diff --git a/README.md b/README.md
index 9c03075..d0dd2d2 100644
--- a/README.md
+++ b/README.md
@@ -89,16 +89,16 @@ import (
 
     "github.com/xdrm-io/aicra"
     "github.com/xdrm-io/aicra/api"
-    "github.com/xdrm-io/aicra/datatype/builtin"
+    "github.com/xdrm-io/aicra/validator/builtin"
 )
 
 func main() {
     builder := &aicra.Builder{}
 
-    // register data validators
-    builder.AddType(builtin.BoolDataType{})
-    builder.AddType(builtin.UintDataType{})
-    builder.AddType(builtin.StringDataType{})
+    // add custom type validators
+    builder.Validate(validator.BoolDataType{})
+    builder.Validate(validator.UintDataType{})
+    builder.Validate(validator.StringDataType{})
 
     // load your configuration
     config, err := os.Open("api.json")
diff --git a/builder.go b/builder.go
index 0fc8d3b..fc17243 100644
--- a/builder.go
+++ b/builder.go
@@ -5,9 +5,9 @@ import (
 	"io"
 	"net/http"
 
-	"github.com/xdrm-io/aicra/datatype"
 	"github.com/xdrm-io/aicra/internal/config"
 	"github.com/xdrm-io/aicra/internal/dynfunc"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 // Builder for an aicra server
@@ -31,18 +31,18 @@ type apiHandler struct {
 	dyn    *dynfunc.Handler
 }
 
-// AddType adds an available datatype to the api definition
-func (b *Builder) AddType(t datatype.T) error {
+// Validate adds an available Type to validate in the api definition
+func (b *Builder) Validate(t validator.Type) error {
 	if b.conf == nil {
 		b.conf = &config.Server{}
 	}
 	if b.conf.Services != nil {
 		return errLateType
 	}
-	if b.conf.Types == nil {
-		b.conf.Types = make([]datatype.T, 0)
+	if b.conf.Validators == nil {
+		b.conf.Validators = make([]validator.Type, 0)
 	}
-	b.conf.Types = append(b.conf.Types, t)
+	b.conf.Validators = append(b.conf.Validators, t)
 	return nil
 }
 
diff --git a/builder_test.go b/builder_test.go
index 8bae2ac..fbbebe0 100644
--- a/builder_test.go
+++ b/builder_test.go
@@ -8,26 +8,26 @@ import (
 	"testing"
 
 	"github.com/xdrm-io/aicra/api"
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func addBuiltinTypes(b *Builder) error {
-	if err := b.AddType(builtin.AnyDataType{}); err != nil {
+	if err := b.Validate(validator.AnyType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.BoolDataType{}); err != nil {
+	if err := b.Validate(validator.BoolType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.FloatDataType{}); err != nil {
+	if err := b.Validate(validator.FloatType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.IntDataType{}); err != nil {
+	if err := b.Validate(validator.IntType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.StringDataType{}); err != nil {
+	if err := b.Validate(validator.StringType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.UintDataType{}); err != nil {
+	if err := b.Validate(validator.UintType{}); err != nil {
 		return err
 	}
 	return nil
@@ -35,7 +35,7 @@ func addBuiltinTypes(b *Builder) error {
 
