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create_cart

Start the open UCP purchase flow, no auth needed. Creates a cart session and returns a cart_id (24-hour TTL). Optionally seed with pre-configured blind items and customer details. Next step: update_cart to add items, then create_checkout → complete_checkout to mint the payment link.

Input Schema

NameRequiredDescriptionDefault
itemsNoOptional configured items; all submitted prices are ignored
customerNoOptional customer details (name, email, phone, address, city).

Output Schema

NameRequiredDescriptionDefault
itemsYes
cart_idYes
currencyYes
customerYes
total_zarYes
created_atYes
expires_atYes
item_countYes
updated_atYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • addedInput schema / properties / customer / description
      Added value: +"Optional customer details (name, email, phone, address, city)."
  2. Changed5 schema fields changed
    • removedInput schema / properties / customer / description
      Removed value: -"Optional customer details"
    • addedInput schema / properties / customer / properties
      Added value: +{
      +  "address": {
      +    "type": "string"
      +  },
      +  "city": {
      +    "type": "string"
      +  },
      +  "email": {
      +    "description": "Real customer email, checked before checkout creation",
      +    "type": "string"
      +  },
      +  "name": {
      +    "description": "Real customer name, checked before checkout creation",
      +    "type": "string"
      +  },
      +  "phone": {
      +    "description": "South African phone number, checked before checkout creation",
      +    "type": "string"
      +  }
      +}
    • changedInput schema / properties / items / description
      Previous value: -"Optional initial items (configured blinds)"New value: +"Optional configured items; all submitted prices are ignored"
    • addedInput schema / properties / items / items
      Added value: +{
      +  "properties": {
      +    "colour": {
      +      "description": "Exact available colour; validate with configure_product before adding",
      +      "minLength": 1,
      +      "type": "string"
      +    },
      +    "finish": {
      +      "description": "Optional pricing finish for aluminium Venetians",
      +      "type": "string"
      +    },
      +    "height_mm": {
      +      "description": "Actual ordered drop in millimetres",
      +      "exclusiveMinimum": 0,
      +      "type": "number"
      +    },
      +    "mount_type": {
      +      "description": "Use inside for recess fit or outside for face fix",
      +      "minLength": 1,
      +      "type": "string"
      +    },
      +    "product_id": {
      +      "description": "product_id returned by search_catalog or lookup_catalog",
      +      "type": "string"
      +    },
      +    "product_name": {
      +      "description": "Optional; server resolves the catalogue name",
      +      "type": "string"
      +    },
      +    "quantity": {
      +      "description": "Number of blinds; defaults to 1",
      +      "type": "number"
      +    },
      +    "total_price_zar": {
      +      "description": "Optional, ignored: server recalculates all totals",
      +      "type": "number"
      +    },
      +    "unit_price_zar": {
      +      "description": "Optional, ignored: server recalculates all prices",
      +      "type": "number"
      +    },
      +    "width_mm": {
      +      "description": "Actual ordered width in millimetres",
      +      "exclusiveMinimum": 0,
      +      "type": "number"
      +    }
      +  },
      +  "required": [
      +    "product_id",
      +    "width_mm",
      +    "height_mm",
      +    "colour",
      +    "mount_type"
      +  ],
      +  "type": "object"
      +}
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
      +  "additionalProperties": true,
      +  "properties": {
      +    "cart_id": {
      +      "type": "string"
      +    },
      +    "created_at": {
      +      "type": "string"
      +    },
      +    "currency": {
      +      "const": "ZAR",
      +      "type": "string"
      +    },
      +    "customer": {
      +      "anyOf": [
      +        {
      +          "additionalProperties": true,
      +          "properties": {
      +            "address": {
      +              "anyOf": [
      +                {
      +                  "type": "string"
      +                },
      +                {
      +                  "type": "null"
      +                }
      +              ]
      +            },
      +            "city": {
      +              "anyOf": [
      +                {
      +                  "type": "string"
      +                },
      +                {
      +                  "type": "null"
      +                }
      +              ]
      +            },
      +            "email": {
      +              "type": "string"
      +            },
      +            "name": {
      +              "type": "string"
      +            },
      +            "phone": {
      +              "anyOf": [
      +                {
      +                  "type": "string"
      +                },
      +                {
      +                  "type": "null"
      +                }
      +              ]
      +            }
      +          },
      +          "required": [],
      +          "type": "object"
      +        },
      +        {
      +          "type": "null"
      +        }
      +      ]
      +    },
      +    "expires_at": {
      +      "type": "string"
      +    },
      +    "item_count": {
      +      "type": "number"
      +    },
      +    "items": {
      +      "items": {
      +        "additionalProperties": true,
      +        "properties": {
      +          "colour": {
      +            "type": "string"
      +          },
      +          "finish": {
      +            "anyOf": [
      +              {
      +                "type": "string"
      +              },
      +              {
      +                "type": "null"
      +              }
      +            ]
      +          },
      +          "height_mm": {
      +            "type": "number"
      +          },
      +          "mount_type": {
      +            "type": "string"
      +          },
      +          "product_id": {
      +            "type": "string"
      +          },
      +          "product_name": {
      +            "type": "string"
      +          },
      +          "quantity": {
      +            "type": "number"
      +          },
      +          "total_price_zar": {
      +            "type": "number"
      +          },
      +          "unit_price_zar": {
      +            "type": "number"
      +          },
      +          "width_mm": {
      +            "type": "number"
      +          }
      +        },
      +        "required": [
      +          "product_id",
      +          "width_mm",
      +          "height_mm",
      +          "quantity",
      +          "unit_price_zar",
      +          "total_price_zar"
      +        ],
      +        "type": "object"
      +      },
      +      "type": "array"
      +    },
      +    "total_zar": {
      +      "type": "number"
      +    },
      +    "updated_at": {
      +      "type": "string"
      +    }
      +  },
      +  "required": [
      +    "cart_id",
      +    "items",
      +    "item_count",
      +    "total_zar",
      +    "currency",
      +    "customer",
      +    "created_at",
      +    "updated_at",
      +    "expires_at"
      +  ],
      +  "type": "object"
      +}
  3. First observed

TDQS

A4.3/5.0
Behavior4/5

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

Annotations only say readOnlyHint=false and destructiveHint=false; the description adds genuinely new behavior: no auth is required, the returned cart_id expires after 24 hours, and seeding with items/customer details is optional. It does not cover failure modes (e.g., invalid colour or product_id) or whether a cart can be re-seeded, so it is good but not complete.

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?

Three short sentences: what it does, what it returns with its TTL, and the workflow it belongs to. The workflow pointer is last where it belongs, and no sentence is filler.

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

Completeness5/5

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

With an output schema present, return values are covered by structure, yet the description still surfaces the one thing an agent must know (cart_id and its 24-hour expiry) plus auth and workflow position. For a 2-param nested-object tool, that is sufficient to call it correctly.

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% and every nested field is documented, including the unusual 'prices are ignored, server recalculates' rule. The description only restates that items and customer details are optional seeds, adding little beyond the schema, so the baseline of 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?

States a concrete verb and resource ('Creates a cart session') plus the concrete return value ('cart_id (24-hour TTL)'), and frames it as the entry point of the purchase flow. An agent can distinguish it from siblings like get_cart or update_cart without opening any schema.

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?

Explicitly routes the agent forward ('Next step: update_cart to add items, then create_checkout → complete_checkout'), which is the key sequencing decision for this tool family. It does not state when not to use it (e.g., to resume an existing cart use get_cart), so it stops short of full alternative coverage.

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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