diff --git a/CLAUDE.md b/CLAUDE.md
index 068af96..850bd16 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -82,6 +82,7 @@ Blocks support fence options (e.g., ` ```nushell try, no-output `):
 - `try` / `t`: Wrap in try-catch
 - `new-instance` / `n`: Execute in separate Nushell instance
 - `separate-block` / `s`: Output results in separate code block instead of inline `# =>`
+- `run-once`: Execute code block once, then set to `no-run`
 
 ### Output Format Conventions
 
diff --git a/numd/commands.nu b/numd/commands.nu
index 883793d..b035146 100644
--- a/numd/commands.nu
+++ b/numd/commands.nu
@@ -256,7 +256,7 @@ export def decorate-original-code-blocks [
     | insert code {|i|
         $i.line
         | process-code-block-content ($i.row_type | extract-fence-options)
-        | generate-block-markers $i.block_index $i.row_type
+        | generate-block-markers $i.block_index ($i.row_type | str replace 'run-once' 'no-run')
     }
 }
 
@@ -648,7 +648,7 @@ export def generate-block-markers [
 }
 
 # Parse options from a code fence and return them as a list.
-@example "parse fence options with short forms" { '```nu no-run, t' | extract-fence-options } --result [no-run, try]
+@example "parse fence options with short forms" { '```nu no-run, t' | extract-fence-options } --result [no-run try]
 export def extract-fence-options []: string -> list<string> {
     str replace -r '```nu(shell)?\s*' ''
     | split row ','
diff --git a/tests/test_commands.nu b/tests/test_commands.nu
index a232bef..19ab290 100644
--- a/tests/test_commands.nu
+++ b/tests/test_commands.nu
@@ -82,6 +82,16 @@ def "classify-block-action returns print-as-it-is for no-run" [] {
     assert equal (classify-block-action "```nushell no-run") "print-as-it-is"
 }
 
+@test
+def "classify-block-action returns execute for run-once" [] {
+    assert equal (classify-block-action "```nushell run-once") "execute"
+}
+
+@test
+def "classify-block-action returns execute for run-once combined with try" [] {
+    assert equal (classify-block-action "```nushell run-once, try") "execute"
+}
+
 @test
 def "classify-block-action returns delete for output-numd" [] {
     assert equal (classify-block-action "```output-numd") "delete"
@@ -126,6 +136,22 @@ def "extract-fence-options expands short options" [] {
     assert ("no-output" in $result)
 }
 
+@test
+def "extract-fence-options parses run-once" [] {
+    let result = "```nu run-once" | extract-fence-options
+
+    assert equal $result ["run-once"]
+}
+
+@test
+def "extract-fence-options parses run-once combined with try" [] {
+    let result = "```nu run-once, try" | extract-fence-options
+
+    assert equal ($result | length) 2
+    assert ("run-once" in $result)
+    assert ("try" in $result)
+}
+
 @test
 def "extract-fence-options handles empty options" [] {
     let result = "```nushell" | extract-fence-options
@@ -375,6 +401,37 @@ def "generate-timestamp returns correct format" [] {
     assert ($result =~ '^\d{8}_\d{6}$')
 }
 
+# =============================================================================
+# Tests for decorate-original-code-blocks (run-once rewriting)
+# =============================================================================
+
+@test
+def "decorate-original-code-blocks rewrites run-once to no-run" [] {
+    let blocks = "```nu run-once\necho hello\n```" | parse-markdown-to-blocks
+    let result = decorate-original-code-blocks $blocks
+
+    assert ($result.0.code =~ '```nu no-run')
+    assert ($result.0.code !~ 'run-once')
+}
+
+@test
+def "decorate-original-code-blocks rewrites run-once preserving other options" [] {
+    let blocks = "```nu run-once, try\necho hello\n```" | parse-markdown-to-blocks
+    let result = decorate-original-code-blocks $blocks
+
+    assert ($result.0.code =~ '```nu no-run, try')
+    assert ($result.0.code !~ 'run-once')
+}
+
+@test
+def "decorate-original-code-blocks leaves plain blocks unchanged" [] {
+    let blocks = "```nu\necho hello\n```" | parse-markdown-to-blocks
+    let result = decorate-original-code-blocks $blocks
+
+    assert ($result.0.code =~ '```nu')
+    assert ($result.0.code !~ 'no-run')
+}
+
 # =============================================================================
 # Tests for strip-outputs
 # =============================================================================
diff --git a/z_examples/6_edge_cases/run_once.md b/z_examples/6_edge_cases/run_once.md
new file mode 100644
index 0000000..f2241f9
--- /dev/null
+++ b/z_examples/6_edge_cases/run_once.md
@@ -0,0 +1,13 @@
+# run-once fence option
+
+After numd run, the run-once block below should become no-run with output preserved.
+
+```nu run-once
+2 + 2
+```
+
+This block uses run-once combined with no-output.
+
+```nu run-once, no-output
+3 + 3
+```