 func TestAddType(t *testing.T) {
 	builder := &Builder{}
-	err := builder.AddType(builtin.BoolDataType{})
+	err := builder.Validate(validator.BoolType{})
 	if err != nil {
 		t.Fatalf("unexpected error: %s", err)
 	}
@@ -43,7 +43,7 @@ func TestAddType(t *testing.T) {
 	if err != nil {
 		t.Fatalf("unexpected error: %s", err)
 	}
-	err = builder.AddType(builtin.FloatDataType{})
+	err = builder.Validate(validator.FloatType{})
 	if err != errLateType {
 		t.Fatalf("expected <%v> got <%v>", errLateType, err)
 	}
diff --git a/datatype/builtin/any.go b/datatype/builtin/any.go
deleted file mode 100644
index fdfd5f9..0000000
--- a/datatype/builtin/any.go
+++ /dev/null
@@ -1,26 +0,0 @@
-package builtin
-
-import (
-	"reflect"
-
-	"github.com/xdrm-io/aicra/datatype"
-)
-
-// AnyDataType is what its name tells
-type AnyDataType struct{}
-
-// Type returns the type of data
-func (AnyDataType) Type() reflect.Type {
-	return reflect.TypeOf(interface{}(nil))
-}
-
-// Build returns the validator
-func (AnyDataType) Build(typeName string, registry ...datatype.T) datatype.Validator {
-	// nothing if type not handled
-	if typeName != "any" {
-		return nil
-	}
-	return func(value interface{}) (interface{}, bool) {
-		return value, true
-	}
-}
diff --git a/datatype/datatype.go b/datatype/datatype.go
deleted file mode 100644
index 2e0a264..0000000
--- a/datatype/datatype.go
+++ /dev/null
@@ -1,23 +0,0 @@
-package datatype
-
-import (
-	"reflect"
-)
-
-// Validator returns whether a given value fulfills the datatype
-// and casts the value into a common go type.
-//
-// for example, if a validator checks for upper case strings,
-// whether the value is a []byte, a string or a []rune, if the
-// value matches the validator's checks, it will be cast it into
-// a common go type, say, string.
-type Validator func(value interface{}) (cast interface{}, valid bool)
-
-// T represents a datatype. The Build function returns a Validator if
-// it manages types with the name `typeDefinition` (from the configuration field "type"); else it or returns NIL if the type
-// definition does not match this datatype; the registry is passed to allow recursive datatypes (e.g. slices, structs, etc)
-// The datatype's validator (when input is valid) must return a cast's go type matching the `Type() reflect.Type`
-type T interface {
-	Type() reflect.Type
-	Build(typeDefinition string, registry ...T) Validator
-}
diff --git a/handler_test.go b/handler_test.go
index 00311f1..fe3327e 100644
--- a/handler_test.go
+++ b/handler_test.go
@@ -12,26 +12,26 @@ import (
 
 	"github.com/xdrm-io/aicra"
 	"github.com/xdrm-io/aicra/api"
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func addBuiltinTypes(b *aicra.Builder) error {
-	if err := b.AddType(builtin.AnyDataType{}); err != nil {
+	if err := b.Validate(validator.AnyType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.BoolDataType{}); err != nil {
+	if err := b.Validate(validator.BoolType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.FloatDataType{}); err != nil {
+	if err := b.Validate(validator.FloatType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.IntDataType{}); err != nil {
+	if err := b.Validate(validator.IntType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.StringDataType{}); err != nil {
+	if err := b.Validate(validator.StringType{}); err != nil {
 		return err
 	}
-	if err := b.AddType(builtin.UintDataType{}); err != nil {
+	if err := b.Validate(validator.UintType{}); err != nil {
 		return err
 	}
 	return nil
diff --git a/internal/config/config.go b/internal/config/config.go
index 1ac6fcc..cc529d0 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -7,13 +7,13 @@ import (
 	"net/http"
 	"strings"
 
-	"github.com/xdrm-io/aicra/datatype"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 // Server definition
 type Server struct {
-	Types    []datatype.T
-	Services []*Service
+	Validators []validator.Type
+	Services   []*Service
 }
 
 // Parse a configuration into a server. Server.Types must be set beforehand to
@@ -32,9 +32,9 @@ func (srv *Server) Parse(r io.Reader) error {
 }
 
 // validate implements the validator interface
-func (server Server) validate(datatypes ...datatype.T) error {
+func (server Server) validate(datatypes ...validator.Type) error {
 	for _, service := range server.Services {
-		err := service.validate(server.Types...)
+		err := service.validate(server.Validators...)
 		if err != nil {
 			return fmt.Errorf("%s '%s': %w", service.Method, service.Pattern, err)
 		}
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 030e027..5db787c 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -8,7 +8,7 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestLegalServiceName(t *testing.T) {
@@ -239,7 +239,7 @@ func TestParamEmptyRenameNoRename(t *testing.T) {
 		}
 	]`)
 	srv := &Server{}
-	srv.Types = append(srv.Types, builtin.AnyDataType{})
+	srv.Validators = append(srv.Validators, validator.AnyType{})
 	err := srv.Parse(r)
 	if err != nil {
 		t.Errorf("unexpected error: '%s'", err)
@@ -275,8 +275,8 @@ func TestOptionalParam(t *testing.T) {
 		}
 	]`)
 	srv := &Server{}
-	srv.Types = append(srv.Types, builtin.AnyDataType{})
-	srv.Types = append(srv.Types, builtin.BoolDataType{})
+	srv.Validators = append(srv.Validators, validator.AnyType{})
+	srv.Validators = append(srv.Validators, validator.BoolType{})
 	err := srv.Parse(r)
 	if err != nil {
 		t.Errorf("unexpected error: '%s'", err)
@@ -588,7 +588,7 @@ func TestParseParameters(t *testing.T) {
 
