Trusteed Agentic Commerce

ucp_get_checkout

Read-onlyIdempotent

Retrieve a UCP checkout session by ID. Returns the current state of the checkout. Use ONLY for a checkout session created with ucp_create_checkout (Universal Commerce Protocol); for the standard flow (create_cart, preview_checkout, complete_checkout) do not call this tool. Checkout guide: read the MCP resource trusteed://guides/checkout.

Input Schema

Name	Required	Description
`meta`	No	UCP request metadata. meta['ucp-agent'].profile = URL of the platform profile; it must be an https URL without credentials (at most 2048 characters).
`agent_key`	No	Sandbox credential from `create_sandbox_key`. Use this when your client cannot set an `Authorization: Bearer` header.
`checkout_id`	Yes	UCP checkout session ID (valid UUID)

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 17, 2026

changedOutput schema / (root)

Previous value: -{
-  "$schema": "http://json-schema.org/draft-07/schema#",
-  "additionalProperties": true,
-  "properties": {
-    "approval_url": {
-      "type": "string"
-    },
-    "created_at": {
-      "type": "string"
-    },
-    "currency": {
-      "type": "string"
-    },
-    "expires_at": {
-      "description": "ISO-8601 UTC instant at which this checkout SESSION stops being usable. It is not a stock reservation and not a price guarantee.",
-      "type": "string"
-    },
-    "expires_in_seconds": {
-      "description": "Whole seconds left on this checkout SESSION at response time (0 when already past). It is not a stock reservation and not a price guarantee.",
-      "minimum": 0,
-      "type": "integer"
-    },
-    "extensions": {
-      "additionalProperties": {},
-      "description": "`warnings[]` with `code`, `message`, `severity`.",
-      "type": "object"
-    },
-    "fulfillment": {
-      "additionalProperties": {},
-      "type": "object"
-    },
-    "id": {
-      "type": "string"
-    },
-    "idempotency_key": {
-      "type": "string"
-    },
-    "intent": {
-      "additionalProperties": {},
-      "type": "object"
-    },
-    "label": {
-      "type": "string"
-    },
-    "line_items": {
-      "items": {
-        "additionalProperties": true,
-        "properties": {
-          "id": {
-            "type": "string"
-          },
-          "price": {
-            "additionalProperties": true,
-            "properties": {
-              "amount": {
-                "type": "number"
-              },
-              "currency": {
-                "type": "string"
-              }
-            },
-            "required": [
-              "amount",
-              "currency"
-            ],
-            "type": "object"
-          },
-          "product_id": {
-            "type": "string"
-          },
-          "quantity": {
-            "type": "number"
-          },
-          "title": {
-            "type": "string"
-          },
-          "variant_id": {
-            "type": "string"
-          },
-          "variant_title": {
-            "type": "string"
-          }
-        },
-        "required": [
-          "id",
-          "product_id",
-          "title",
-          "quantity",
-          "price"
-        ],
-        "type": "object"
-      },
-      "type": "array"
-    },
-    "next_action": {
-      "additionalProperties": {},
-      "description": "Only when a person must approve or pay: `url`, `kind`, `retry`.",
-      "type": "object"
-    },
-    "next_step": {
-      "description": "Next-action code, not a tool name: provide_shipping_destination, refresh_shipping_rates, choose_shipping_option, preview_ucp_checkout, review_not_available_in_ucp.",
-      "type": "string"
-    },
-    "next_step_message": {
-      "type": "string"
-    },
-    "payment_options": {
-      "description": "When present, ask the person which option they want; never choose for them.",
-      "items": {
-        "additionalProperties": {},
-        "type": "object"
-      },
-      "type": "array"
-    },
-    "status": {
-      "enum": [
-        "incomplete",
-        "requires_escalation",
-        "ready_for_complete",
-        "complete_in_progress",
-        "completed",
-        "canceled"
-      ],
-      "type": "string"
-    },
-    "totals": {
-      "items": {
-        "additionalProperties": true,
-        "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

Changed1 schema field changedOct 16, 2026

changedOutput schema / properties / next_step / description

Previous value: -"Next-action code, not a tool name: provide_shipping_destination, refresh_shipping_rates, choose_shipping_option, review_not_available_in_ucp."New value: +"Next-action code, not a tool name: provide_shipping_destination, refresh_shipping_rates, choose_shipping_option, preview_ucp_checkout, review_not_available_in_ucp."

Changed1 schema field changedOct 16, 2026

changedOutput schema / properties / next_step / description

Previous value: -"Next-action code, not a tool name: provide_shipping_destination, refresh_shipping_rates, choose_shipping_option, ask_user_payment_method."New value: +"Next-action code, not a tool name: provide_shipping_destination, refresh_shipping_rates, choose_shipping_option, review_not_available_in_ucp."

