mcp-gateway

ucp_update_checkout

Idempotent

Update a UCP checkout session by fully replacing all line items. Only allowed when status is 'incomplete'. PAYMENT MANDATE: this tool also requires one. Send it as the payment_mandate argument if your client cannot set headers, or as an X-Payment-Mandate header. 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.

Input Schema

TableJSON Schema

Name	Required	Description
`currency`	Yes	ISO 4217 currency code (e.g. USD)
`line_items`	Yes	Replacement line items
`checkout_id`	Yes	UCP checkout session ID (valid UUID)
`payment_mandate`	No	Payment mandate with `mandate_id`, `max_amount_cents`, `currency`, `exp`, `sub`, `aud`. Its `currency` must match the cart's. Use this when your client cannot set an `X-Payment-Mandate` header.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`id`	Yes
`label`	No
`intent`	No
`status`	Yes
`totals`	Yes
`currency`	Yes
`created_at`	Yes
`extensions`	No
`line_items`	Yes
`updated_at`	Yes
`idempotency_key`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026

addedInput schema / properties / payment_mandate

Added value: +{
+  "anyOf": [
+    {
+      "additionalProperties": {},
+      "type": "object"
+    },
+    {
+      "type": "string"
+    }
+  ],
+  "description": "Payment mandate with `mandate_id`, `max_amount_cents`, `currency`, `exp`, `sub`, `aud`. Its `currency` must match the cart's. Use this when your client cannot set an `X-Payment-Mandate` header."
+}

Changed9 schema fields changedSep 17, 2026
- changedInput schema / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedInput schema / properties / line_items / items / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / extensions / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / extensions / properties / warnings / items / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / intent / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / line_items / items / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / line_items / items / properties / price / additionalProperties
```
Previous value: -falseNew value: +true
```
- changedOutput schema / properties / totals / items / additionalProperties
```
Previous value: -falseNew value: +true
```
AddedSep 9, 2026
RemovedSep 1, 2026

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: +{
+  "checkout_id": {
+    "description": "UCP checkout session ID (valid UUID)",
+    "type": "string"
+  },
+  "currency": {
+    "description": "ISO 4217 currency code (e.g. USD)",
+    "maxLength": 3,
+    "minLength": 3,
+    "type": "string"
+  },
+  "line_items": {
+    "description": "Replacement line items",
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "price": {
+          "additionalProperties": false,
+          "properties": {
+            "amount": {
+              "description": "Price in smallest unit (cents)",
+              "minimum": 0,
+              "type": "number"
+            },
+            "currency": {
+              "description": "ISO 4217 currency code",
+              "maxLength": 3,
+              "minLength": 3,
+              "type": "string"
+            }
+          },
+          "required": [
+            "amount",
+            "currency"
+          ],
+          "type": "object"
+        },
+        "product_id": {
+          "description": "Product identifier",
+          "minLength": 1,
+          "type": "string"
+        },
+        "quantity": {
+          "description": "Quantity",
+          "exclusiveMinimum": 0,
+          "type": "integer"
+        },
+        "title": {
+          "description": "Product title",
+          "minLength": 1,
+          "type": "string"
+        }
+      },
+      "required": [
+        "product_id",
+        "title",
+        "quantity",
+        "price"
+      ],
+      "type": "object"
+    },
+    "minItems": 1,
+    "type": "array"
+  }
+}

addedInput schema / required

Added value: +[
+  "checkout_id",
+  "currency",
+  "line_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: -{
-  "checkout_id": {
-    "description": "UCP checkout session ID (valid UUID)",
-    "type": "string"
-  },
-  "currency": {
-    "description": "ISO 4217 currency code (e.g. USD)",
-    "maxLength": 3,
-    "minLength": 3,
-    "type": "string"
-  },
-  "line_items": {
-    "description": "Replacement line items",
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "price": {
-          "additionalProperties": false,
-          "properties": {
-            "amount": {
-              "description": "Price in smallest unit (cents)",
-              "minimum": 0,
-              "type": "number"
-            },
-            "currency": {
-              "description": "ISO 4217 currency code",
-              "maxLength": 3,
-              "minLength": 3,
-              "type": "string"
-            }
-          },
-          "required": [
-            "amount",
-            "currency"
-          ],
-          "type": "object"
-        },
-        "product_id": {
-          "description": "Product identifier",
-          "minLength": 1,
-          "type": "string"
-        },
-        "quantity": {
-          "description": "Quantity",
-          "exclusiveMinimum": 0,
-          "type": "integer"
-        },
-        "title": {
-          "description": "Product title",
-          "minLength": 1,
-          "type": "string"
-        }
-      },
-      "required": [
-        "product_id",
-        "title",
-        "quantity",
-        "price"
-      ],
-      "type": "object"
-    },
-    "minItems": 1,
-    "type": "array"
-  }
-}

removedInput schema / required

Removed value: -[
-  "checkout_id",
-  "currency",
-  "line_items"
-]

changedOutput schema / (root)

