diff --git a/README.md b/README.md
index af480d1..d219e66 100644
--- a/README.md
+++ b/README.md
@@ -157,6 +157,10 @@ However, nothing can stop you from just copying `cp0.json` (and `schema.json` if
 | value_flow | Information related to usage of stack and registers by instruction. Required.
 | value_flow.doc_stack | Free-form description of stack inputs and outputs. Usually the form is `[inputs] - [outputs]` where `[inputs]` are consumed stack values and `outputs` are produced stack values (top of stack is the last value). Required.
 | value_flow.inputs | Incoming values constraints. Required.
+| value_flow.inputs.registers | Defines how registers is used by instruction. Instruction must not operate on registers other than defined here. Required.
+| value_flow.inputs.registers[i] | Register which is access by instruction.
+| value_flow.inputs.registers[i].type | Type of register: "constant", "variable", "special". Required.
+| value_flow.inputs.registers[i].* | Properties for registers of each type are described below.
 | value_flow.inputs.stack | Defines how current stack is used by instruction. Instruction must not operate on stack entries other than defined here. Optional, input stack is unconstrained if absent.
 | value_flow.inputs.stack[i] | Stack entry or group of stack entries.
 | value_flow.inputs.stack[i].type | Type of stack entry. Can be one of "simple", "const", "conditional", "array". Required. 
@@ -350,6 +354,40 @@ Specifies a bunch of stack entries with length from variable `length_var`, usual
 1. Each variable name is unique across `operands`, `value_flow`, and `control_flow` sections of each instruction. Assumed that variables are immutable, so if variable `x` is defined both in inputs and outputs, it goes to output without any modification.
 2. Value flow describes only `cc` stack usage before the actual jump or call. Subsequent continuations may have a separate stack, so this will be defined in control flow section of this spec.
 
+### Register Specification and Examples
+#### constant
+```json
+{
+    "type": "constant",
+    "index": 0
+}
+```
+Represents `c{index}` register.
+
+#### variable
+```json
+{
+    "type": "variable",
+    "var_name": "i"
+}
+```
+Represents `c{{var_name}}` register. Its number is taken from variable `var_name`, defined in stack inputs or operands.
+
+#### special
+```json
+{
+    "type": "special",
+    "name": "gas"
+}
+```
+```json
+{
+    "type": "special",
+    "name": "cstate"
+}
+```
+Represents gas registers (used by app_gas instructions) and cstate (used by COMMIT instruction).
+
 ### Continuations Specification and Examples
 Each object represents a continuation, which can be constructed in several ways: 
 * from a variable (operand or stack)
diff --git a/cp0.json b/cp0.json
index ed26c5a..5560742 100644
--- a/cp0.json
+++ b/cp0.json
@@ -21357,7 +21357,10 @@
             { "type": "constant", "index": 0 }
           ]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 0 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21387,8 +21390,17 @@
       },
       "value_flow": {
         "doc_stack": "",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [
+            { "type": "variable", "var_name": "i" },
+            { "type": "constant", "index": 1 }
+          ]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 1 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21418,8 +21430,21 @@
       },
       "value_flow": {
         "doc_stack": "",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [
+            { "type": "variable", "var_name": "i" },
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
+          ]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
+          ]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21444,7 +21469,8 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "i", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "variable", "var_name": "i" }]
         },
         "outputs": { "stack": [{ "type": "simple", "name": "x" }] }
       },
@@ -21474,7 +21500,10 @@
             { "type": "simple", "name": "i", "value_types": ["Integer"] }
           ]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "variable", "var_name": "i" }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21633,9 +21662,13 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Continuation"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 0 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 0 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21665,9 +21698,13 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Continuation"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 1 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 1 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21692,9 +21729,16 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Continuation"] }
+          ],
+          "registers": [
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
           ]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 1 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21719,7 +21763,8 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Continuation"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 0 }]
         },
         "outputs": {
           "stack": [
@@ -21750,7 +21795,8 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Continuation"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 1 }]
         },
         "outputs": {
           "stack": [
@@ -21778,8 +21824,20 @@
       },
       "value_flow": {
         "doc_stack": "-",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
+          ]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
+          ]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21870,8 +21928,14 @@
       },
       "value_flow": {
         "doc_stack": "-",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 0 }]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 1 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -21893,8 +21957,20 @@
       },
       "value_flow": {
         "doc_stack": "-",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
+          ]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [
+            { "type": "constant", "index": 0 },
+            { "type": "constant", "index": 1 }
+          ]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -22060,7 +22136,10 @@
       },
       "value_flow": {
         "doc_stack": " - n c",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 3 }]
+        },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "n", "value_types": ["Integer"] },
@@ -29762,8 +29841,14 @@
       },
       "value_flow": {
         "doc_stack": "-",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "special", "name": "gas" }]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "special", "name": "gas" }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -29788,9 +29873,13 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "g", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "special", "name": "gas" }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "special", "name": "gas" }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -29816,7 +29905,8 @@
         "outputs": {
           "stack": [
             { "type": "simple", "name": "g_c", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "special", "name": "gas" }]
         }
       },
       "control_flow": { "branches": [], "nobranch": true }