Changed1 schema field changedOct 15, 2026

addedOutput schema / properties / next_step / description

Added value: +"Next-action code, not a tool name: provide_shipping_destination, refresh_shipping_rates, choose_shipping_option, ask_user_payment_method."

Changed17 schema fields changedOct 14, 2026

changedOutput schema / properties / extensions / additionalProperties
```
Previous value: -trueNew value: +{}
```

addedOutput schema / properties / extensions / description

Added value: +"`warnings[]` with `code`, `message`, `severity`."

removedOutput schema / properties / extensions / properties

Removed value: -{
-  "warnings": {
-    "items": {
-      "additionalProperties": true,
-      "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"
-  }
-}

changedOutput schema / properties / fulfillment / additionalProperties
```
Previous value: -trueNew value: +{}
```

removedOutput schema / properties / fulfillment / properties

Removed value: -{
-  "destination": {
-    "additionalProperties": true,
-    "properties": {
-      "city": {
-        "type": "string"
-      },
-      "country_code": {
-        "type": "string"
-      },
-      "province_code": {
-        "type": "string"
-      },
-      "zip": {
-        "type": "string"
-      }
-    },
-    "required": [
-      "city",
-      "country_code",
-      "zip"
-    ],
-    "type": "object"
-  },
-  "options": {
-    "items": {
-      "additionalProperties": true,
-      "properties": {
-        "authoritative": {
-          "type": "boolean"
-        },
-        "estimated_delivery": {
-          "type": "string"
-        },
-        "id": {
-          "type": "string"
-        },
-        "price": {
-          "additionalProperties": true,
-          "properties": {
-            "amount": {
-              "type": "number"
-            },
-            "currency": {
-              "type": "string"
-            }
-          },
-          "required": [
-            "amount",
-            "currency"
-          ],
-          "type": "object"
-        },
-        "source": {
-          "enum": [
-            "platform",
-            "merchant_policy",
-            "estimated"
-          ],
-          "type": "string"
-        },
-        "title": {
-          "type": "string"
-        }
-      },
-      "required": [
-        "id",
-        "title",
-        "price",
-        "source",
-        "authoritative"
-      ],
-      "type": "object"
-    },
-    "type": "array"
-  },
-  "selected_option_id": {
-    "type": "string"
-  }
-}

changedOutput schema / properties / intent / additionalProperties
```
Previous value: -trueNew value: +{}
```

removedOutput schema / properties / intent / properties

Removed value: -{
-  "action": {
-    "type": "string"
-  },
-  "context": {
-    "type": "string"
-  },
-  "locale": {
-    "type": "string"
-  }
-}

removedOutput schema / properties / intent / required
```
Removed value: -[
-  "action"
-]
```
changedOutput schema / properties / next_action / additionalProperties
```
Previous value: -trueNew value: +{}
```

addedOutput schema / properties / next_action / description

Added value: +"Only when a person must approve or pay: `url`, `kind`, `retry`."

removedOutput schema / properties / next_action / properties

Removed value: -{
-  "actor": {
-    "const": "buyer",
-    "type": "string"
-  },
-  "do": {
-    "enum": [
-      "approve",
-      "pay"
-    ],
-    "type": "string"
-  },
-  "instruction": {
-    "type": "string"
-  },
-  "reuse_arguments": {
-    "items": {
-      "enum": [
-        "checkout_session_id",
-        "checkout_id",
-        "idempotency_key"
-      ],
-      "type": "string"
-    },
-    "type": "array"
-  },
-  "then_call": {
-    "maxLength": 64,
-    "minLength": 1,
-    "type": "string"
-  },
-  "url": {
-    "type": "string"
-  }
-}

removedOutput schema / properties / next_action / required

Removed value: -[
-  "actor",
-  "do",
-  "url",
-  "instruction"
-]

removedOutput schema / properties / next_step / const
```
Removed value: -"ask_user_payment_method"
```

addedOutput schema / properties / payment_options / description

Added value: +"When present, ask the person which option they want; never choose for them."

changedOutput schema / properties / payment_options / items / additionalProperties
```
Previous value: -trueNew value: +{}
```

removedOutput schema / properties / payment_options / items / properties

Removed value: -{
-  "available": {
-    "type": "boolean"
-  },
-  "charges_without_approval": {
-    "const": true,
-    "type": "boolean"
-  },
-  "funding_source": {
-    "anyOf": [
-      {
-        "enum": [
-          "platform_test_card",
-          "platform_test_wallet",
-          "buyer_wallet"
-        ],
-        "type": "string"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  },
-  "id": {
-    "enum": [
-      "demo_card",
-      "demo_wallet",
-      "own_wallet",
-      "merchant_card",
-      "paypal",
-      "kyapay"
-    ],
-    "type": "string"
-  },
-  "label": {
-    "type": "string"
-  },
-  "rail": {
-    "enum": [
-      "stripe",
-      "x402",
-      "kyapay",
-      "paypal"
-    ],
-    "type": "string"
-  },
-  "reason_unavailable": {
-    "enum": [
-      "coming_soon",
-      "not_enabled",
-      "currency_not_supported",
-      "unsupported_on_this_tool"
-    ],
-    "type": "string"
-  }
-}

removedOutput schema / properties / payment_options / items / required

Removed value: -[
-  "id",
-  "label",
-  "rail",
-  "funding_source",
-  "available"
-]

