diff --git a/cmd/urfave-cli-genflags/go.sum b/cmd/urfave-cli-genflags/go.sum
index 9821127..e59916d 100644
--- a/cmd/urfave-cli-genflags/go.sum
+++ b/cmd/urfave-cli-genflags/go.sum
@@ -1,5 +1,3 @@
-github.com/BurntSushi/toml v1.1.0 h1:ksErzDEI1khOiGPgpwuI7x2ebx/uXQNw7xJpn9Eq1+I=
-github.com/BurntSushi/toml v1.1.0/go.mod h1:CxXYINrC8qIiEnFrOxCa7Jy5BFHlXnUU2pbicEuybxQ=
 github.com/cpuguy83/go-md2man/v2 v2.0.2 h1:p1EgwI/C7NhT0JmVkwCD2ZBK8j4aeHQX2pMHHBfMQ6w=
 github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
@@ -10,7 +8,6 @@ github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673 h1:bAn7/zixMGCfxrRT
 github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673/go.mod h1:N3UwUGtsrSj3ccvlPHLoLsHnpR27oXr4ZE984MbSER8=
 golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
 golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
-golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
diff --git a/flag-spec.yaml b/flag-spec.yaml
index 66745c6..ea75670 100644
--- a/flag-spec.yaml
+++ b/flag-spec.yaml
@@ -9,47 +9,77 @@ flag_types:
       - name: Count
         type: int
         pointer: true
+      - name: Action
+        type: "func(*Context, bool) error"
   float64:
+    struct_fields:
+      - name: Action
+        type: "func(*Context, float64) error"
   Float64Slice:
     value_pointer: true
     skip_interfaces:
       - fmt.Stringer
+    struct_fields:
+      - name: Action
+        type: "func(*Context, []float64) error"
   int:
     struct_fields:
       - name: Base
         type: int
+      - name: Action
+        type: "func(*Context, int) error"
   IntSlice:
     value_pointer: true
     skip_interfaces:
       - fmt.Stringer
+    struct_fields:
+      - name: Action
+        type: "func(*Context, []int) error"
   int64:
     struct_fields:
       - name: Base
         type: int
+      - name: Action
+        type: "func(*Context, int64) error"
   Int64Slice:
     value_pointer: true
     skip_interfaces:
       - fmt.Stringer
+    struct_fields:
+      - name: Action
+        type: "func(*Context, []int64) error"
   uint:
     struct_fields:
       - name: Base
         type: int
+      - name: Action
+        type: "func(*Context, uint) error"
   UintSlice:
     value_pointer: true
     skip_interfaces:
       - fmt.Stringer
+    struct_fields:
+      - name: Action
+        type: "func(*Context, []uint) error"
   uint64:
     struct_fields:
       - name: Base
         type: int
+      - name: Action
+        type: "func(*Context, uint64) error"
   Uint64Slice:
     value_pointer: true
     skip_interfaces:
       - fmt.Stringer
+    struct_fields:
+      - name: Action
+        type: "func(*Context, []uint64) error"
   string:
     struct_fields:
       - name: TakesFile
         type: bool
+      - name: Action
+        type: "func(*Context, string) error"
   StringSlice:
     value_pointer: true
     skip_interfaces:
@@ -57,7 +87,12 @@ flag_types:
     struct_fields:
       - name: TakesFile
         type: bool
+      - name: Action
+        type: "func(*Context, []string) error"
   time.Duration:
+    struct_fields:
+      - name: Action
+        type: "func(*Context, time.Duration) error"
   Timestamp:
     value_pointer: true
     struct_fields:
@@ -65,12 +100,18 @@ flag_types:
         type: string
       - name: Timezone
         type: "*time.Location"
+      - name: Action
+        type: "func(*Context, *time.Time) error"
   Generic:
     no_destination_pointer: true
     struct_fields:
       - name: TakesFile
         type: bool
+      - name: Action
+        type: "func(*Context, interface{}) error"
   Path:
     struct_fields:
       - name: TakesFile
         type: bool
+      - name: Action
+        type: "func(*Context, Path) error"
diff --git a/zz_generated.flags.go b/zz_generated.flags.go
index 2c5bea0..68934c7 100644
--- a/zz_generated.flags.go
+++ b/zz_generated.flags.go
@@ -22,6 +22,8 @@ type Float64SliceFlag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, []float64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -92,6 +94,8 @@ type GenericFlag struct {
 	EnvVars []string
 
 	TakesFile bool
+
+	Action func(*Context, interface{}) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -165,6 +169,8 @@ type Int64SliceFlag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, []int64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -233,6 +239,8 @@ type IntSliceFlag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, []int) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -303,6 +311,8 @@ type PathFlag struct {
 	EnvVars []string
 
 	TakesFile bool
+
+	Action func(*Context, Path) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -370,6 +380,8 @@ type StringSliceFlag struct {
 	EnvVars []string
 
 	TakesFile bool
+
+	Action func(*Context, []string) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -442,6 +454,8 @@ type TimestampFlag struct {
 	Layout string
 
 	Timezone *time.Location
+
+	Action func(*Context, *time.Time) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -515,6 +529,8 @@ type Uint64SliceFlag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, []uint64) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -555,6 +571,8 @@ type UintSliceFlag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, []uint) error
 }
 
 // IsSet returns whether or not the flag has been set through env or file
@@ -597,6 +615,8 @@ type BoolFlag struct {
 	EnvVars []string
 
 	Count *int
+
+	Action func(*Context, bool) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -662,6 +682,8 @@ type Float64Flag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, float64) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -737,6 +759,8 @@ type IntFlag struct {
 	EnvVars []string
 
 	Base int
+
+	Action func(*Context, int) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -812,6 +836,8 @@ type Int64Flag struct {
 	EnvVars []string
 
 	Base int
+
+	Action func(*Context, int64) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -887,6 +913,8 @@ type StringFlag struct {
 	EnvVars []string
 
 	TakesFile bool
+
+	Action func(*Context, string) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -952,6 +980,8 @@ type DurationFlag struct {
 
 	Aliases []string
 	EnvVars []string
+
+	Action func(*Context, time.Duration) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -1027,6 +1057,8 @@ type UintFlag struct {
 	EnvVars []string
 
 	Base int
+
+	Action func(*Context, uint) error
 }
 
 // String returns a readable representation of this value (for usage defaults)
@@ -1102,6 +1134,8 @@ type Uint64Flag struct {
 	EnvVars []string
 
 	Base int
+
+	Action func(*Context, uint64) error
 }
 
 // String returns a readable representation of this value (for usage defaults)