mcp-gateway

create_cart

Idempotent

Create a shopping cart in Demo Store. Returns a cart_id for use with get_shipping_rates, preview_checkout, and complete_checkout.

SKYFIRE TOKEN (optional): Provide a kya or kya-pay Skyfire token in the skyfire-pay-id request header to boost your agent trust score (up to +0.35), which may unlock better pricing or priority service. No token required — request proceeds with neutral trust score (0.50) if omitted or invalid. PAYMENT MANDATE: this tool also requires one, sent as an X-Payment-Mandate header. This tool does not accept extra arguments, so the header is the only channel here. It must carry mandate_id, max_amount_cents, currency, exp, sub, aud, and its currency must match the cart's currency or the call is denied outright. The cap in max_amount_cents is enforced against the cart total. CREDENTIAL: this store needs one. Call the create_sandbox_key tool first (it is in this tool list and needs no credential), then pass the key you get back as the agent_key argument — or as an Authorization: Bearer header if your client can set headers. Do not ask a person to log in: there is no human login for this store.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`items`	Yes	Items to add to cart
`agent_token`	No	JWS compact (EdDSA/Ed25519) signed by the agent. Required for Shopify enforcement rules R001/R002/R004. The token is embedded as a server-authoritative cart attribute — Trusteed does NOT verify the signature here; that is done offline by the Shopify Function WASM.
`display_context`	No	Agent display capability: webview (browser) or headless	headless
`agent_session_id`	No	Opaque agent session identifier for cart resume across sessions

Output Schema

TableJSON Schema

Name	Required	Description	Default
`items`	Yes
`status`	Yes
`cart_id`	Yes
`currency`	Yes
`store_name`	Yes
`session_state`	Yes
`subtotal_cents`	Yes
`display_context`	Yes
`agent_session_id`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedSep 17, 2026
- changedOutput schema / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / items / items / additionalProperties
```
Previous value: -falseNew value: +true
```
Changed4 schema fields changedSep 11, 2026
- changedInput schema / properties / items / items / properties / variant_id / description
```
Previous value: -"Variant ID (optional)"New value: +"Variant ID (optional). Must match a variant id listed by get_product_details; an unknown id is rejected rather than silently replaced by the default variant."
```
- addedOutput schema / properties / items / items / properties / sku
```
Added value: +{
+  "type": "string"
+}
```
- addedOutput schema / properties / items / items / properties / variant_id
```
Added value: +{
+  "type": "string"
+}
```
- addedOutput schema / properties / items / items / properties / variant_title
```
Added value: +{
+  "type": "string"
+}
```

Changed1 schema field changedSep 8, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "agent_session_id": {
+      "type": "string"
+    },
+    "cart_id": {
+      "type": "string"
+    },
+    "currency": {
+      "type": "string"
+    },
+    "display_context": {
+      "enum": [
+        "webview",
+        "headless"
+      ],
+      "type": "string"
+    },
+    "items": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "line_price": {
+            "type": "number"
+          },
+          "name": {
+            "type": "string"
+          },
+          "quantity": {
+            "type": "number"
+          },
+          "unit_price": {
+            "type": "number"
+          }
+        },
+        "required": [
+          "name",
+          "quantity",
+          "unit_price",
+          "line_price"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "session_state": {
+      "enum": [
+        "new",
+        "resumed"
+      ],
+      "type": "string"
+    },
+    "status": {
+      "const": "NOT_READY_FOR_PAYMENT",
+      "type": "string"
+    },
+    "store_name": {
+      "type": "string"
+    },
+    "subtotal_cents": {
+      "type": "number"
+    }
+  },
+  "required": [
+    "cart_id",
+    "store_name",
+    "items",
+    "subtotal_cents",
+    "currency",
+    "status",
+    "agent_session_id",
+    "session_state",
+    "display_context"
+  ],
+  "type": "object"
+}

Changed4 schema fields changedAug 24, 2026

addedInput schema / $schema

Added value: +"http://json-schema.org/draft-07/schema#"

addedInput schema / additionalProperties
```
Added value: +false
```

addedInput schema / properties

Added value: +{
+  "agent_session_id": {
+    "description": "Opaque agent session identifier for cart resume across sessions",
+    "type": "string"
+  },
+  "agent_token": {
+    "description": "JWS compact (EdDSA/Ed25519) signed by the agent. Required for Shopify enforcement rules R001/R002/R004. The token is embedded as a server-authoritative cart attribute — Trusteed does NOT verify the signature here; that is done offline by the Shopify Function WASM.",
+    "type": "string"
+  },
+  "display_context": {
+    "default": "headless",
+    "description": "Agent display capability: webview (browser) or headless",
+    "enum": [
+      "webview",
+      "headless"
+    ],
+    "type": "string"
+  },
+  "items": {
+    "description": "Items to add to cart",
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "product_id": {
+          "description": "Product ID",
+          "type": "string"
+        },
+        "quantity": {
+          "default": 1,
+          "description": "Quantity",
+          "minimum": 1,
+          "type": "integer"
+        },
+        "variant_id": {
+          "description": "Variant ID (optional)",
+          "type": "string"
+        }
+      },
+      "required": [
+        "product_id"
+      ],
+      "type": "object"
+    },
+    "minItems": 1,
+    "type": "array"
+  }
+}