Changed1 schema field changedOct 13, 2026
- addedOutput schema / properties / payment_options / items / properties / charges_without_approval
```
Added value: +{
+  "const": true,
+  "type": "boolean"
+}
```

Changed3 schema fields changedOct 13, 2026

changedOutput schema / properties / payment_options / items / properties / id / enum

Previous value: -[
-  "demo_card",
-  "demo_wallet",
-  "own_wallet",
-  "merchant_card",
-  "kyapay"
-]New value: +[
+  "demo_card",
+  "demo_wallet",
+  "own_wallet",
+  "merchant_card",
+  "paypal",
+  "kyapay"
+]

changedOutput schema / properties / payment_options / items / properties / rail / enum

Previous value: -[
-  "stripe",
-  "x402",
-  "kyapay"
-]New value: +[
+  "stripe",
+  "x402",
+  "kyapay",
+  "paypal"
+]

changedOutput schema / properties / payment_options / items / properties / reason_unavailable / enum

Previous value: -[
-  "coming_soon",
-  "not_enabled",
-  "currency_not_supported"
-]New value: +[
+  "coming_soon",
+  "not_enabled",
+  "currency_not_supported",
+  "unsupported_on_this_tool"
+]

Changed1 schema field changedOct 11, 2026

addedInput schema / properties / meta

Added value: +{
+  "description": "UCP request metadata. meta['ucp-agent'].profile = URL of the platform profile; it must be an https URL without credentials (at most 2048 characters)."
+}

Changed2 schema fields changedOct 10, 2026

addedOutput schema / properties / expires_at

Added value: +{
+  "description": "ISO-8601 UTC instant at which this checkout SESSION stops being usable. It is not a stock reservation and not a price guarantee.",
+  "type": "string"
+}

addedOutput schema / properties / expires_in_seconds

Added value: +{
+  "description": "Whole seconds left on this checkout SESSION at response time (0 when already past). It is not a stock reservation and not a price guarantee.",
+  "minimum": 0,
+  "type": "integer"
+}

Changed1 schema field changedOct 10, 2026

changedOutput schema / properties / payment_options / items / properties / reason_unavailable / enum

Previous value: -[
-  "coming_soon",
-  "not_enabled"
-]New value: +[
+  "coming_soon",
+  "not_enabled",
+  "currency_not_supported"
+]

Changed1 schema field changedOct 5, 2026

changedOutput schema / properties / payment_options / items / properties / id / enum

Previous value: -[
-  "demo_card",
-  "demo_wallet",
-  "own_wallet",
-  "kyapay"
-]New value: +[
+  "demo_card",
+  "demo_wallet",
+  "own_wallet",
+  "merchant_card",
+  "kyapay"
+]

Changed3 schema fields changedOct 1, 2026

addedOutput schema / properties / fulfillment

Added value: +{
+  "additionalProperties": true,
+  "properties": {
+    "destination": {
+      "additionalProperties": true,
+      "properties": {
+        "city": {
+          "type": "string"
+        },
+        "country_code": {
+          "type": "string"
+        },
+        "province_code": {
+          "type": "string"
+        },
+        "zip": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "city",
+        "country_code",
+        "zip"
+      ],
+      "type": "object"
+    },
+    "options": {
+      "items": {
+        "additionalProperties": true,
+        "properties": {
+          "authoritative": {
+            "type": "boolean"
+          },
+          "estimated_delivery": {
+            "type": "string"
+          },
+          "id": {
+            "type": "string"
+          },
+          "price": {
+            "additionalProperties": true,
+            "properties": {
+              "amount": {
+                "type": "number"
+              },
+              "currency": {
+                "type": "string"
+              }
+            },
+            "required": [
+              "amount",
+              "currency"
+            ],
+            "type": "object"
+          },
+          "source": {
+            "enum": [
+              "platform",
+              "merchant_policy",
+              "estimated"
+            ],
+            "type": "string"
+          },
+          "title": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "id",
+          "title",
+          "price",
+          "source",
+          "authoritative"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "selected_option_id": {
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

addedOutput schema / properties / line_items / items / properties / variant_id
```
Added value: +{
+  "type": "string"
+}
```
addedOutput schema / properties / line_items / items / properties / variant_title
```
Added value: +{
+  "type": "string"
+}
```