 		t.Run(fmt.Sprintf("method.%d", i), func(t *testing.T) {
 			srv := &Server{}
-			srv.Types = append(srv.Types, builtin.AnyDataType{})
+			srv.Validators = append(srv.Validators, validator.AnyType{})
 			err := srv.Parse(strings.NewReader(test.Raw))
 
 			if err == nil && test.Error != nil {
@@ -827,8 +827,8 @@ func TestServiceCollision(t *testing.T) {
 
 		t.Run(fmt.Sprintf("method.%d", i), func(t *testing.T) {
 			srv := &Server{}
-			srv.Types = append(srv.Types, builtin.StringDataType{})
-			srv.Types = append(srv.Types, builtin.UintDataType{})
+			srv.Validators = append(srv.Validators, validator.StringType{})
+			srv.Validators = append(srv.Validators, validator.UintType{})
 			err := srv.Parse(strings.NewReader(test.Config))
 
 			if err == nil && test.Error != nil {
@@ -997,9 +997,9 @@ func TestMatchSimple(t *testing.T) {
 
 		t.Run(fmt.Sprintf("method.%d", i), func(t *testing.T) {
 			srv := &Server{}
-			srv.Types = append(srv.Types, builtin.AnyDataType{})
-			srv.Types = append(srv.Types, builtin.IntDataType{})
-			srv.Types = append(srv.Types, builtin.BoolDataType{})
+			srv.Validators = append(srv.Validators, validator.AnyType{})
+			srv.Validators = append(srv.Validators, validator.IntType{})
+			srv.Validators = append(srv.Validators, validator.BoolType{})
 			err := srv.Parse(strings.NewReader(test.Config))
 
 			if err != nil {
@@ -1081,9 +1081,9 @@ func TestFindPriority(t *testing.T) {
 
 		t.Run(fmt.Sprintf("method.%d", i), func(t *testing.T) {
 			srv := &Server{}
-			srv.Types = append(srv.Types, builtin.AnyDataType{})
-			srv.Types = append(srv.Types, builtin.IntDataType{})
-			srv.Types = append(srv.Types, builtin.BoolDataType{})
+			srv.Validators = append(srv.Validators, validator.AnyType{})
+			srv.Validators = append(srv.Validators, validator.IntType{})
+			srv.Validators = append(srv.Validators, validator.BoolType{})
 			err := srv.Parse(strings.NewReader(test.Config))
 
 			if err != nil {
diff --git a/internal/config/parameter.go b/internal/config/parameter.go
index d0e5ab7..a22227b 100644
--- a/internal/config/parameter.go
+++ b/internal/config/parameter.go
@@ -3,7 +3,7 @@ package config
 import (
 	"reflect"
 
-	"github.com/xdrm-io/aicra/datatype"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 // Parameter represents a parameter definition (from api.json)
@@ -12,13 +12,13 @@ type Parameter struct {
 	Type        string `json:"type"`
 	Rename      string `json:"name,omitempty"`
 	Optional    bool
-	// ExtractType is the type the Validator will cast into
-	ExtractType reflect.Type
+	// GoType is the type the Validator will cast into
+	GoType reflect.Type
 	// Validator is inferred from the "type" property
-	Validator datatype.Validator
+	Validator validator.ValidateFunc
 }
 
-func (param *Parameter) validate(datatypes ...datatype.T) error {
+func (param *Parameter) validate(datatypes ...validator.Type) error {
 	if len(param.Description) < 1 {
 		return errMissingParamDesc
 	}
@@ -35,8 +35,8 @@ func (param *Parameter) validate(datatypes ...datatype.T) error {
 
 	// find validator
 	for _, dtype := range datatypes {
-		param.Validator = dtype.Build(param.Type, datatypes...)
-		param.ExtractType = dtype.Type()
+		param.Validator = dtype.Validator(param.Type, datatypes...)
+		param.GoType = dtype.GoType()
 		if param.Validator != nil {
 			break
 		}
diff --git a/internal/config/service.go b/internal/config/service.go
index 3b051ba..6d10d27 100644
--- a/internal/config/service.go
+++ b/internal/config/service.go
@@ -6,7 +6,7 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/xdrm-io/aicra/datatype"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 var braceRegex = regexp.MustCompile(`^{([a-z_-]+)}$`)
@@ -97,7 +97,7 @@ func (svc *Service) matchPattern(uri string) bool {
 }
 
 // Validate implements the validator interface
-func (svc *Service) validate(datatypes ...datatype.T) error {
+func (svc *Service) validate(datatypes ...validator.Type) error {
 	// check method
 	err := svc.isMethodAvailable()
 	if err != nil {
@@ -195,7 +195,7 @@ func (svc *Service) isPatternValid() error {
 	return nil
 }
 
