diff --git a/manual tests/7 vala composite widgets/mywidget.vala b/manual tests/7 vala composite widgets/mywidget.vala
index 09a2064ca..68eaecc27 100644
--- a/manual tests/7 vala composite widgets/mywidget.vala	
+++ b/manual tests/7 vala composite widgets/mywidget.vala	
@@ -2,40 +2,40 @@ using Gtk;
 
 [GtkTemplate (ui = "/org/foo/my/mywidget.ui")]
 public class MyWidget : Box {
-	public string text {
-		get { return entry.text; }
-		set { entry.text = value; }
-	}
+    public string text {
+        get { return entry.text; }
+        set { entry.text = value; }
+    }
 
-	[GtkChild]
-	private Entry entry;
+    [GtkChild]
+    private Entry entry;
 
-	public MyWidget (string text) {
-		this.text = text;
-	}
+    public MyWidget (string text) {
+        this.text = text;
+    }
 
-	[GtkCallback]
-	private void on_button_clicked (Button button) {
-		print ("The button was clicked with entry text: %s\n", entry.text);
-	}
+    [GtkCallback]
+    private void on_button_clicked (Button button) {
+        print ("The button was clicked with entry text: %s\n", entry.text);
+    }
 
-	[GtkCallback]
-	private void on_entry_changed (Editable editable) {
-		print ("The entry text changed: %s\n", entry.text);
+    [GtkCallback]
+    private void on_entry_changed (Editable editable) {
+        print ("The entry text changed: %s\n", entry.text);
 
-		notify_property ("text");
-	}
+        notify_property ("text");
+    }
 }
 
 void main(string[] args) {
-	Gtk.init (ref args);
-	var win = new Window();
-	win.destroy.connect (Gtk.main_quit);
+    Gtk.init (ref args);
+    var win = new Window();
+    win.destroy.connect (Gtk.main_quit);
 
-	var widget = new MyWidget ("The entry text!");
+    var widget = new MyWidget ("The entry text!");
 
-	win.add (widget);
-	win.show_all ();
+    win.add (widget);
+    win.show_all ();
 
-	Gtk.main ();
+    Gtk.main ();
 }
diff --git a/run_project_tests.py b/run_project_tests.py
index 1385a78af..e390aaf86 100755
--- a/run_project_tests.py
+++ b/run_project_tests.py
@@ -636,10 +636,32 @@ def check_file(fname):
         linenum += 1
 
 def check_format():
+    check_suffixes = {'.c',
+                      '.cpp',
+                      '.cxx',
+                      '.cc',
+                      '.rs',
+                      '.f90',
+                      '.vala',
+                      '.d',
+                      '.s',
+                      '.m',
+                      '.mm',
+                      '.asm',
+                      '.java',
+                      '.txt',
+                      '.py',
+                      '.swift',
+                      '.build',
+                      }
     for (root, _, files) in os.walk('.'):
-        for file in files:
-            if file.endswith('.py') or file.endswith('.build') or file == 'meson_options.txt':
-                fullname = os.path.join(root, file)
+        if '.dub' in root: # external deps are here
+            continue
+        for fname in files:
+            if os.path.splitext(fname)[1].lower() in check_suffixes:
+                if os.path.split(fname)[1] == 'sitemap.txt':
+                    continue
+                fullname = os.path.join(root, fname)
                 check_file(fullname)
 
 def check_meson_commands_work():
diff --git a/test cases/common/106 subproject subdir/prog.c b/test cases/common/106 subproject subdir/prog.c
index 02ae3372d..cf6f42548 100644
--- a/test cases/common/106 subproject subdir/prog.c	
+++ b/test cases/common/106 subproject subdir/prog.c	
@@ -1,5 +1,5 @@
 #include <sub.h>
 
 int main() {
-	return sub();
+    return sub();
 }
diff --git a/test cases/common/106 subproject subdir/subprojects/sub/lib/sub.c b/test cases/common/106 subproject subdir/subprojects/sub/lib/sub.c
index 3291e3cb1..068a5b89c 100644
--- a/test cases/common/106 subproject subdir/subprojects/sub/lib/sub.c	
+++ b/test cases/common/106 subproject subdir/subprojects/sub/lib/sub.c	
@@ -1,5 +1,5 @@
 #include "sub.h"
 