addedInput schema / required
```
Added value: +[
+  "items"
+]
```

Changed5 schema fields changedJul 10, 2026

removedInput schema / $schema

Removed value: -"http://json-schema.org/draft-07/schema#"

removedInput schema / additionalProperties
```
Removed value: -false
```

removedInput schema / properties

Removed value: -{
-  "agent_session_id": {
-    "description": "Opaque agent session identifier for cart resume across sessions",
-    "type": "string"
-  },
-  "display_context": {
-    "default": "headless",
-    "description": "Agent display capability: webview (browser) or headless",
-    "enum": [
-      "webview",
-      "headless"
-    ],
-    "type": "string"
-  },
-  "items": {
-    "description": "Items to add to cart",
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "product_id": {
-          "description": "Product ID",
-          "type": "string"
-        },
-        "quantity": {
-          "default": 1,
-          "description": "Quantity",
-          "minimum": 1,
-          "type": "integer"
-        },
-        "variant_id": {
-          "description": "Variant ID (optional)",
-          "type": "string"
-        }
-      },
-      "required": [
-        "product_id"
-      ],
-      "type": "object"
-    },
-    "minItems": 1,
-    "type": "array"
-  }
-}

removedInput schema / required
```
Removed value: -[
-  "items"
-]
```

changedOutput schema / (root)

Previous value: -{
-  "$schema": "http://json-schema.org/draft-07/schema#",
-  "additionalProperties": false,
-  "properties": {
-    "agent_session_id": {
-      "type": "string"
-    },
-    "cart_id": {
-      "type": "string"
-    },
-    "currency": {
-      "type": "string"
-    },
-    "display_context": {
-      "enum": [
-        "webview",
-        "headless"
-      ],
-      "type": "string"
-    },
-    "items": {
-      "items": {
-        "additionalProperties": false,
-        "properties": {
-          "line_price": {
-            "type": "number"
-          },
-          "name": {
-            "type": "string"
-          },
-          "quantity": {
-            "type": "number"
-          },
-          "unit_price": {
-            "type": "number"
-          }
-        },
-        "required": [
-          "name",
-          "quantity",
-          "unit_price",
-          "line_price"
-        ],
-        "type": "object"
-      },
-      "type": "array"
-    },
-    "session_state": {
-      "enum": [
-        "new",
-        "resumed"
-      ],
-      "type": "string"
-    },
-    "status": {
-      "const": "NOT_READY_FOR_PAYMENT",
-      "type": "string"
-    },
-    "store_name": {
-      "type": "string"
-    },
-    "subtotal_cents": {
-      "type": "number"
-    }
-  },
-  "required": [
-    "cart_id",
-    "store_name",
-    "items",
-    "subtotal_cents",
-    "currency",
-    "status",
-    "agent_session_id",
-    "session_state",
-    "display_context"
-  ],
-  "type": "object"
-}New value: +null

First observedApr 28, 2026

TDQS

A4.1/5.0

Behavior5/5

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

Goes well beyond the annotations by disclosing required payment-mandate headers (and their currency-match denial rule), optional Skyfire trust-token effects, credential requirements, and the absence of human login. It also warns that invalid tokens proceed with a neutral trust score and that the max_amount cap is enforced.

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

Conciseness4/5

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

The description is long, but the SKYFIRE TOKEN / PAYMENT MANDATE / CREDENTIAL labels make it scannable, and the core purpose is front-loaded. Nearly every sentence carries operational information; only the incorrect `agent_key` reference keeps it from being fully reliable and tidy.

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

Completeness3/5

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

For a state-changing tool with auth and mandate requirements, it covers a great deal: prerequisites, headers, trust-score effects, and downstream usage. However, the central credential-preservation step is inaccurate (`agent_key` vs the schema's actual parameters), and it never explains how the agent determines the cart's currency to satisfy the mandate's currency-match rule.

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

Parameters2/5

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

The schema has 100% description coverage, so baseline would be 3, but the description introduces an `agent_key` argument that does not exist in the input schema, which has additionalProperties: false. An agent following this instruction would submit an invalid tool call; the description does not map the create_sandbox_key output to the actual `agent_token`, `display_context`, or `agent_session_id` parameters.

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?

Opens with a specific verb and resource: 'Create a shopping cart in Demo Store,' and distinguishes itself from checkout/shipping siblings by stating it returns a cart_id for use with get_shipping_rates, preview_checkout, and complete_checkout. This is unambiguous and separates it from create_sandbox_key and the ucp_* checkout tools.

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?

Provides explicit execution context: call create_sandbox_key first, pass the returned credential (or Bearer header), and do not attempt human login. It also places the tool in a sequence with get_shipping_rates, preview_checkout, and complete_checkout. It stops short of naming alternate cart/checkout tools or exclusion conditions, so it is strong but not a full when/when-not guide.

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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