-func (svc *Service) validateInput(types []datatype.T) error {
+func (svc *Service) validateInput(types []validator.Type) error {
 
 	// ignore no parameter
 	if svc.Input == nil || len(svc.Input) < 1 {
@@ -285,7 +285,7 @@ func (svc *Service) validateInput(types []datatype.T) error {
 	return nil
 }
 
-func (svc *Service) validateOutput(types []datatype.T) error {
+func (svc *Service) validateOutput(types []validator.Type) error {
 
 	// ignore no parameter
 	if svc.Output == nil || len(svc.Output) < 1 {
diff --git a/internal/dynfunc/signature.go b/internal/dynfunc/signature.go
index 35783ab..d5c30aa 100644
--- a/internal/dynfunc/signature.go
+++ b/internal/dynfunc/signature.go
@@ -31,17 +31,17 @@ func BuildSignature(service config.Service) *Signature {
 		}
 		// make a pointer if optional
 		if param.Optional {
-			s.Input[param.Rename] = reflect.PtrTo(param.ExtractType)
+			s.Input[param.Rename] = reflect.PtrTo(param.GoType)
 			continue
 		}
-		s.Input[param.Rename] = param.ExtractType
+		s.Input[param.Rename] = param.GoType
 	}
 
 	for _, param := range service.Output {
 		if len(param.Rename) < 1 {
 			continue
 		}
-		s.Output[param.Rename] = param.ExtractType
+		s.Output[param.Rename] = param.GoType
 	}
 
 	return s
diff --git a/validator/any.go b/validator/any.go
new file mode 100644
index 0000000..c9b2ef0
--- /dev/null
+++ b/validator/any.go
@@ -0,0 +1,24 @@
+package validator
+
+import (
+	"reflect"
+)
+
+// AnyType makes the "any" type available in the aicra configuration
+// It considers valid any value
+type AnyType struct{}
+
+// GoType returns the interface{} type
+func (AnyType) GoType() reflect.Type {
+	return reflect.TypeOf(interface{}(nil))
+}
+
+// Validator that considers any value valid
+func (AnyType) Validator(typename string, avail ...Type) ValidateFunc {
+	if typename != "any" {
+		return nil
+	}
+	return func(value interface{}) (interface{}, bool) {
+		return value, true
+	}
+}
diff --git a/datatype/builtin/any_test.go b/validator/any_test.go
similarity index 84%
rename from datatype/builtin/any_test.go
rename to validator/any_test.go
index 8d9ae03..d612047 100644
--- a/datatype/builtin/any_test.go
+++ b/validator/any_test.go
@@ -1,16 +1,16 @@
-package builtin_test
+package validator_test
 
 import (
 	"fmt"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestAny_AvailableTypes(t *testing.T) {
 	t.Parallel()
 
-	dt := builtin.AnyDataType{}
+	dt := validator.AnyType{}
 
 	tests := []struct {
 		Type    string
@@ -26,7 +26,7 @@ func TestAny_AvailableTypes(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		validator := dt.Build(test.Type)
+		validator := dt.Validator(test.Type)
 
 		if validator == nil {
 			if test.Handled {
@@ -47,7 +47,7 @@ func TestAny_AlwaysTrue(t *testing.T) {
 
 	const typeName = "any"
 
-	validator := builtin.AnyDataType{}.Build(typeName)
+	validator := validator.AnyType{}.Validator(typeName)
 	if validator == nil {
 		t.Errorf("expect %q to be handled", typeName)
 		t.Fail()
diff --git a/datatype/builtin/bool.go b/validator/bool.go
similarity index 51%
rename from datatype/builtin/bool.go
rename to validator/bool.go
index 720c59d..9a93069 100644
--- a/datatype/builtin/bool.go
+++ b/validator/bool.go
@@ -1,23 +1,24 @@
-package builtin
+package validator
 
 import (
 	"reflect"
-
-	"github.com/xdrm-io/aicra/datatype"
 )
 
-// BoolDataType is what its name tells
-type BoolDataType struct{}
+// BoolType makes the "bool" type available in the aicra configuration
+// It considers valid:
+// - booleans
+// - strings containing "true" or "false"
+// - []byte containing "true" or "false"
+type BoolType struct{}
 
-// Type returns the type of data
-func (BoolDataType) Type() reflect.Type {
+// GoType returns the `bool` type
+func (BoolType) GoType() reflect.Type {
 	return reflect.TypeOf(true)
 }
 
