diff --git a/README.org b/README.org
index afafb553..c4f8cabd 100644
--- a/README.org
+++ b/README.org
@@ -152,6 +152,7 @@ Enable installation of packages from MELPA by adding an entry to package-archive
 - *Context-Aware Code Actions*: The menu exposes dedicated entries for changing code (`c`), implementing TODOs (`i`), asking questions (`q`), explaining code (`x`), sending free-form commands (`<SPC>`), and refreshing AI context (`@`). Each command automatically captures the surrounding function, region, or clipboard contents (via `C-u`) to keep prompts precise.
 - *Agile Development Workflows*: Use the refactoring navigator (`r`), the guided TDD cycle (`t`), and the pull/review diff helper (`v`) to keep AI-assisted work aligned with agile best practices. Prompt authoring is first-class through quick access to the prompt file (`p`), build/test helper (`b`), and AI-assisted shell/file execution (`!`). In prompt files, send the current block with `C-c C-c`.
 - *Productivity & Debugging Utilities*: Initialize project navigation assets (`.`), investigate exceptions (`e`), auto-fix Flycheck issues in scope (`f`), copy or open file paths formatted for prompts (`k`, `o`), generate MCP inspector commands (`m`), capture session notes straight into Org (`n`), dictate prompts with speech-to-text (`:`), and toggle desktop notifications (`N`) to get alerted when AI responses are ready in background sessions.
+- *Repo Guardrails Capture*: Derive a concise architecture guardrails file for the current repository with `C-c a A`. The command creates or updates `.ai.code.files/architecture/guardrails.org` so future AI coding sessions can reuse practical module boundaries, dependency rules, and validation expectations.
 - *Seamless Prompt Management*: Open the prompt file via `ai-code-open-prompt-file` (stored under `.ai.code.files/.ai.code.prompt.org` by default), send regions with `ai-code-prompt-send-block`, and reuse prompt snippets via `yasnippet` to keep conversations organized.
 - *Interactive Chat & Context Tools*: Dedicated buffers hold long-running chats, automatically enriched with file paths, diffs, and history from Magit or Git commands for richer AI responses.
 - *AI-Assisted Bash Commands*: From Dired, shell, eshell, or vterm, run `C-c a !` and type natural-language commands prefixed with `:` (e.g., `:count lines of python code recursively`); the tool generates the shell command for review and executes it in a compile buffer.
diff --git a/ai-code-discussion.el b/ai-code-discussion.el
index 566e8495..8b741fd1 100644
--- a/ai-code-discussion.el
+++ b/ai-code-discussion.el
@@ -679,6 +679,107 @@ This value is used by `ai-code-take-notes' when suggesting where to store notes.
   "Content of the most recent AI output"
   "Default request text for `ai-code-take-notes'.")
 
+(defconst ai-code-discussion--architecture-guardrails-file-name
+  "guardrails.org"
+  "File name for derived architecture guardrails.")
+
+(defconst ai-code-discussion--architecture-guardrails-directory-name
+  "architecture"
+  "Directory name for derived architecture guardrails.")
+
+(defconst ai-code-discussion--architecture-guardrails-template
+  (mapconcat #'identity
+             '("#+TITLE: Architecture Guardrails"
+               ""
+               "* Purpose"
+               ""
+               "* Important Modules / Areas"
+               ""
+               "* Dependency Rules"
+               ""
+               "* State and Ownership Rules"
+               ""
+               "* AI Change Rules"
+               ""
+               "* Required Validation"
+               ""
+               "* Notes and Uncertainties"
+               "")
+             "\n")
+  "Initial Org template for architecture guardrails.")
+
+(defun ai-code--architecture-guardrails-relative-path ()
+  "Return the repo-relative path for the architecture guardrails file."
+  (concat ai-code-files-dir-name "/"
+          ai-code-discussion--architecture-guardrails-directory-name "/"
+          ai-code-discussion--architecture-guardrails-file-name))
+
+(defun ai-code--architecture-guardrails-file-path ()
+  "Return the absolute path for the architecture guardrails file."
+  (expand-file-name ai-code-discussion--architecture-guardrails-file-name
+                    (expand-file-name
+                     ai-code-discussion--architecture-guardrails-directory-name
+                     (ai-code--ensure-files-directory))))
+
+(defun ai-code--ensure-architecture-guardrails-file ()
+  "Create the architecture guardrails file with a starter template if missing."
+  (let ((target-file (ai-code--architecture-guardrails-file-path)))
+    (unless (file-directory-p (file-name-directory target-file))
+      (make-directory (file-name-directory target-file) t))
+    (unless (file-exists-p target-file)
+      (with-temp-file target-file
+        (insert ai-code-discussion--architecture-guardrails-template)))
+    target-file))
+
+(defun ai-code--build-architecture-guardrails-prompt (git-root)
+  "Build the default prompt to derive architecture guardrails for GIT-ROOT."
