diff --git a/docs/options.rst b/docs/options.rst
index b0c4d228..e68c4a0d 100644
--- a/docs/options.rst
+++ b/docs/options.rst
@@ -219,6 +219,7 @@ Options for debugging language server
 -  ``--debug_filepath DEBUG_FILEPATH``         File path for language server tests
 -  ``--debug_rootpath DEBUG_ROOTPATH``         Root path for language server tests
 -  ``--debug_parser``                          Test source code parser on specified file
+-  ``--debug_preproc``                         Test preprocessor on specified file
 -  ``--debug_hover``                           Test `textDocument/hover` request for specified file and position
 -  ``--debug_rename RENAME_STRING``            Test `textDocument/rename` request for specified file and position
 -  ``--debug_actions``                         Test `textDocument/codeAction` request for specified file and position
diff --git a/fortls/__init__.py b/fortls/__init__.py
index 4405fd3f..e7e6c1f8 100644
--- a/fortls/__init__.py
+++ b/fortls/__init__.py
@@ -3,7 +3,13 @@
 import sys
 from multiprocessing import freeze_support
 
-from .debug import DebugError, debug_lsp, debug_parser, is_debug_mode
+from .debug import (
+    DebugError,
+    debug_lsp,
+    debug_parser,
+    debug_preprocessor,
+    is_debug_mode,
+)
 from .interface import cli
 from .jsonrpc import JSONRPC2Connection, ReadWriter
 from .langserver import LangServer
@@ -20,6 +26,9 @@ def main():
         if args.debug_parser:
             debug_parser(args)
 
+        elif args.debug_preproc:
+            debug_preprocessor(args)
+
         elif is_debug_mode(args):
             debug_lsp(args, vars(args))
 
diff --git a/fortls/debug.py b/fortls/debug.py
index 59803806..4a3c8c97 100644
--- a/fortls/debug.py
+++ b/fortls/debug.py
@@ -1,14 +1,16 @@
 from __future__ import annotations
 
+import logging
 import os
 import pprint
+import sys
 
 import json5
 
 from .helper_functions import only_dirs, resolve_globs
 from .jsonrpc import JSONRPC2Connection, ReadWriter, path_from_uri
 from .langserver import LangServer
-from .parsers.internal.parser import FortranFile
+from .parsers.internal.parser import FortranFile, preprocess_file
 
 
 class DebugError(Exception):
@@ -415,54 +417,11 @@ def debug_parser(args):
         The arguments parsed from the `ArgumentParser`
     """
 
-    def locate_config(root: str) -> str | None:
-        default_conf_files = [args.config, ".fortlsrc", ".fortls.json5", ".fortls"]
-        present_conf_files = [
-            os.path.isfile(os.path.join(root, f)) for f in default_conf_files
-        ]
-        if not any(present_conf_files):
-            return None
-
-        # Load the first config file found
-        for f, present in zip(default_conf_files, present_conf_files):
-            if not present:
-                continue
-            config_path = os.path.join(root, f)
-            return config_path
-
-    def read_config(root: str | None):
-        pp_suffixes = None
-        pp_defs = {}
-        include_dirs = set()
-        if root is None:
-            return pp_suffixes, pp_defs, include_dirs
-
-        # Check for config files
-        config_path = locate_config(root)
-        print(f"  Config file = {config_path}")
-        if config_path is None or not os.path.isfile(config_path):
-            return pp_suffixes, pp_defs, include_dirs
-
-        try:
-            with open(config_path, encoding="utf-8") as fhandle:
-                config_dict = json5.load(fhandle)
-                pp_suffixes = config_dict.get("pp_suffixes", None)
-                pp_defs = config_dict.get("pp_defs", {})
-                for path in config_dict.get("include_dirs", set()):
-                    include_dirs.update(only_dirs(resolve_globs(path, root)))
-
-                if isinstance(pp_defs, list):
-                    pp_defs = {key: "" for key in pp_defs}
-        except ValueError as e:
-            print(f"Error {e} while parsing '{config_path}' settings file")
-
-        return pp_suffixes, pp_defs, include_dirs
-
     print("\nTesting parser")
     separator()
 
     ensure_file_accessible(args.debug_filepath)
-    pp_suffixes, pp_defs, include_dirs = read_config(args.debug_rootpath)
+    pp_suffixes, pp_defs, include_dirs = read_config(args.debug_rootpath, args.config)
 
     print(f'  File = "{args.debug_filepath}"')
     file_obj = FortranFile(args.debug_filepath, pp_suffixes)
@@ -482,6 +441,56 @@ def read_config(root: str | None):
     separator()
 
