbp`	Yes	Estimated saving on the subtotal in GBP; checkout confirms it
`estimated_discount_pence`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 10, 2026

TDQS

A4/5.0

Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered structurally. The description adds real value by disclosing the rejection contract (valid=false plus the shop's standard message) and the non-authoritative nature of the estimate, but it says nothing about lookup cost, code expiry handling, or stacking behavior for multiple codes.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the purpose, then the failure contract and the caveat about checkout re-validation. Nothing is redundant and each clause carries distinct information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, return-value detail is not the description's burden, and the description correctly focuses on the estimate-vs-authoritative distinction. The remaining gap is minor: it does not say whether the saving is returned as an absolute amount or a percentage, which an agent might want before presenting results.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters and their nested fields (code, slug, qty) are already documented in structured form, including the basket-dependency of codes. The description only restates that items are consumed as slug+quantity and adds no format, normalization, or case-sensitivity detail beyond the schema; baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Check whether a promo code applies to a basket of slimes (by slug and quantity) and estimate the saving.' No sibling tool (create_basket_link, get_product, search_catalog, etc.) overlaps with promo-code validation, and the parenthetical scope tells an agent exactly what inputs define the check.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It establishes the tool's role clearly by saying the result is an estimate and that 'checkout always re-checks codes', which steers an agent away from treating this as an authoritative final price. It stops short of naming a concrete alternative or a strict when-not condition, so it is strong context rather than complete routing guidance.

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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