diff --git a/schema/content-descriptor.json b/schema/content-descriptor.json
index 2e6ceba9b..cd122aa17 100644
--- a/schema/content-descriptor.json
+++ b/schema/content-descriptor.json
@@ -14,6 +14,14 @@
     },
     "digest": {
       "$ref": "defs-image.json#definitions/digest"
+    },
+    "urls": {
+      "description": "a list of urls from which this object may be downloaded",
+      "type": "array",
+      "items": {
+        "type": "string",
+        "format": "uri"
+      }
     }
   },
   "required": [
diff --git a/schema/defs-image.json b/schema/defs-image.json
index c1884636c..b0046a02c 100644
--- a/schema/defs-image.json
+++ b/schema/defs-image.json
@@ -32,6 +32,14 @@
         "digest": {
           "$ref": "#definitions/digest"
         },
+        "urls": {
+          "description": "a list of urls from which this object may be downloaded",
+          "type": "array",
+          "items": {
+            "type": "string",
+            "format": "uri"
+          }
+        },
         "platform": {
           "id": "https://opencontainers.org/schema/image/platform",
           "type": "object",
diff --git a/schema/fs.go b/schema/fs.go
index ab344db6f..1dea532fb 100644
--- a/schema/fs.go
+++ b/schema/fs.go
@@ -205,95 +205,98 @@ var _escData = map[string]*_escFile{
 	"/config-schema.json": {
 		local:   "config-schema.json",
 		size:    774,
-		modtime: 1477035771,
+		modtime: 1478057674,
 		compressed: `
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+AP//XlvgsQYDAAA=
 `,
 	},
 
 	"/content-descriptor.json": {
 		local:   "content-descriptor.json",
-		size:    637,
-		modtime: 1476325139,
+		size:    836,
+		modtime: 1478141504,
 		compressed: `
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+DLQ9RAMAAA==
 `,
 	},
 
 	"/defs-config.json": {
 		local:   "defs-config.json",
 		size:    2270,
-		modtime: 1476325139,
+		modtime: 1478057674,
 		compressed: `
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 `,
 	},
 
 	"/defs-image.json": {
 		local:   "defs-image.json",
-		size:    2550,
-		modtime: 1476325139,
+		size:    2753,
+		modtime: 1478141527,
 		compressed: `
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+csfz5bnvopSbNA06oleT/Wg32U3+BgAA//8jeF0swQoAAA==
 `,
 	},
 
 	"/defs.json": {
 		local:   "defs.json",
 		size:    3193,
-		modtime: 1476325139,
+		modtime: 1470056192,
 		compressed: `
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 `,
 	},
 
 	"/image-manifest-schema.json": {
 		local:   "image-manifest-schema.json",
 		size:    1032,
-		modtime: 1476325139,
+		modtime: 1470056192,
 		compressed: `
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 X3p8DwgEAAA=
 `,
 	},
@@ -301,14 +304,15 @@ X3p8DwgEAAA=
 	"/manifest-list-schema.json": {
 		local:   "manifest-list-schema.json",
 		size:    1010,
-		modtime: 1476325139,
+		modtime: 1470056192,
 		compressed: `
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+AA==
 `,
 	},
 
diff --git a/specs-go/v1/descriptor.go b/specs-go/v1/descriptor.go
index a086f1501..83dde9666 100644
--- a/specs-go/v1/descriptor.go
+++ b/specs-go/v1/descriptor.go
@@ -24,4 +24,7 @@ type Descriptor struct {
 
 	// Size specifies the size in bytes of the blob.
 	Size int64 `json:"size"`
+
+	// URLs specifies a list of URLs from which this object MAY be downloaded
+	URLs []string `json:"urls,omitempty"`
 }