-// Build returns the validator
-func (BoolDataType) Build(typeName string, registry ...datatype.T) datatype.Validator {
-	// nothing if type not handled
-	if typeName != "bool" {
+// Validator for bool values
+func (BoolType) Validator(typename string, avail ...Type) ValidateFunc {
+	if typename != "bool" {
 		return nil
 	}
 
diff --git a/datatype/builtin/bool_test.go b/validator/bool_test.go
similarity index 88%
rename from datatype/builtin/bool_test.go
rename to validator/bool_test.go
index c44b262..8600d34 100644
--- a/datatype/builtin/bool_test.go
+++ b/validator/bool_test.go
@@ -1,16 +1,16 @@
-package builtin_test
+package validator_test
 
 import (
 	"fmt"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestBool_AvailableTypes(t *testing.T) {
 	t.Parallel()
 
-	dt := builtin.BoolDataType{}
+	dt := validator.BoolType{}
 
 	tests := []struct {
 		Type    string
@@ -26,7 +26,7 @@ func TestBool_AvailableTypes(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.Type, func(t *testing.T) {
-			validator := dt.Build(test.Type)
+			validator := dt.Validator(test.Type)
 			if validator == nil {
 				if test.Handled {
 					t.Errorf("expect %q to be handled", test.Type)
@@ -49,7 +49,7 @@ func TestBool_Values(t *testing.T) {
 
 	const typeName = "bool"
 
-	validator := builtin.BoolDataType{}.Build(typeName)
+	validator := validator.BoolType{}.Validator(typeName)
 	if validator == nil {
 		t.Errorf("expect %q to be handled", typeName)
 		t.Fail()
diff --git a/datatype/builtin/float.go b/validator/float.go
similarity index 52%
rename from datatype/builtin/float.go
rename to validator/float.go
index 6bb39f9..b6d7e53 100644
--- a/datatype/builtin/float.go
+++ b/validator/float.go
@@ -1,24 +1,27 @@
-package builtin
+package validator
 
 import (
 	"encoding/json"
 	"reflect"
-
-	"github.com/xdrm-io/aicra/datatype"
 )
 
-// FloatDataType is what its name tells
-type FloatDataType struct{}
+// FloatType makes the "float" (or "float64") type available in the aicra configuration
+// It considers valid:
+// - float64
+// - int (since it does not overflow)
+// - uint (since it does not overflow)
+// - strings containing json-compatible floats
+// - []byte containing json-compatible floats
+type FloatType struct{}
 
-// Type returns the type of data
-func (FloatDataType) Type() reflect.Type {
+// GoType returns the `float64` type
+func (FloatType) GoType() reflect.Type {
 	return reflect.TypeOf(float64(0))
 }
 
-// Build returns the validator
-func (FloatDataType) Build(typeName string, registry ...datatype.T) datatype.Validator {
-	// nothing if type not handled
-	if typeName != "float64" && typeName != "float" {
+// Validator for float64 values
+func (FloatType) Validator(typename string, avail ...Type) ValidateFunc {
+	if typename != "float64" && typename != "float" {
 		return nil
 	}
 	return func(value interface{}) (interface{}, bool) {
diff --git a/datatype/builtin/float_test.go b/validator/float_test.go
similarity index 91%
rename from datatype/builtin/float_test.go
rename to validator/float_test.go
index 193dd7c..b965441 100644
--- a/datatype/builtin/float_test.go
+++ b/validator/float_test.go
@@ -1,17 +1,17 @@
-package builtin_test
+package validator_test
 
 import (
 	"fmt"
 	"math"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestFloat64_AvailableTypes(t *testing.T) {
 	t.Parallel()
 
-	dt := builtin.FloatDataType{}
+	dt := validator.FloatType{}
 
 	tests := []struct {
 		Type    string
@@ -33,7 +33,7 @@ func TestFloat64_AvailableTypes(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.Type, func(t *testing.T) {
-			validator := dt.Build(test.Type)
+			validator := dt.Validator(test.Type)
 			if validator == nil {
 				if test.Handled {
 					t.Errorf("expect %q to be handled", test.Type)
@@ -56,7 +56,7 @@ func TestFloat64_Values(t *testing.T) {
 
 	const typeName = "float"
 
-	validator := builtin.FloatDataType{}.Build(typeName)
+	validator := validator.FloatType{}.Validator(typeName)
 	if validator == nil {
 		t.Errorf("expect %q to be handled", typeName)
 		t.Fail()
diff --git a/datatype/builtin/int.go b/validator/int.go
similarity index 63%
rename from datatype/builtin/int.go
rename to validator/int.go
index b1473a6..d7ec83c 100644
--- a/datatype/builtin/int.go
+++ b/validator/int.go
@@ -1,25 +1,29 @@
-package builtin
+package validator
 
 import (
 	"encoding/json"
 	"math"
 	"reflect"
-
-	"github.com/xdrm-io/aicra/datatype"
 )
 