@@ -29839,8 +29929,17 @@
       },
       "value_flow": {
         "doc_stack": "-",
-        "inputs": { "stack": [] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [],
+          "registers": [
+            { "type": "constant", "index": 4 },
+            { "type": "constant", "index": 5 }
+          ]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "special", "name": "cstate" }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -29862,11 +29961,15 @@
       },
       "value_flow": {
         "doc_stack": "- x",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         }
       },
       "control_flow": { "branches": [], "nobranch": true }
@@ -29892,12 +29995,14 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "y", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "z", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         }
       },
       "control_flow": { "branches": [], "nobranch": true }
@@ -29923,9 +30028,13 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -29950,9 +30059,13 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -29982,7 +30095,10 @@
       },
       "value_flow": {
         "doc_stack": " - x",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
@@ -30009,7 +30125,10 @@
       },
       "value_flow": {
         "doc_stack": " - D 32",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "x", "value_types": ["Slice", "Null"] },
@@ -30040,7 +30159,8 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "i", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
         "outputs": {
           "stack": [
@@ -30084,7 +30204,8 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "i", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
         "outputs": {
           "stack": [
@@ -30112,7 +30233,10 @@
       },
       "value_flow": {
         "doc_stack": "- t",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": {
           "stack": [{ "type": "simple", "name": "t", "value_types": ["Tuple"] }]
         }
@@ -30137,7 +30261,10 @@
       },
       "value_flow": {
         "doc_stack": "- t",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": {
           "stack": [{ "type": "simple", "name": "t", "value_types": ["Tuple"] }]
         }
@@ -30162,7 +30289,10 @@
       },
       "value_flow": {
         "doc_stack": "- i",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "i", "value_types": ["Integer"] }
@@ -30192,7 +30322,8 @@
         "inputs": {
           "stack": [
             { "type": "simple", "name": "k", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
         "outputs": { "stack": [{ "type": "simple", "name": "x" }] }
       },
@@ -30225,7 +30356,10 @@
       },
       "value_flow": {
         "doc_stack": " - x",
-        "inputs": { "stack": [] },
+        "inputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
         "outputs": { "stack": [{ "type": "simple", "name": "x" }] }
       },
       "control_flow": { "branches": [], "nobranch": true }
@@ -30252,9 +30386,13 @@
           "stack": [
             { "type": "simple", "name": "x" },
             { "type": "simple", "name": "k", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 7 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -30285,8 +30423,14 @@
       },
       "value_flow": {
         "doc_stack": "x - ",
-        "inputs": { "stack": [{ "type": "simple", "name": "x" }] },
-        "outputs": { "stack": [] }
+        "inputs": {
+          "stack": [{ "type": "simple", "name": "x" }],
+          "registers": [{ "type": "constant", "index": 7 }]
+        },
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 7 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33425,9 +33569,13 @@
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Cell"] },
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 5 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33453,9 +33601,13 @@
           "stack": [
             { "type": "simple", "name": "x", "value_types": ["Integer"] },
             { "type": "simple", "name": "y", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 5 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33482,9 +33634,13 @@
             { "type": "simple", "name": "x", "value_types": ["Integer"] },
             { "type": "simple", "name": "D", "value_types": ["Cell", "Null"] },
             { "type": "simple", "name": "y", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 5 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33507,9 +33663,13 @@
       "value_flow": {
         "doc_stack": "c - ",
         "inputs": {
-          "stack": [{ "type": "simple", "name": "c", "value_types": ["Cell"] }]
+          "stack": [{ "type": "simple", "name": "c", "value_types": ["Cell"] }],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 5 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33535,9 +33695,13 @@
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Cell"] },
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 5 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33563,9 +33727,13 @@
           "stack": [
             { "type": "simple", "name": "h", "value_types": ["Integer"] },
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
-        "outputs": { "stack": [] }
+        "outputs": {
+          "stack": [],
+          "registers": [{ "type": "constant", "index": 5 }]
+        }
       },
       "control_flow": { "branches": [], "nobranch": true }
     },
@@ -33591,12 +33759,14 @@
           "stack": [
             { "type": "simple", "name": "c", "value_types": ["Cell"] },
             { "type": "simple", "name": "x", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         },
         "outputs": {
           "stack": [
             { "type": "simple", "name": "fee", "value_types": ["Integer"] }
-          ]
+          ],
+          "registers": [{ "type": "constant", "index": 5 }]
         }
       },
       "control_flow": { "branches": [], "nobranch": true }
diff --git a/schema.json b/schema.json
index 7003d79..452e748 100644
--- a/schema.json
+++ b/schema.json
@@ -61,12 +61,54 @@
     "values": {
       "type": "object",
       "additionalProperties": false,
+      "required": ["registers"],
       "properties": {
         "stack": {
           "$ref": "#/definitions/stack"
+        },
+        "registers": {
+          "type": "array",
+          "title": "Register values",
+          "items": {
+            "$ref": "#/definitions/register_flow"
+          },
+          "additionalItems": false
         }
       }
     },
+    "register_flow": {
+      "title": "Register",
+      "description": "Represents read/write access to a register",
+      "oneOf": [
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "required": ["type", "index"],
+          "properties": {
+            "type": { "const": "constant" },
+            "index": { "type": "number" }
+          }
+        },
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "required": ["type", "var_name"],
+          "properties": {
+            "type": { "const": "variable" },
+            "var_name": { "$ref": "#/definitions/var_name" }
+          }
+        },
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "required": ["type", "name"],
+          "properties": {
+            "type": { "const": "special" },
+            "name": { "enum": ["gas", "cstate"] }
+          }
+        }
+      ]
+    },
     "stack": {
       "type": "array",
       "title": "Stack values",