+  (let ((relative-path (ai-code--architecture-guardrails-relative-path)))
+    (mapconcat
+     #'identity
+     (list "Derive a lightweight architecture guardrails document for this existing repository."
+            (format "Repository path: %s" git-root)
+            (format "Write or update @%s in Org-mode format." relative-path)
+            ""
+            "Infer practical module boundaries, dependency rules, state ownership rules, and validation expectations from the current code, tests, docs, and filenames."
+            "Do not invent an ideal architecture."
+            "Do not force DDD, Hexagonal Architecture, or Clean Architecture onto the repository."
+            "Prefer simple, practical rules over abstract architecture theory."
+            "Mark uncertain conclusions clearly."
+            "Focus on what helps future AI coding sessions avoid breaking boundaries or introducing messy dependencies."
+            "Do not suggest large refactors unless clearly separated as optional future ideas."
+            "Keep it concise, practical, and small enough to reuse in future AI prompts."
+            ""
+            "Use this Org structure:"
+            "#+TITLE: Architecture Guardrails"
+            ""
+            "* Purpose"
+            "* Important Modules / Areas"
+            "* Dependency Rules"
+            "* State and Ownership Rules"
+            "* AI Change Rules"
+            "* Required Validation"
+            "* Notes and Uncertainties"
+            ""
+            "If the file already exists, refine it instead of rewriting unrelated guidance.")
+     "\n")))
+
+;;;###autoload
+(defun ai-code-derive-architecture-guardrails ()
+  "Ask the current AI backend to derive repository architecture guardrails."
+  (interactive)
+  (let ((git-root (ai-code--git-root)))
+    (unless git-root
+      (user-error "Not in a git repository"))
+    (ai-code--ensure-architecture-guardrails-file)
+    (if-let ((final-prompt
+              (ai-code-read-string
+               "Prompt: "
+               (ai-code--build-architecture-guardrails-prompt git-root))))
+        (progn
+          (ai-code--insert-prompt final-prompt)
+          (message "Requested architecture guardrails for %s" git-root))
+      (message "Architecture guardrails request cancelled"))))
+
 (defun ai-code--get-note-candidates (default-note-file)
   "Get a list of candidate note files.
 DEFAULT-NOTE-FILE is included in the list.  Visible org buffers are prioritized."
diff --git a/ai-code.el b/ai-code.el
index e9955735..973d56a1 100644
--- a/ai-code.el
+++ b/ai-code.el
@@ -461,6 +461,7 @@ Shows the current backend label to the right."
   ("P" "AI session checkpoint" ai-code-session-checkpoint)
   ("e" "Debug exception (C-u: clipboard)" ai-code-investigate-exception)
   ("f" "Fix Flycheck errors in scope" ai-code-flycheck-fix-errors-in-scope)
+  ("A" "Derive Architecture Guardrails" ai-code-derive-architecture-guardrails)
   ("k" "Copy Cur File Name (C-u: full)" ai-code-copy-buffer-file-name-to-clipboard)
   ;; ("o" "Open recent file (C-u: insert)" ai-code-git-repo-recent-modified-files)
   ("p" "Open prompt history file" ai-code-open-prompt-file)
diff --git a/test/test_ai-code-discussion.el b/test/test_ai-code-discussion.el
index 565e6aa2..72973ead 100644
--- a/test/test_ai-code-discussion.el
+++ b/test/test_ai-code-discussion.el
@@ -447,6 +447,117 @@
       (ai-code-take-notes t)
       (should (equal captured-file "/tmp/project/.ai.code.files/test-notes.org")))))
 
+(ert-deftest ai-code-test-derive-architecture-guardrails-creates-template-and-prompt ()
+  "Test `ai-code-derive-architecture-guardrails' initializes the Org file and prompt."