 
+def debug_preprocessor(args):
+    """Debug the preprocessor of the Language Server
+    Triggered by `--debug_preprocessor` option.
+
+    Parameters
+    ----------
+    args : Namespace
+        The arguments parsed from the `ArgumentParser`
+    """
+
+    def sep_lvl2(heading: str):
+        print("\n" + "=" * 75 + f"\n{heading}\n" + "=" * 75)
+
+    print("\nTesting preprocessor")
+    separator()
+
+    logging.basicConfig(level=logging.DEBUG, stream=sys.stdout, format="%(message)s")
+
+    file = args.debug_filepath
+    ensure_file_accessible(file)
+    with open(file, encoding="utf-8") as f:
+        lines = f.readlines()
+
+    root = args.debug_rootpath if args.debug_rootpath else os.path.dirname(file)
+    _, pp_defs, include_dirs = read_config(root, args.config)
+
+    sep_lvl2("Preprocessor Pass:")
+    output, skips, defines, defs = preprocess_file(
+        lines, file, pp_defs, include_dirs, debug=True
+    )
+
+    sep_lvl2("Preprocessor Skipped Lines:")
+    for line in skips:
+        print(f"  {line}")
+
+    sep_lvl2("Preprocessor Macros:")
+    for key, value in defs.items():
+        print(f"  {key} = {value}")
+
+    sep_lvl2("Preprocessor Defines (#define):")
+    for line in defines:
+        print(f"  {line}")
+
+    sep_lvl2("Preprocessor Final Output:")
+    for line in output:
+        print(rf"  {line.rstrip()}")
+
+    separator()
+
+
 def ensure_file_accessible(filepath: str):
     """Ensure the file exists and is accessible, raising an error if not."""
     if not os.path.isfile(filepath):
@@ -500,6 +509,51 @@ def check_request_params(args, loc_needed=True):
         print(f"  Char = {args.debug_char}\n")
 
 
+def locate_config(root: str, input_config: str) -> str | None:
+    default_conf_files = [input_config, ".fortlsrc", ".fortls.json5", ".fortls"]
+    present_conf_files = [
+        os.path.isfile(os.path.join(root, f)) for f in default_conf_files
+    ]
+    if not any(present_conf_files):
+        return None
+
+    # Load the first config file found
+    for f, present in zip(default_conf_files, present_conf_files):
+        if not present:
+            continue
+        config_path = os.path.join(root, f)
+        return config_path
+
+
+def read_config(root: str | None, input_config: str):
+    pp_suffixes = None
+    pp_defs = {}
+    include_dirs = set()
+    if root is None:
+        return pp_suffixes, pp_defs, include_dirs
+
+    # Check for config files
+    config_path = locate_config(root, input_config)
+    print(f"  Config file = {config_path}")
+    if config_path is None or not os.path.isfile(config_path):
+        return pp_suffixes, pp_defs, include_dirs
+
+    try:
+        with open(config_path, encoding="utf-8") as fhandle:
+            config_dict = json5.load(fhandle)
+            pp_suffixes = config_dict.get("pp_suffixes", None)
+            pp_defs = config_dict.get("pp_defs", {})
+            for path in config_dict.get("include_dirs", set()):
+                include_dirs.update(only_dirs(resolve_globs(path, root)))
+
+            if isinstance(pp_defs, list):
+                pp_defs = {key: "" for key in pp_defs}
+    except ValueError as e:
+        print(f"Error {e} while parsing '{config_path}' settings file")
+
+    return pp_suffixes, pp_defs, include_dirs
+
+
 def debug_generic(args, test_label, lsp_request, format_results, loc_needed=True):
     print(f'\nTesting "{test_label}" request:')
     check_request_params(args, loc_needed)
diff --git a/fortls/interface.py b/fortls/interface.py
index facc99a7..e16d0641 100644
--- a/fortls/interface.py
+++ b/fortls/interface.py
@@ -333,6 +333,11 @@ def hide_opt(help: str) -> str:
         action="store_true",
         help=hide_opt("Test source code parser on specified file"),
     )
+    group.add_argument(
+        "--debug_preproc",
+        action="store_true",
+        help=hide_opt("Test source code preprocessor parser on specified file"),
+    )
     group.add_argument(
         "--debug_hover",
         action="store_true",