-// IntDataType is what its name tells
-type IntDataType struct{}
+// IntType makes the "int" type available in the aicra configuration
+// It considers valid:
+// - int
+// - float64 (since it does not overflow)
+// - uint (since it does not overflow)
+// - strings containing json-compatible integers
+// - []byte containing json-compatible integers
+type IntType struct{}
 
-// Type returns the type of data
-func (IntDataType) Type() reflect.Type {
+// GoType returns the `int` type
+func (IntType) GoType() reflect.Type {
 	return reflect.TypeOf(int(0))
 }
 
-// Build returns the validator
-func (IntDataType) Build(typeName string, registry ...datatype.T) datatype.Validator {
+// Validator for int values
+func (IntType) Validator(typename string, avail ...Type) ValidateFunc {
 	// nothing if type not handled
-	if typeName != "int" {
+	if typename != "int" {
 		return nil
 	}
 
diff --git a/datatype/builtin/int_test.go b/validator/int_test.go
similarity index 91%
rename from datatype/builtin/int_test.go
rename to validator/int_test.go
index 8b7a157..14dc515 100644
--- a/datatype/builtin/int_test.go
+++ b/validator/int_test.go
@@ -1,17 +1,17 @@
-package builtin_test
+package validator_test
 
 import (
 	"fmt"
 	"math"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestInt_AvailableTypes(t *testing.T) {
 	t.Parallel()
 
-	dt := builtin.IntDataType{}
+	dt := validator.IntType{}
 
 	tests := []struct {
 		Type    string
@@ -27,7 +27,7 @@ func TestInt_AvailableTypes(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.Type, func(t *testing.T) {
-			validator := dt.Build(test.Type)
+			validator := dt.Validator(test.Type)
 			if validator == nil {
 				if test.Handled {
 					t.Errorf("expect %q to be handled", test.Type)
@@ -50,7 +50,7 @@ func TestInt_Values(t *testing.T) {
 
 	const typeName = "int"
 
-	validator := builtin.IntDataType{}.Build(typeName)
+	validator := validator.IntType{}.Validator(typeName)
 	if validator == nil {
 		t.Errorf("expect %q to be handled", typeName)
 		t.Fail()
diff --git a/datatype/builtin/string.go b/validator/string.go
similarity index 63%
rename from datatype/builtin/string.go
rename to validator/string.go
index 902daf7..307c7cd 100644
--- a/datatype/builtin/string.go
+++ b/validator/string.go
@@ -1,32 +1,37 @@
-package builtin
+package validator
 
 import (
 	"reflect"
 	"regexp"
 	"strconv"
-
-	"github.com/xdrm-io/aicra/datatype"
 )
 
-var fixedLengthRegex = regexp.MustCompile(`^string\((\d+)\)$`)
-var variableLengthRegex = regexp.MustCompile(`^string\((\d+), ?(\d+)\)$`)
+var (
+	fixedLengthRegex    = regexp.MustCompile(`^string\((\d+)\)$`)
+	variableLengthRegex = regexp.MustCompile(`^string\((\d+), ?(\d+)\)$`)
+)
 
-// StringDataType is what its name tells
-type StringDataType struct{}
+// StringType makes the types beloz available in the aicra configuration:
+// - "string" considers any string valid
+// - "string(n)" considers any string with an exact size of `n` valid
+// - "string(a,b)" considers any string with a size between `a` and `b` valid
+// > for the last one, `a` and `b` are included in the valid sizes
+type StringType struct{}
 
-// Type returns the type of data
-func (StringDataType) Type() reflect.Type {
+// GoType returns the `string` type
+func (StringType) GoType() reflect.Type {
 	return reflect.TypeOf(string(""))
 }
 
-// Build returns the validator.
-// availables type names are : `string`, `string(length)` and `string(minLength, maxLength)`.
-func (s StringDataType) Build(typeName string, registry ...datatype.T) datatype.Validator {
-	simple := typeName == "string"
-	fixedLengthMatches := fixedLengthRegex.FindStringSubmatch(typeName)
-	variableLengthMatches := variableLengthRegex.FindStringSubmatch(typeName)
+// Validator for strings with any/fixed/bound sizes
+func (s StringType) Validator(typename string, avail ...Type) ValidateFunc {
+	var (
+		simple                = (typename == "string")
+		fixedLengthMatches    = fixedLengthRegex.FindStringSubmatch(typename)
+		variableLengthMatches = variableLengthRegex.FindStringSubmatch(typename)
+	)
 