+  (let* ((tmp-root (make-temp-file "ai-code-guardrails" t))
+         (target-file (expand-file-name ".ai.code.files/architecture/guardrails.org" tmp-root))
+         captured-initial-prompt
+         captured-final-prompt)
+    (unwind-protect
+        (cl-letf (((symbol-function 'ai-code--git-root)
+                   (lambda (&optional _dir)
+                     tmp-root))
+                  ((symbol-function 'ai-code-read-string)
+                   (lambda (prompt initial-input &optional _candidate-list)
+                     (should (equal prompt "Prompt: "))
+                     (setq captured-initial-prompt initial-input)
+                     initial-input))
+                  ((symbol-function 'ai-code--insert-prompt)
+                   (lambda (prompt)
+                     (setq captured-final-prompt prompt))))
+          (ai-code-derive-architecture-guardrails)
+          (should (file-exists-p target-file))
+          (with-temp-buffer
+            (insert-file-contents target-file)
+            (should (string-match-p (regexp-quote "#+TITLE: Architecture Guardrails")
+                                    (buffer-string)))
+            (should (string-match-p (regexp-quote "* Dependency Rules")
+                                    (buffer-string)))
+            (should (string-match-p (regexp-quote "* Required Validation")
+                                    (buffer-string))))
+          (should (string-match-p (regexp-quote "Derive a lightweight architecture guardrails document")
+                                  captured-initial-prompt))
+          (should (string-match-p (regexp-quote "current code, tests, docs, and filenames")
+                                  captured-initial-prompt))
+          (should (string-match-p (regexp-quote "Do not invent an ideal architecture")
+                                  captured-initial-prompt))
+          (should (string-match-p (regexp-quote "Keep it concise")
+                                  captured-initial-prompt))
+          (should (string-match-p (regexp-quote "@.ai.code.files/architecture/guardrails.org")
+                                  captured-initial-prompt))
+          (should (string-match-p (regexp-quote "Org-mode format")
+                                  captured-initial-prompt))
+          (should (equal captured-final-prompt captured-initial-prompt)))
+      (ignore-errors (delete-directory tmp-root t)))))
+
+(ert-deftest ai-code-test-derive-architecture-guardrails-preserves-existing-file ()
+  "Test `ai-code-derive-architecture-guardrails' does not overwrite an existing file."
+  (let* ((tmp-root (make-temp-file "ai-code-guardrails-existing" t))
+         (files-dir (expand-file-name ".ai.code.files/architecture" tmp-root))
+         (target-file (expand-file-name "guardrails.org" files-dir))
+         (existing-content "#+TITLE: Existing guardrails\n"))
+    (unwind-protect
+        (progn
+          (make-directory files-dir t)
+          (with-temp-file target-file
+            (insert existing-content))
+          (cl-letf (((symbol-function 'ai-code--git-root)
+                     (lambda (&optional _dir)
+                       tmp-root))
+                    ((symbol-function 'ai-code-read-string)
+                     (lambda (_prompt initial-input &optional _candidate-list)
+                       initial-input))
+                    ((symbol-function 'ai-code--insert-prompt)
+                     (lambda (_prompt))))
+            (ai-code-derive-architecture-guardrails))
+          (with-temp-buffer
+            (insert-file-contents target-file)
+            (should (equal (buffer-string) existing-content))))
+      (ignore-errors (delete-directory tmp-root t)))))
+
+(ert-deftest ai-code-test-derive-architecture-guardrails-errors-outside-git-repo ()
+  "Test `ai-code-derive-architecture-guardrails' requires a git repository."
+  (cl-letf (((symbol-function 'ai-code--git-root)
+             (lambda (&optional _dir)
+               nil)))
+    (should-error (ai-code-derive-architecture-guardrails)
+                  :type 'user-error)))
+
+(ert-deftest ai-code-test-derive-architecture-guardrails-reports-cancelled-request ()
+  "Test `ai-code-derive-architecture-guardrails' reports cancellation."
+  (let* ((tmp-root (make-temp-file "ai-code-guardrails-cancel" t))
+         captured-message
+         insert-called)
+    (unwind-protect
+        (cl-letf (((symbol-function 'ai-code--git-root)
+                   (lambda (&optional _dir)
+                     tmp-root))
+                  ((symbol-function 'ai-code-read-string)
+                   (lambda (&rest _args)
+                     nil))
+                  ((symbol-function 'ai-code--insert-prompt)
+                   (lambda (&rest _args)
+                     (setq insert-called t)))
+                  ((symbol-function 'message)
+                   (lambda (format-string &rest args)
+                     (setq captured-message
+                           (apply #'format format-string args)))))
+          (ai-code-derive-architecture-guardrails)
+          (should-not insert-called)
+          (should (equal captured-message
+                         "Architecture guardrails request cancelled")))
+      (ignore-errors (delete-directory tmp-root t)))))
+
+(ert-deftest ai-code-test-menu-source-includes-derive-architecture-guardrails-entry ()
+  "Test the menu source exposes the architecture guardrails command."
+  (let ((repo-root
+         (file-name-directory (locate-library "ai-code-discussion"))))
+    (with-temp-buffer
+      (insert-file-contents (expand-file-name "ai-code.el" repo-root))
+      (should (re-search-forward
+               "(\"A\" \"Derive Architecture Guardrails\" ai-code-derive-architecture-guardrails)"
+               nil t)))))
+
 (provide 'test_ai-code-discussion)
 
 ;;; test_ai-code-discussion.el ends here