Previous value: -{
-  "$schema": "http://json-schema.org/draft-07/schema#",
-  "additionalProperties": false,
-  "properties": {
-    "created_at": {
-      "type": "string"
-    },
-    "currency": {
-      "type": "string"
-    },
-    "extensions": {
-      "additionalProperties": false,
-      "properties": {
-        "warnings": {
-          "items": {
-            "additionalProperties": false,
-            "properties": {
-              "code": {
-                "type": "string"
-              },
-              "disclosure_url": {
-                "type": "string"
-              },
-              "message": {
-                "type": "string"
-              },
-              "severity": {
-                "enum": [
-                  "info",
-                  "caution",
-                  "critical"
-                ],
-                "type": "string"
-              }
-            },
-            "required": [
-              "code",
-              "message",
-              "severity"
-            ],
-            "type": "object"
-          },
-          "type": "array"
-        }
-      },
-      "type": "object"
-    },
-    "id": {
-      "type": "string"
-    },
-    "idempotency_key": {
-      "type": "string"
-    },
-    "intent": {
-      "additionalProperties": false,
-      "properties": {
-        "action": {
-          "type": "string"
-        },
-        "context": {
-          "type": "string"
-        },
-        "locale": {
-          "type": "string"
-        }
-      },
-      "required": [
-        "action"
-      ],
-      "type": "object"
-    },
-    "label": {
-      "type": "string"
-    },
-    "line_items": {
-      "items": {
-        "additionalProperties": false,
-        "properties": {
-          "id": {
-            "type": "string"
-          },
-          "price": {
-            "additionalProperties": false,
-            "properties": {
-              "amount": {
-                "type": "number"
-              },
-              "currency": {
-                "type": "string"
-              }
-            },
-            "required": [
-              "amount",
-              "currency"
-            ],
-            "type": "object"
-          },
-          "product_id": {
-            "type": "string"
-          },
-          "quantity": {
-            "type": "number"
-          },
-          "title": {
-            "type": "string"
-          }
-        },
-        "required": [
-          "id",
-          "product_id",
-          "title",
-          "quantity",
-          "price"
-        ],
-        "type": "object"
-      },
-      "type": "array"
-    },
-    "status": {
-      "enum": [
-        "incomplete",
-        "requires_escalation",
-        "ready_for_complete",
-        "complete_in_progress",
-        "completed",
-        "canceled"
-      ],
-      "type": "string"
-    },
-    "totals": {
-      "items": {
-        "additionalProperties": false,
-        "properties": {
-          "amount": {
-            "type": "number"
-          },
-          "currency": {
-            "type": "string"
-          },
-          "label": {
-            "type": "string"
-          }
-        },
-        "required": [
-          "label",
-          "amount",
-          "currency"
-        ],
-        "type": "object"
-      },
-      "type": "array"
-    },
-    "updated_at": {
-      "type": "string"
-    }
-  },
-  "required": [
-    "id",
-    "status",
-    "currency",
-    "line_items",
-    "totals",
-    "created_at",
-    "updated_at"
-  ],
-  "type": "object"
-}New value: +null

First observedApr 28, 2026

TDQS

A4.7/5.0

Behavior5/5

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

The description goes well beyond the annotations by explaining that a payment mandate is required, how to send it via body or header, the exact fields it must carry, and that currency mismatch causes outright denial. It also clarifies the cap enforcement against the cart total, providing rich behavioral context.

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?

The description is efficiently structured: the core purpose is front-loaded, followed by a clearly flagged payment-mandate section. Every sentence carries operational value, and the formatting makes the critical warning easy to notice.

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?

For a tool of this complexity, the description covers the essential operational context: replacement semantics, status precondition, payment mandate requirements, and validation behavior. The existence of an output schema covers return-value expectations, so nothing critical is missing.

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

Parameters4/5

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

Schema coverage is 100%, so the schema already documents each parameter. The description adds meaningful semantic context beyond the schema, especially around payment_mandate: how to pass it, what it must contain, and the currency-matching rule. This elevates it above the baseline.

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 states a clear, specific action: 'Update a UCP checkout session by fully replacing all line items.' This distinguishes it from sibling tools like ucp_create_checkout and complete_checkout, and the resource and operation are unambiguous.

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?

The description provides a concrete usage condition ('Only allowed when status is incomplete') and details critical operational requirements like the payment mandate. It does not explicitly name alternative tools or say when not to use it, so it stops just short of a perfect score.

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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