diff --git a/navi/profiles/developer/system_prompt.txt b/navi/profiles/developer/system_prompt.txt
index c72fe45..85c26ba 100644
--- a/navi/profiles/developer/system_prompt.txt
+++ b/navi/profiles/developer/system_prompt.txt
@@ -44,6 +44,9 @@
 4. **Test** — run the code. Use `code_exec` or `terminal` to verify it works.
 5. **Report** — what was done, what was tested, any caveats.
 
+## Editing policy
+When editing existing files with `filesystem`, default to `edit` (exact text replacement — read the file first and copy `old` verbatim) or `edit_lines` (by line numbers). Both are deterministic and cheap. Reserve `smart_edit` (AI) for changes that genuinely cannot be expressed as exact text or line numbers — e.g. rename a symbol everywhere, add type hints to every function. Reaching for `smart_edit` on every edit is wasteful and error-prone: it reads the whole file and makes an extra LLM call with less context than you already have.
+
 ---
 
 ## Project knowledge
diff --git a/navi/profiles/navi_code/system_prompt.txt b/navi/profiles/navi_code/system_prompt.txt
index 0716667..7ca6a1a 100644
--- a/navi/profiles/navi_code/system_prompt.txt
+++ b/navi/profiles/navi_code/system_prompt.txt
@@ -44,6 +44,9 @@
 4. **Test** — run the code. Use `code_exec` or `terminal` to verify it works.
 5. **Report** — what was done, what was tested, any caveats.
 
+## Editing policy
+When editing existing files with `filesystem`, default to `edit` (exact text replacement — read the file first and copy `old` verbatim) or `edit_lines` (by line numbers). Both are deterministic and cheap. Reserve `smart_edit` (AI) for changes that genuinely cannot be expressed as exact text or line numbers — e.g. rename a symbol everywhere, add type hints to every function. Reaching for `smart_edit` on every edit is wasteful and error-prone: it reads the whole file and makes an extra LLM call with less context than you already have.
+
 
 --- 
 
diff --git a/navi/tools/filesystem.py b/navi/tools/filesystem.py
index 8502d8a..576d24f 100644
--- a/navi/tools/filesystem.py
+++ b/navi/tools/filesystem.py
@@ -279,13 +279,22 @@
 class FilesystemTool(Tool):
     name = "filesystem"
     description = (
-        "Operate on the local filesystem. "
-        "Decision tree — pick the cheapest option for your task:\n"
-        "1. Need to extract info from a file — use 'query' (pass 'question').\n"
-        "2. Small exact edit — use 'edit' with 'old' and 'new' text, or 'edit_lines' with line numbers.\n"
-        "3. Semantic edit (intent known, exact text unknown) — use 'smart_edit' (pass 'instruction').\n"
-        "4. Create or fully rewrite — use 'write' (pass 'content').\n"
-        "5. Everything else — standard actions: read, append, list, find, find_up, grep, diff, "
+        "Operate the local filesystem. "
+        "Editing policy — prefer the cheapest deterministic method; reach for "
+        "smart_edit LAST:\n"
+        "1. Edit by exact text — 'edit' with 'old' (must occur exactly once) and "
+        "'new'. Read the file first and copy old text verbatim. This is the "
+        "default for almost all edits.\n"
+        "2. Edit by line numbers — 'edit_lines' with an operations array, when "
+        "you know the exact lines (e.g. 'change line 15'). Deterministic, no AI "
+        "call.\n"
+        "3. smart_edit (AI) — ONLY as a fallback when the change genuinely cannot "
+        "be expressed as exact text or line numbers (e.g. 'rename a symbol "
+        "everywhere', 'add type hints to every function'). It costs an LLM call "
+        "and reads the whole file, so try edit/edit_lines first.\n"
+        "4. Create or fully rewrite a file — 'write' (pass 'content').\n"
+        "5. Extract info from a file — 'query' (pass 'question').\n"
+        "6. Everything else — read, append, list, find, find_up, grep, diff, "
         "info, copy, move, delete, exists, mkdir.\n"
         "Tip: call 'info' before reading an unknown file to check size."
     )
@@ -596,8 +605,10 @@
             return ToolResult(
                 success=False,
                 output=(
-                    f"Exact text occurs {count} times. Use a larger unique old text block "
-                    "or smart_edit for a semantic change."
+                    f"Exact text occurs {count} times. Prefer 'edit' with a larger "
+                    "unique 'old' block (include surrounding lines so it matches once) "
+                    "or 'edit_lines' with line numbers. Fall back to 'smart_edit' only if "
+                    "the change is genuinely semantic and cannot be expressed as exact text."
                 ),
                 error="old_not_unique",
             )
diff --git a/tests/unit/tools/test_filesystem.py b/tests/unit/tools/test_filesystem.py
index 0d558a0..e8dde50 100644
--- a/tests/unit/tools/test_filesystem.py
+++ b/tests/unit/tools/test_filesystem.py
@@ -171,6 +171,10 @@
         assert not result.success
         assert result.error == "old_not_unique"
         assert f.read_text() == "alpha beta beta"
+        # Hint steers back to edit/edit_lines first; smart_edit is a last resort.
+        assert "edit" in result.output
+        assert "edit_lines" in result.output
+        assert "smart_edit" in result.output
 
     async def test_copy_file(self, tool, tmp_path):
         src = tmp_path / "src.txt"