 int sub() {
-	return 0;
+    return 0;
 }
diff --git a/test cases/common/120 subdir subproject/prog/prog.c b/test cases/common/120 subdir subproject/prog/prog.c
index 02ae3372d..cf6f42548 100644
--- a/test cases/common/120 subdir subproject/prog/prog.c	
+++ b/test cases/common/120 subdir subproject/prog/prog.c	
@@ -1,5 +1,5 @@
 #include <sub.h>
 
 int main() {
-	return sub();
+    return sub();
 }
diff --git a/test cases/common/120 subdir subproject/subprojects/sub/sub.c b/test cases/common/120 subdir subproject/subprojects/sub/sub.c
index 3291e3cb1..068a5b89c 100644
--- a/test cases/common/120 subdir subproject/subprojects/sub/sub.c	
+++ b/test cases/common/120 subdir subproject/subprojects/sub/sub.c	
@@ -1,5 +1,5 @@
 #include "sub.h"
 
 int sub() {
-	return 0;
+    return 0;
 }
diff --git a/test cases/common/124 test skip/test_skip.c b/test cases/common/124 test skip/test_skip.c
index d050a610b..db26681e1 100644
--- a/test cases/common/124 test skip/test_skip.c	
+++ b/test cases/common/124 test skip/test_skip.c	
@@ -1,4 +1,3 @@
-int main(int argc, char *argv[])
-{
-	return 77;
+int main(int argc, char *argv[]) {
+    return 77;
 }
diff --git a/test cases/common/126 llvm ir and assembly/square-arm.S b/test cases/common/126 llvm ir and assembly/square-arm.S
index e66fa4790..4dd446753 100644
--- a/test cases/common/126 llvm ir and assembly/square-arm.S	
+++ b/test cases/common/126 llvm ir and assembly/square-arm.S	
@@ -7,6 +7,6 @@
 #endif
 
 SYMBOL_NAME(square_unsigned):
-	mul	r1, r0, r0
-	mov	r0, r1
-	mov	pc, lr
+    mul r1, r0, r0
+    mov r0, r1
+    mov pc, lr
diff --git a/test cases/common/126 llvm ir and assembly/square-x86.S b/test cases/common/126 llvm ir and assembly/square-x86.S
index 7d1202a76..18284c1a6 100644
--- a/test cases/common/126 llvm ir and assembly/square-x86.S	
+++ b/test cases/common/126 llvm ir and assembly/square-x86.S	
@@ -11,9 +11,10 @@ PUBLIC square_unsigned
 _TEXT   SEGMENT
 
 square_unsigned PROC var1:DWORD
-        mov     eax, var1
-	imul	eax, eax
-	ret
+    mov     eax, var1
+    imul eax, eax
+    ret
+
 square_unsigned ENDP
 
 _TEXT   ENDS
@@ -28,8 +29,8 @@ END
 #endif
 
 SYMBOL_NAME(square_unsigned):
-	movl	4(%esp), %eax
-	imull	%eax, %eax
-	retl
+    movl 4(%esp), %eax
+    imull %eax, %eax
+    retl
 
 #endif
diff --git a/test cases/common/126 llvm ir and assembly/square-x86_64.S b/test cases/common/126 llvm ir and assembly/square-x86_64.S
index 09cc7a4d0..5678d00a3 100644
--- a/test cases/common/126 llvm ir and assembly/square-x86_64.S	
+++ b/test cases/common/126 llvm ir and assembly/square-x86_64.S	
@@ -7,8 +7,8 @@ _TEXT   SEGMENT
 
 SYMBOL_NAME(square_unsigned) PROC
         mov     eax, ecx
-	imul	eax, eax
-	ret
+    imul eax, eax
+    ret
 SYMBOL_NAME(square_unsigned) ENDP
 
 _TEXT   ENDS
@@ -24,14 +24,14 @@ END
 
 # if defined(_WIN32) || defined(__CYGWIN__) /* msabi */
 SYMBOL_NAME(square_unsigned):
-	imull	%ecx, %ecx
-	movl	%ecx, %eax
-	retq
+    imull %ecx, %ecx
+    movl %ecx, %eax
+    retq
 # else /* sysvabi */
 SYMBOL_NAME(square_unsigned):
-	imull	%edi, %edi
-	movl	%edi, %eax
-	retq
+    imull %edi, %edi
+    movl %edi, %eax
+    retq
 # endif
 