Changed3 schema fields changedSep 28, 2026

addedOutput schema / properties / next_step

Added value: +{
+  "const": "ask_user_payment_method",
+  "type": "string"
+}

addedOutput schema / properties / next_step_message
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / payment_options

Added value: +{
+  "items": {
+    "additionalProperties": true,
+    "properties": {
+      "available": {
+        "type": "boolean"
+      },
+      "funding_source": {
+        "anyOf": [
+          {
+            "enum": [
+              "platform_test_card",
+              "platform_test_wallet",
+              "buyer_wallet"
+            ],
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "id": {
+        "enum": [
+          "demo_card",
+          "demo_wallet",
+          "own_wallet",
+          "kyapay"
+        ],
+        "type": "string"
+      },
+      "label": {
+        "type": "string"
+      },
+      "rail": {
+        "enum": [
+          "stripe",
+          "x402",
+          "kyapay"
+        ],
+        "type": "string"
+      },
+      "reason_unavailable": {
+        "enum": [
+          "coming_soon",
+          "not_enabled"
+        ],
+        "type": "string"
+      }
+    },
+    "required": [
+      "id",
+      "label",
+      "rail",
+      "funding_source",
+      "available"
+    ],
+    "type": "object"
+  },
+  "type": "array"
+}

Changed2 schema fields changedSep 27, 2026

addedOutput schema / properties / approval_url
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / next_action

Added value: +{
+  "additionalProperties": true,
+  "properties": {
+    "actor": {
+      "const": "buyer",
+      "type": "string"
+    },
+    "do": {
+      "enum": [
+        "approve",
+        "pay"
+      ],
+      "type": "string"
+    },
+    "instruction": {
+      "type": "string"
+    },
+    "reuse_arguments": {
+      "items": {
+        "enum": [
+          "checkout_session_id",
+          "checkout_id",
+          "idempotency_key"
+        ],
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "then_call": {
+      "maxLength": 64,
+      "minLength": 1,
+      "type": "string"
+    },
+    "url": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "actor",
+    "do",
+    "url",
+    "instruction"
+  ],
+  "type": "object"
+}

Changed2 schema fields changedSep 22, 2026

addedInput schema / properties / agent_key

Added value: +{
+  "description": "Sandbox credential from `create_sandbox_key`. Use this when your client cannot set an `Authorization: Bearer` header.",
+  "type": "string"
+}

removedInput schema / properties / payment_mandate

Removed value: -{
-  "anyOf": [
-    {
-      "additionalProperties": {},
-      "type": "object"
-    },
-    {
-      "type": "string"
-    }
-  ],
-  "description": "Payment mandate with `mandate_id`, `max_amount_cents` (integer, minor units), `currency` (3 letters, must match the cart's), `exp` (expiry as an INTEGER of Unix seconds — not an ISO 8601 date string), `sub` (your agent id) and `aud` (the store slug this mandate is for, e.g. the slug in the URL you are calling — not a domain). Use this when your client cannot set an `X-Payment-Mandate` header."
-}

Changed1 schema field changedSep 21, 2026

changedInput schema / properties / payment_mandate / description

Previous value: -"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."New value: +"Payment mandate with `mandate_id`, `max_amount_cents` (integer, minor units), `currency` (3 letters, must match the cart's), `exp` (expiry as an INTEGER of Unix seconds — not an ISO 8601 date string), `sub` (your agent id) and `aud` (the store slug this mandate is for, e.g. the slug in the URL you are calling — not a domain). Use this when your client cannot set an `X-Payment-Mandate` header."

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

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered structurally. The description adds that it returns the checkout's current state and directs the agent to the checkout guide resource, which is useful routing context, though it says nothing about error behavior for invalid/expired IDs.

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?

Four short sentences, front-loaded with the action and return value, then the routing constraint, then the guide pointer. Every sentence earns its place with no redundancy.

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 annotations covering the safety profile and no output schema, the description adequately states what the call returns and when it applies. It could note failure modes (expired or unknown checkout IDs), but for a simple read tool it is essentially complete.

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 checkout_id, agent_key and meta are already documented in the schema, including the UUID format and credential fallback. The description adds no syntax or format detail beyond the schema, so the 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?

States a specific verb and resource ('Retrieve a UCP checkout session by ID') and immediately describes what it returns ('the current state of the checkout'). It also distinguishes itself from the standard flow by naming the sibling tools it must not be used with.

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

Usage Guidelines5/5

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

Gives an explicit precondition ('Use ONLY for a checkout session created with ucp_create_checkout'), an explicit exclusion ('for the standard flow (create_cart, preview_checkout, complete_checkout) do not call this tool'), and points to a guide resource for further context.

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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