diff --git a/src/FAST-Core-Tools/FASTAbstractDifferentialValidator.class.st b/src/FAST-Core-Tools/FASTAbstractDifferentialValidator.class.st
new file mode 100644
index 0000000..d232a12
--- /dev/null
+++ b/src/FAST-Core-Tools/FASTAbstractDifferentialValidator.class.st
@@ -0,0 +1,101 @@
+"
+I help checking the completness of FAST meta-model
+
+## Process
+
+For this:
+- I go through all source files in a file hierarchy
+- I extract a FAST model for each source file
+- I re-export the source code from the FAST model
+- I extract a new FAST model from the new code, and
+- finally I compare the 2 FAST models (they should be the same)
+
+## Caveat
+
+This is not full-proof
+- Some ASTs can be different and the code be ""the same"" for example `a + b + c` usually has different AST from `a + (b + c)`
+- properties of nodes are currently not tested, so `a==b` is considered equal to `a!=b` because the #operator is not tested
+
+## Configuration
+
+There is a setting strict/not-strict (not by default) that allows to accept some minor AST differences (see above)
+For this, a suitable `acceptableAST:differentFrom:` method should be defined that will receive 2 differeing nodes (one in each AST) and  must decide whether the difference is acceptable
+
+There is a `skipPaths` list to allow skiping some paths in the main file directory
+"
+Class {
+	#name : #FASTAbstractDifferentialValidator,
+	#superclass : #FASTAbstractValidator,
+	#instVars : [
+		'comparator'
+	],
+	#category : #'FAST-Core-Tools-Validator'
+}
+
+{ #category : #accessing }
+FASTAbstractDifferentialValidator >> comparator [
+
+	^comparator ifNil: [ comparator := self comparatorClass new ]
+]
+
+{ #category : #accessing }
+FASTAbstractDifferentialValidator >> comparatorClass [
+
+	^FamixModelComparator
+]
+
+{ #category : #running }
+FASTAbstractDifferentialValidator >> compare: node1 to: node2 [
+	
+	self comparator compare: node1 to: node2
+]
+
+{ #category : #utilities }
+FASTAbstractDifferentialValidator >> getASTFromFileReference: aFileReference [
+
+	^self getTopLevelNodes: (super getASTFromFileReference: aFileReference)
+]
+
+{ #category : #utilities }
+FASTAbstractDifferentialValidator >> getRootNode: aModel [
+
+	^aModel detect: [ : e | e allParents isEmpty ]
+]
+
+{ #category : #utilities }
+FASTAbstractDifferentialValidator >> getTopLevelNodes: model [
+
+	self subclassResponsibility
+]
+
+{ #category : #utilities }
+FASTAbstractDifferentialValidator >> reExportAST: ast [
+
+	self subclassResponsibility
+]
+
+{ #category : #running }
+FASTAbstractDifferentialValidator >> runOnSourceFile: aFileReference [
+
+	| astOrig astBis topLevelNodes |
+	aFileReference fullName traceCr.
+
+	topLevelNodes := [
+		self getASTFromFileReference: aFileReference
+	]
+	on: Error
+	do: [
+		'  ** NOT PARSEABLE **' traceCr.
+		"Note: If we cannot get the original AST, no use to try to regenerate it"
+		#()
+	].
+
+	topLevelNodes ifNotEmpty: [
+		
+		astOrig := self getRootNode: topLevelNodes.
+		astBis := self getRootNode:
+			(self getASTFromString: (self reExportAST: astOrig)).
+	
+		self compare: astOrig to: astBis
+	]
+]
diff --git a/src/FAST-Core-Tools/FASTAbstractValidator.class.st b/src/FAST-Core-Tools/FASTAbstractValidator.class.st
new file mode 100644
index 0000000..38ea112
--- /dev/null
+++ b/src/FAST-Core-Tools/FASTAbstractValidator.class.st
@@ -0,0 +1,103 @@
+Class {
+	#name : #FASTAbstractValidator,
+	#superclass : #Object,
+	#instVars : [
+		'skipPaths',
+		'encoding'
+	],
+	#category : #'FAST-Core-Tools-Validator'
+}
+
+{ #category : #accessing }
+FASTAbstractValidator >> defaultEncoding [
+	"other possibilities are 'latin1', 'utf8', ...
+	see `ZnCharacterEncoder knownEncodingIdentifiers` for all possibilities"
+	^encoding ifNil: [ 'iso-8859-1' ]
+]
+
+{ #category : #accessing }
+FASTAbstractValidator >> encoding [
+
+	^encoding
+]
+
+{ #category : #accessing }
+FASTAbstractValidator >> encoding: aString [
+
+	encoding := aString
+]
+
+{ #category : #utilities }
+FASTAbstractValidator >> getASTFromFileReference: aFileReference [
+
+	^aFileReference readStreamEncoded: self defaultEncoding do: [ :stream |
+		self getASTFromString: stream contents ]
+
+]
+
+{ #category : #utilities }
+FASTAbstractValidator >> getASTFromString: stream [
+
+	self subclassResponsibility  
+]
+
+{ #category : #initialization }
+FASTAbstractValidator >> initialize [
+
+	super initialize.
+
+	skipPaths := #().
+]
+
+{ #category : #testing }
+FASTAbstractValidator >> isSourceFile: aFileReference [
+
+	self subclassResponsibility 
+]
+
+{ #category : #'instance creation' }
+FASTAbstractValidator >> on: aDirectoryName [
+
+	self runOnFileReference: aDirectoryName asFileReference
+]
+
+{ #category : #running }
+FASTAbstractValidator >> runOnDirectory: aDirectory [
+
+	aDirectory isDirectory
+		ifFalse: [ Exception signal: aDirectory fullName , ' not a directory' ].
+
+	aDirectory children do: [ :fileRef | self runOnFileReference: fileRef ]
+]
+
+{ #category : #running }
+FASTAbstractValidator >> runOnFileReference: aFileReference [
+
+	(self skipPaths includes: aFileReference fullName)
+		ifTrue: [ ^self ].
+
+	aFileReference isDirectory
+		ifTrue: [ ^self runOnDirectory: aFileReference ].
+
+	(self isSourceFile: aFileReference)
+		ifTrue: [ ^self runOnSourceFile: aFileReference ].
+
+]
+
+{ #category : #testing }
+FASTAbstractValidator >> runOnSourceFile: aFileReference [
+
+	self subclassResponsibility 
+]
+
+{ #category : #accessing }
+FASTAbstractValidator >> skipPaths [
+
+	^ skipPaths
+]
+
+{ #category : #accessing }
+FASTAbstractValidator >> skipPaths: anObject [
+
+	skipPaths := anObject
+]