diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index 1e79a1045..9a8006ef3 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -11,4 +11,5 @@
 | stevemullerworth | Steve Mullerworth | Met Office  | 2026-01-08 |
 | harry-shepherd  | Harry Shepherd   | Met Office  | 2026-01-08 |
 | EdHone          | Ed Hone          | Met Office  | 2026-01-09 |
+| mo-lucy-gordon  | Lucy Gordon      | Met Office  | 2026-01-14 |
 
diff --git a/infrastructure/fortitude.toml b/infrastructure/fortitude.toml
new file mode 100644
index 000000000..2019891b4
--- /dev/null
+++ b/infrastructure/fortitude.toml
@@ -0,0 +1,14 @@
+##############################################################################
+# (c) Crown copyright Met Office. All rights reserved.
+# The file LICENCE, distributed with this code, contains details of the terms
+# under which the code may be used.
+##############################################################################
+
+[check]
+
+file-extensions= ["f90", "F90", "X90", "x90"]          #check these file types
+
+
+select = ["C121"]
+
+output-format = "grouped"                #group results by file
diff --git a/rose-stem/app/check_fortitude_linter/file/fortitude.toml b/rose-stem/app/check_fortitude_linter/file/fortitude.toml
new file mode 100644
index 000000000..577dcd310
--- /dev/null
+++ b/rose-stem/app/check_fortitude_linter/file/fortitude.toml
@@ -0,0 +1,15 @@
+##############################################################################
+# (c) Crown copyright Met Office. All rights reserved.
+# The file LICENCE, distributed with this code, contains details of the terms
+# under which the code may be used.
+##############################################################################
+
+[check]
+
+file-extensions= ["f90", "F90", "X90",  "x90"]          #check these file types
+
+
+select = ["C121"]
+
+
+output-format = "grouped"                #group results by file
diff --git a/rose-stem/app/check_fortitude_linter/rose-app.conf b/rose-stem/app/check_fortitude_linter/rose-app.conf
new file mode 100644
index 000000000..e20cad3bb
--- /dev/null
+++ b/rose-stem/app/check_fortitude_linter/rose-app.conf
@@ -0,0 +1,2 @@
+[command]
+default=$CYLC_WORKFLOW_RUN_DIR/bin/fortitude_launcher.py -s $SOURCE_ROOT/lfric_core
diff --git a/rose-stem/bin/fortitude_launcher.py b/rose-stem/bin/fortitude_launcher.py
new file mode 100755
index 000000000..d39729af3
--- /dev/null
+++ b/rose-stem/bin/fortitude_launcher.py
@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+##############################################################################
+# (c) Crown copyright Met Office. All rights reserved.
+# The file LICENCE, distributed with this code, contains details of the terms
+# under which the code may be used.
+##############################################################################
+
+"""
+Launch fortitude on list of directories. Run on all and print outputs. Fail if
+any style changes required.
+"""
+
+import argparse
+import os
+import subprocess
+import sys
+
+
+def launch_fortitude(config_path, app_path):
+    """
+    Launch fortitude as a subprocess command and check the output
+    """
+
+    command = f"fortitude --config-file {config_path} check {app_path}"
+    result = subprocess.run(command.split(), capture_output=True, text=True)
+
+    print(result.stdout)
+    return result
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        description="Run fortitude on all applications. If "
+        "application/fortitude.toml exists use that file, otherwise "
+        "use one in rose-stem/app/check_fortitude_linter/file. "
+        "Print output, raise error if any changes required."
+    )
+    parser.add_argument(
+        "-s",
+        "--source",
+        help="The top level of lfric_core directory.",
+        required=True,
+    )
+    args = parser.parse_args()
+
+    failed_apps = {}
+
+    candidates = [
+        "infrastructure",
+        "mesh_tools",
+        "components/coupling",
+        "components/driver",
+        "components/science",
+        "components/inventory",
+        "components/lfric-xios",
+        "applications/skeleton",
+        "applications/simple_diffusion",
+        "applications/io_demo",
+    ]
+    for app in candidates:
+        print(f"Running on {app}\n")
+        app_path = os.path.join(args.source, app)
+        config_path = os.path.join(app_path, "fortitude.toml")
+        if not os.path.exists(os.path.join(config_path)):
+            print("Using universal config (toml) file."
+                  " (Some apps use their own config file.)")
+            config_path = os.path.join(
+                args.source,
+                "rose-stem",
+                "app",
+                "check_fortitude_linter",
+                "file",
+                "fortitude.toml",
+            )
+
+        result = launch_fortitude(config_path, app_path)
+        if result.returncode:
+            # prints the app run on if there are errors of any kind
+            print(f"Checking: {app} \n", file=sys.stderr)
+            if not result.stderr:
+                # prints if no other/config errors are found
+                print("Found lint errors:", file=sys.stderr)
+                # prints the lint errors
+                print(result.stdout, file=sys.stderr)
+            if result.stderr:
+                # prints if there are other/config errors
+                print("Found non-lint errors: \n", file=sys.stderr)
+                # prints the other/config error
+                print(result.stderr, "\n\n\n", file=sys.stderr)
+            failed_apps[app] = result.stderr
+
+    if failed_apps:
+        error_message = ""
+        print("\n\n\nSummary: Fortitude found errors in"
+              " the following repositories:\n", file=sys.stderr)
+        for failed in failed_apps:
+            error_message += f"{failed}\n"
+        sys.exit(error_message)
diff --git a/rose-stem/site/meto/groups.cylc b/rose-stem/site/meto/groups.cylc
index 2452ddd76..62646ad80 100644
--- a/rose-stem/site/meto/groups.cylc
+++ b/rose-stem/site/meto/groups.cylc
@@ -9,6 +9,7 @@
     "scripts": [
         "config_dump_checker",
         "style_checker",
+        "fortitude_linter",
         "site_validator",
         "validate_rose_meta",
         "rose-stem_lint_checker",
diff --git a/rose-stem/templates/graph/populate_graph_scripts.cylc b/rose-stem/templates/graph/populate_graph_scripts.cylc
index 25e0eeda1..2aa328729 100644
--- a/rose-stem/templates/graph/populate_graph_scripts.cylc
+++ b/rose-stem/templates/graph/populate_graph_scripts.cylc
@@ -51,6 +51,7 @@
     {# * config_dump_checker #}
     {# * style_checker #}
     {# * site_validator #}
+    {# * fortitude_linter #}
     {# * rose-stem_lint_checker #}
     {# * validate_rose_meta #}
     {# * global_variables_checker #}
diff --git a/rose-stem/templates/runtime/generate_runtime_scripts.cylc b/rose-stem/templates/runtime/generate_runtime_scripts.cylc
index 02faaf7b2..3c501f06f 100644
--- a/rose-stem/templates/runtime/generate_runtime_scripts.cylc
+++ b/rose-stem/templates/runtime/generate_runtime_scripts.cylc
@@ -36,6 +36,11 @@
         inherit={{inherit.str|upper}}
         script="rose task-run --app-key=check_style"
 
+{% elif "fortitude_linter" in task %}
+
+        inherit={{inherit.str|upper}}
+        script="rose task-run --app-key=check_fortitude_linter"
+
 {% elif "extract_checker" in task %}
 
         inherit={{inherit.str|upper}}