diff --git a/lib/content/conformance.sh b/lib/content/conformance.sh
index e586f27e..3684cb6d 100755
--- a/lib/content/conformance.sh
+++ b/lib/content/conformance.sh
@@ -15,7 +15,7 @@ if [ ! -x "$SX_SERVER" ]; then
   fi
 fi
 
-SUITES=(block doc render api meta page page-full markdown text section compose tree-edit clone query toc transform normalize stats table data wire validate store snapshot crdt crdt-store sync md-import md-doc fed)
+SUITES=(block doc render api meta page page-full markdown text section compose tree-edit clone query toc transform normalize find-replace stats table data wire validate store snapshot crdt crdt-store sync md-import md-doc fed)
 
 OUT_JSON="lib/content/scoreboard.json"
 OUT_MD="lib/content/scoreboard.md"
@@ -52,6 +52,7 @@ run_suite() {
 (load "lib/content/toc.sx")
 (load "lib/content/transform.sx")
 (load "lib/content/normalize.sx")
+(load "lib/content/find-replace.sx")
 (load "lib/content/stats.sx")
 (load "lib/content/table.sx")
 (load "lib/content/data.sx")
diff --git a/lib/content/find-replace.sx b/lib/content/find-replace.sx
new file mode 100644
index 00000000..4c22e179
--- /dev/null
+++ b/lib/content/find-replace.sx
@@ -0,0 +1,31 @@
+;; content-on-sx — global find/replace across text-bearing blocks.
+;;
+;; Replaces every occurrence of `from` with `to` in the text field of text /
+;; heading / code / quote blocks, tree-wide (via the transform layer). For
+;; renaming a term throughout a document. Immutable; case-sensitive.
+;;
+;; Requires (loaded by harness): block.sx, transform.sx (content/map-blocks).
+
+(define
+  fr-in?
+  (fn
+    (x xs)
+    (cond
+      ((= (len xs) 0) false)
+      ((= (first xs) x) true)
+      (else (fr-in? x (rest xs))))))
+
+(define
+  fr-has-text?
+  (fn (b) (fr-in? (blk-type b) (list "text" "heading" "code" "quote"))))
+
+(define
+  content/find-replace
+  (fn
+    (doc from to)
+    (content/map-blocks
+      doc
+      fr-has-text?
+      (fn
+        (b)
+        (blk-set b "text" (replace (str (blk-get b "text")) from to))))))
diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index b1b199de..1dbfc1ac 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -17,6 +17,7 @@
     "toc": {"pass": 8, "fail": 0},
     "transform": {"pass": 12, "fail": 0},
     "normalize": {"pass": 11, "fail": 0},
+    "find-replace": {"pass": 10, "fail": 0},
     "stats": {"pass": 17, "fail": 0},
     "table": {"pass": 15, "fail": 0},
     "data": {"pass": 21, "fail": 0},
@@ -31,7 +32,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 605,
+  "total_pass": 615,
   "total_fail": 0,
-  "total": 605
+  "total": 615
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index 721ad016..a7211172 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -21,6 +21,7 @@ _Generated by `lib/content/conformance.sh`_
 | toc | 8 | 0 | 8 |
 | transform | 12 | 0 | 12 |
 | normalize | 11 | 0 | 11 |
+| find-replace | 10 | 0 | 10 |
 | stats | 17 | 0 | 17 |
 | table | 15 | 0 | 15 |
 | data | 21 | 0 | 21 |
@@ -34,4 +35,4 @@ _Generated by `lib/content/conformance.sh`_
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **605** | **0** | **605** |
+| **Total** | **615** | **0** | **615** |
diff --git a/lib/content/tests/find-replace.sx b/lib/content/tests/find-replace.sx
new file mode 100644
index 00000000..67e721d9
--- /dev/null
+++ b/lib/content/tests/find-replace.sx
@@ -0,0 +1,83 @@
+;; Extension — global find/replace across text-bearing blocks.
+
+(st-bootstrap-classes!)
+(content/bootstrap!)
+(content-bootstrap-section!)
+
+(define
+  d
+  (doc-append
+    (doc-append
+      (doc-append (doc-empty "d") (mk-heading "h" 1 "Foo title"))
+      (mk-text "p" "the Foo is here"))
+    (mk-section
+      "s"
+      (list (mk-text "n" "nested Foo") (mk-image "img" "/foo.png" "Foo alt")))))