 #endif
diff --git a/test cases/common/84 extract from nested subdir/src/first/lib_first.c b/test cases/common/84 extract from nested subdir/src/first/lib_first.c
index 01e06b62f..30049063f 100644
--- a/test cases/common/84 extract from nested subdir/src/first/lib_first.c	
+++ b/test cases/common/84 extract from nested subdir/src/first/lib_first.c	
@@ -1,3 +1,3 @@
 int first() {
-	return 1001;
+    return 1001;
 }
diff --git a/test cases/common/84 extract from nested subdir/tst/first/exe_first.c b/test cases/common/84 extract from nested subdir/tst/first/exe_first.c
index 4f714df2c..f6c1f7471 100644
--- a/test cases/common/84 extract from nested subdir/tst/first/exe_first.c	
+++ b/test cases/common/84 extract from nested subdir/tst/first/exe_first.c	
@@ -1,5 +1,5 @@
 int first(void);
 
 int main() {
-	return first() - 1001;
+    return first() - 1001;
 }
diff --git a/test cases/frameworks/4 qt/manualinclude.cpp b/test cases/frameworks/4 qt/manualinclude.cpp
index 6c1ac2f1c..2682dd9d2 100644
--- a/test cases/frameworks/4 qt/manualinclude.cpp	
+++ b/test cases/frameworks/4 qt/manualinclude.cpp	
@@ -7,7 +7,7 @@ ManualInclude::ManualInclude() {
 }
 
 void ManualInclude::myslot(void) {
-	;
+    ;
 }
 
 class MocClass : public QObject {
diff --git a/test cases/nasm/1 configure file/hello.asm b/test cases/nasm/1 configure file/hello.asm
index 4188b8dfe..bf4bf9688 100644
--- a/test cases/nasm/1 configure file/hello.asm	
+++ b/test cases/nasm/1 configure file/hello.asm	
@@ -1,27 +1,27 @@
 ;  hello.asm  a first program for nasm for Linux, Intel, gcc
 ;
-; assemble:	nasm -f elf -l hello.lst  hello.asm
-; link:		gcc -o hello  hello.o
-; run:	        hello
-; output is:	Hello World
+; assemble:    nasm -f elf -l hello.lst  hello.asm
+; link:        gcc -o hello  hello.o
+; run:            hello
+; output is:    Hello World
 
 %include "config.asm"
 
-	SECTION .data		; data section
-msg:	db "Hello World",10	; the string to print, 10=cr
-len:	equ $-msg		; "$" means "here"
-				; len is a value, not an address
+    SECTION .data        ; data section
+msg:    db "Hello World",10    ; the string to print, 10=cr
+len:    equ $-msg        ; "$" means "here"
+                ; len is a value, not an address
 
-	SECTION .text		; code section
-        global main		; make label available to linker
-main:				; standard  gcc  entry point
+    SECTION .text        ; code section
+        global main        ; make label available to linker
+main:                ; standard  gcc  entry point
 
-	mov	edx,len		; arg3, length of string to print
-	mov	ecx,msg		; arg2, pointer to string
-	mov	ebx,1		; arg1, where to write, screen
-	mov	eax,4		; write sysout command to int 80 hex
-	int	0x80		; interrupt 80 hex, call kernel
+    mov    edx,len        ; arg3, length of string to print
+    mov    ecx,msg        ; arg2, pointer to string
+    mov    ebx,1        ; arg1, where to write, screen
+    mov    eax,4        ; write sysout command to int 80 hex
+    int    0x80        ; interrupt 80 hex, call kernel
 