-	// nothing if type not handled
+	// ignore unknown typename
 	if !simple && fixedLengthMatches == nil && variableLengthMatches == nil {
 		return nil
 	}
@@ -40,7 +45,7 @@ func (s StringDataType) Build(typeName string, registry ...datatype.T) datatype.
 	if fixedLengthMatches != nil {
 		exLen, ok := s.getFixedLength(fixedLengthMatches)
 		if !ok {
-			mustFail = true
+			return nil
 		}
 		min = exLen
 		max = exLen
@@ -49,7 +54,7 @@ func (s StringDataType) Build(typeName string, registry ...datatype.T) datatype.
 	} else if variableLengthMatches != nil {
 		exMin, exMax, ok := s.getVariableLength(variableLengthMatches)
 		if !ok {
-			mustFail = true
+			return nil
 		}
 		min = exMin
 		max = exMax
@@ -84,7 +89,7 @@ func (s StringDataType) Build(typeName string, registry ...datatype.T) datatype.
 }
 
 // getFixedLength returns the fixed length from regex matches and a success state.
-func (StringDataType) getFixedLength(regexMatches []string) (int, bool) {
+func (StringType) getFixedLength(regexMatches []string) (int, bool) {
 	// incoherence error
 	if regexMatches == nil || len(regexMatches) < 2 {
 		return 0, false
@@ -100,7 +105,7 @@ func (StringDataType) getFixedLength(regexMatches []string) (int, bool) {
 }
 
 // getVariableLength returns the length min and max from regex matches and a success state.
-func (StringDataType) getVariableLength(regexMatches []string) (int, int, bool) {
+func (StringType) getVariableLength(regexMatches []string) (int, int, bool) {
 	// incoherence error
 	if regexMatches == nil || len(regexMatches) < 3 {
 		return 0, 0, false
diff --git a/datatype/builtin/string_test.go b/validator/string_test.go
similarity index 93%
rename from datatype/builtin/string_test.go
rename to validator/string_test.go
index 4441525..0a038ef 100644
--- a/datatype/builtin/string_test.go
+++ b/validator/string_test.go
@@ -1,16 +1,16 @@
-package builtin_test
+package validator_test
 
 import (
 	"fmt"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestString_AvailableTypes(t *testing.T) {
 	t.Parallel()
 
-	dt := builtin.StringDataType{}
+	dt := validator.StringType{}
 
 	tests := []struct {
 		Type    string
@@ -53,7 +53,7 @@ func TestString_AvailableTypes(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.Type, func(t *testing.T) {
-			validator := dt.Build(test.Type)
+			validator := dt.Validator(test.Type)
 
 			if validator == nil {
 				if test.Handled {
@@ -75,7 +75,7 @@ func TestString_AnyLength(t *testing.T) {
 
 	const typeName = "string"
 
-	validator := builtin.StringDataType{}.Build(typeName)
+	validator := validator.StringType{}.Validator(typeName)
 	if validator == nil {
 		t.Errorf("expect %q to be handled", typeName)
 		t.Fail()
@@ -133,7 +133,7 @@ func TestString_FixedLength(t *testing.T) {
 
 	for i, test := range tests {
 		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
-			validator := builtin.StringDataType{}.Build(test.Type)
+			validator := validator.StringType{}.Validator(test.Type)
 			if validator == nil {
 				t.Errorf("expect %q to be handled", test.Type)
 				t.Fail()
@@ -194,7 +194,7 @@ func TestString_VariableLength(t *testing.T) {
 
 	for i, test := range tests {
 		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
-			validator := builtin.StringDataType{}.Build(test.Type)
+			validator := validator.StringType{}.Validator(test.Type)
 			if validator == nil {
 				t.Errorf("expect %q to be handled", test.Type)
 				t.Fail()
diff --git a/datatype/builtin/uint.go b/validator/uint.go
similarity index 65%
rename from datatype/builtin/uint.go
rename to validator/uint.go
index 990d15b..0df72f4 100644
--- a/datatype/builtin/uint.go
+++ b/validator/uint.go
@@ -1,25 +1,28 @@
-package builtin
+package validator
 
 import (
 	"encoding/json"
 	"math"
 	"reflect"
-
-	"github.com/xdrm-io/aicra/datatype"
 )
 