+
+(define r (content/find-replace d "Foo" "Bar"))
+
+;; ── replaces in heading + text ──
+(content-test
+  "replace heading"
+  (str (blk-send (doc-deep-find r "h") "text"))
+  "Bar title")
+(content-test
+  "replace text"
+  (str (blk-send (doc-deep-find r "p") "text"))
+  "the Bar is here")
+(content-test
+  "replace nested text"
+  (str (blk-send (doc-deep-find r "n") "text"))
+  "nested Bar")
+
+;; ── does NOT touch image alt/src (not a text field) ──
+(content-test
+  "image alt untouched"
+  (str (blk-send (doc-deep-find r "img") "alt"))
+  "Foo alt")
+(content-test
+  "image src untouched"
+  (str (blk-send (doc-deep-find r "img") "src"))
+  "/foo.png")
+
+;; ── immutable ──
+(content-test
+  "original unchanged"
+  (str (blk-send (doc-deep-find d "p") "text"))
+  "the Foo is here")
+
+;; ── multiple occurrences in one block ──
+(content-test
+  "all occurrences"
+  (str
+    (blk-send
+      (doc-find
+        (content/find-replace
+          (doc-append (doc-empty "d") (mk-text "p" "a a a"))
+          "a"
+          "b")
+        "p")
+      "text"))
+  "b b b")
+
+;; ── code + quote text replaced ──
+(define
+  d2
+  (doc-append
+    (doc-append (doc-empty "d") (mk-code "c" "sx" "(old)"))
+    (mk-quote "q" "src" "old saying")))
+(define r2 (content/find-replace d2 "old" "new"))
+(content-test
+  "replace code"
+  (str (blk-send (doc-find r2 "c") "text"))
+  "(new)")
+(content-test
+  "replace quote"
+  (str (blk-send (doc-find r2 "q") "text"))
+  "new saying")
+
+;; ── no match → unchanged render ──
+(content-test
+  "no match"
+  (asHTML (content/find-replace d "zzz" "qqq"))
+  (asHTML d))
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index 34b06654..33238787 100644
--- a/plans/content-on-sx.md
+++ b/plans/content-on-sx.md
@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **605/605** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CRDT replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees + deep tree editing, doc stats, table block, HTML page wrapper + SEO page, doc composition + id-remap, portable data + wire serialization, block query + transforms, TOC rendering, normalization)
+`bash lib/content/conformance.sh` → **615/615** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CRDT replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees + deep tree editing, doc stats, table block, HTML page wrapper + SEO page, doc composition + id-remap, portable data + wire serialization, block query + transforms + find/replace, TOC rendering, normalization)
 
 ## Ground rules
 
@@ -98,11 +98,17 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [x] block transforms (`transform.sx`: content/map-blocks/map-type/set-field-on)
 - [x] TOC rendering (`toc.sx`: content/toc-markdown + toc-html from headings)
 - [x] document normalization (`normalize.sx`: content/normalize, drop empty blocks/sections)
+- [x] global find/replace (`find-replace.sx`: content/find-replace across text-bearing blocks)
 - [x] portable data serialization (`data.sx`: content/to-data + from-data, round-trips tree)
 - [x] wire serialization (`wire.sx`: content/to-wire + from-wire, SX-text on the wire)
 
 ## Progress log
 
+- 2026-06-07 — Extension: global find/replace (`find-replace.sx`).
+  `content/find-replace` replaces every occurrence of a substring in the text
+  field of text/heading/code/quote blocks tree-wide (via the transform layer) —
+  rename a term throughout a doc. Leaves non-text fields (image alt/src) alone;
+  immutable, case-sensitive. 10 tests; suite 615/615.
 - 2026-06-07 — Extension: document normalization (`normalize.sx`).
   `content/normalize` drops empty text blocks and empty sections tree-wide;
   sections are normalised first so one emptied by the pass is itself removed.