-	mov	ebx,HELLO	; exit code, 0=normal
-	mov	eax,1		; exit command to kernel
-	int	0x80		; interrupt 80 hex, call kernel
+    mov    ebx,HELLO    ; exit code, 0=normal
+    mov    eax,1        ; exit command to kernel
+    int    0x80        ; interrupt 80 hex, call kernel
diff --git a/test cases/unit/14 testsetup selection/main.c b/test cases/unit/14 testsetup selection/main.c
index cb3f7482f..33c14ce1d 100644
--- a/test cases/unit/14 testsetup selection/main.c	
+++ b/test cases/unit/14 testsetup selection/main.c	
@@ -1,3 +1,3 @@
 int main() {
-	return 0;
+    return 0;
 }
diff --git a/test cases/unit/14 testsetup selection/subprojects/bar/bar.c b/test cases/unit/14 testsetup selection/subprojects/bar/bar.c
index cb3f7482f..33c14ce1d 100644
--- a/test cases/unit/14 testsetup selection/subprojects/bar/bar.c	
+++ b/test cases/unit/14 testsetup selection/subprojects/bar/bar.c	
@@ -1,3 +1,3 @@
 int main() {
-	return 0;
+    return 0;
 }
diff --git a/test cases/unit/14 testsetup selection/subprojects/foo/foo.c b/test cases/unit/14 testsetup selection/subprojects/foo/foo.c
index cb3f7482f..33c14ce1d 100644
--- a/test cases/unit/14 testsetup selection/subprojects/foo/foo.c	
+++ b/test cases/unit/14 testsetup selection/subprojects/foo/foo.c	
@@ -1,3 +1,3 @@
 int main() {
-	return 0;
+    return 0;
 }
diff --git a/test cases/vala/10 mixed sources/vala/bar.vala b/test cases/vala/10 mixed sources/vala/bar.vala
index 10dce1ee9..0772f3edc 100644
--- a/test cases/vala/10 mixed sources/vala/bar.vala	
+++ b/test cases/vala/10 mixed sources/vala/bar.vala	
@@ -1,5 +1,5 @@
 extern int test ();
 
 public int main (string[] args) {
-	return test ();
+    return test ();
 }
diff --git a/test cases/vala/5 target glib/GLib.Thread.vala b/test cases/vala/5 target glib/GLib.Thread.vala
index a1a0414cd..701882180 100644
--- a/test cases/vala/5 target glib/GLib.Thread.vala	
+++ b/test cases/vala/5 target glib/GLib.Thread.vala	
@@ -1,43 +1,43 @@
 extern int get_ret_code ();
 
 public class MyThread : Object {
-	public int x_times { get; private set; }
-
-	public MyThread (int times) {
-		this.x_times = times;
-	}
-
-	public int run () {
-		for (int i = 0; i < this.x_times; i++) {
-			stdout.printf ("ping! %d/%d\n", i + 1, this.x_times);
-			Thread.usleep (10000);
-		}
-
-		// return & exit have the same effect
-		Thread.exit (get_ret_code ());
-		return 43;
-	}
+    public int x_times { get; private set; }
+
+    public MyThread (int times) {
+        this.x_times = times;
+    }
+
+    public int run () {
+        for (int i = 0; i < this.x_times; i++) {
+            stdout.printf ("ping! %d/%d\n", i + 1, this.x_times);
+            Thread.usleep (10000);
+        }
+
+        // return & exit have the same effect
+        Thread.exit (get_ret_code ());
+        return 43;
+    }
 }
 
 public static int main (string[] args) {
-	// Check whether threads are supported:
-	if (Thread.supported () == false) {
-		stderr.printf ("Threads are not supported!\n");
-		return -1;
-	}
-
-	try {
-		// Start a thread:
-		MyThread my_thread = new MyThread (10);
-		Thread<int> thread = new Thread<int>.try ("My fst. thread", my_thread.run);
-
-		// Wait until thread finishes:
-		int result = thread.join ();
-		// Output: `Thread stopped! Return value: 42`
-		stdout.printf ("Thread stopped! Return value: %d\n", result);
-	} catch (Error e) {
-		stdout.printf ("Error: %s\n", e.message);
-	}
-
-	return 0;
+    // Check whether threads are supported:
+    if (Thread.supported () == false) {
+        stderr.printf ("Threads are not supported!\n");
+        return -1;
+    }
+
+    try {
+        // Start a thread:
+        MyThread my_thread = new MyThread (10);
+        Thread<int> thread = new Thread<int>.try ("My fst. thread", my_thread.run);
+
+        // Wait until thread finishes:
+        int result = thread.join ();
+        // Output: `Thread stopped! Return value: 42`
+        stdout.printf ("Thread stopped! Return value: %d\n", result);
+    } catch (Error e) {
+        stdout.printf ("Error: %s\n", e.message);
+    }
+
+    return 0;
 }
diff --git a/test cases/vala/9 gir/foo.vala b/test cases/vala/9 gir/foo.vala
index 00c48121a..bb6da1066 100644
--- a/test cases/vala/9 gir/foo.vala	
+++ b/test cases/vala/9 gir/foo.vala	
@@ -1,7 +1,7 @@
 namespace Foo
 {
-	public int bar ()
-	{
-		return 0;
-	}
+    public int bar ()
+    {
+        return 0;
+    }
 }