-// UintDataType is what its name tells
-type UintDataType struct{}
+// UintType makes the "uint" type available in the aicra configuration
+// It considers valid:
+// - uint
+// - int (since it does not overflow)
+// - float64 (since it does not overflow)
+// - strings containing json-compatible integers
+// - []byte containing json-compatible integers
+type UintType struct{}
 
-// Type returns the type of data
-func (UintDataType) Type() reflect.Type {
+// GoType returns the `uint` type
+func (UintType) GoType() reflect.Type {
 	return reflect.TypeOf(uint(0))
 }
 
-// Build returns the validator
-func (UintDataType) Build(typeName string, registry ...datatype.T) datatype.Validator {
-	// nothing if type not handled
-	if typeName != "uint" {
+// Validator for uint values
+func (UintType) Validator(other string, avail ...Type) ValidateFunc {
+	if other != "uint" {
 		return nil
 	}
 
diff --git a/datatype/builtin/uint_test.go b/validator/uint_test.go
similarity index 92%
rename from datatype/builtin/uint_test.go
rename to validator/uint_test.go
index 6175321..4fc9be9 100644
--- a/datatype/builtin/uint_test.go
+++ b/validator/uint_test.go
@@ -1,17 +1,17 @@
-package builtin_test
+package validator_test
 
 import (
 	"fmt"
 	"math"
 	"testing"
 
-	"github.com/xdrm-io/aicra/datatype/builtin"
+	"github.com/xdrm-io/aicra/validator"
 )
 
 func TestUint_AvailableTypes(t *testing.T) {
 	t.Parallel()
 
-	dt := builtin.UintDataType{}
+	dt := validator.UintType{}
 
 	tests := []struct {
 		Type    string
@@ -27,7 +27,7 @@ func TestUint_AvailableTypes(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.Type, func(t *testing.T) {
-			validator := dt.Build(test.Type)
+			validator := dt.Validator(test.Type)
 			if validator == nil {
 				if test.Handled {
 					t.Errorf("expect %q to be handled", test.Type)
@@ -50,7 +50,7 @@ func TestUint_Values(t *testing.T) {
 
 	const typeName = "uint"
 
-	validator := builtin.UintDataType{}.Build(typeName)
+	validator := validator.UintType{}.Validator(typeName)
 	if validator == nil {
 		t.Errorf("expect %q to be handled", typeName)
 		t.Fail()
diff --git a/validator/validator.go b/validator/validator.go
new file mode 100644
index 0000000..fa3d389
--- /dev/null
+++ b/validator/validator.go
@@ -0,0 +1,55 @@
+package validator
+
+import (
+	"reflect"
+)
+
+// ValidateFunc returns whether a given value fulfills the datatype and casts
+// the value into a go type.
+//
+// for example, if a validator checks for upper case strings, whether the value
+// is a []byte, a string or a []rune, if the value matches is all upper-case, it
+// will be cast into a go type, say, string.
+type ValidateFunc func(value interface{}) (cast interface{}, valid bool)
+
+// Type defines an available in/out parameter "type" for the aicra configuration
+//
+// A Type maps to a go type in order to generate the handler signature from the
+// aicra configuration
+//
+// A Type returns a custom validator when the typename matches
+type Type interface {
+	// Validator function when the typename matches. It must return nil when the
+	// typename does not match
+	//
+	// The `typename` argument has to match types used in your aicra configuration
+	// in parameter definitions ("in", "out") and in the "type" json field.
+	//
+	// basic example:
+	// - `IntType.Validator("string")`` should return nil
+	// - `IntType.Validator("int")`` should return its ValidateFunc
+	//
+	// The `typename` is not returned by a simple method i.e. `TypeName() string`
+	// because it allows for validation relative to the typename, for instance:
+	// - `VarcharType.Validator("varchar")` valides any string
+	// - `VarcharType.Validator("varchar(2)")` validates any string of 2
+	//   characters
+	// - `VarcharType.Validator("varchar(1,3)")` validates any string
+	//   with a length between 1 and 3
+	//
+	// The `avail` argument represents all other available Types. It allows a
+	// Type to use other available Types internally.
+	//
+	// recursive example: slices
+	// - `SliceType.Validator("[]int", avail...)` validates a slice containing
+	//   values that are valide to the `IntType`
+	// - `SliceType.Validator("[]varchar", avail...)` validates a slice containing
+	//   values that are valid to the `VarcharType`
+	//
+	// and so on.. this works for maps, structs, etc
+	Validator(typename string, avail ...Type) ValidateFunc
+
+	// GoType must return the go type associated with the output type of ValidateFunc.
+	// It is used to define handlers' signature from the configuration file.
+	GoType() reflect.Type
+}