mcp-gateway

ucp_get_checkout

Read-onlyIdempotent

Retrieve a UCP checkout session by ID. Returns the current state of the checkout. 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	Default
`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."
+}

Changed8 schema fields changedSep 17, 2026
- changedInput schema / 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"
+  }
+}

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

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"
-  }
-}

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

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

A4.8/5.0

Behavior5/5

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

Beyond the readOnly/idempotent hints, the description discloses that a payment mandate is mandatory even for this read, specifies the required fields, and gives exact denial conditions (currency mismatch, cap enforcement). This is material behavioral context an agent could not infer from annotations or schema alone.

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?

Every sentence earns its place: purpose, state returned, mandate requirement, transport alternatives, field requirements, and validation consequences. The structure front-loads the primary action and then gives the critical auth constraint.

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 single-checkout read with an output schema present, the description covers the essential call requirements, including the non-obvious mandate and validation rules. Nothing needed to correctly invoke the tool is missing.

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

Parameters5/5

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

Although schema coverage is 100%, the description adds significant meaning to payment_mandate: the exact fields it must carry, the header-vs-argument alternatives, and the currency/cap enforcement rules. It thus goes well beyond the schema's generic 'Payment mandate with fields' text.

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 ('Retrieve a UCP checkout session by ID') and clarifies it returns the current state. This clearly differentiates it from sibling mutation tools like ucp_create_checkout, ucp_update_checkout, and ucp_cancel_checkout.

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 intended use is clear from the retrieval semantics for a single checkout by ID, but the description does not explicitly name alternative tools or exclusion conditions. It does give concrete invocation guidance for the required payment mandate, which helps an agent use it correctly.

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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