diff --git a/lib/content/conformance.sh b/lib/content/conformance.sh
index 7158b62b..4c4ab5b5 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 stats table data 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 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"
@@ -49,6 +49,7 @@ run_suite() {
 (load "lib/content/stats.sx")
 (load "lib/content/table.sx")
 (load "lib/content/data.sx")
+(load "lib/content/wire.sx")
 (load "lib/content/page.sx")
 (load "lib/content/page-full.sx")
 (load "lib/content/markdown.sx")
diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index adee7c9d..6a90f654 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -14,6 +14,7 @@
     "stats": {"pass": 17, "fail": 0},
     "table": {"pass": 15, "fail": 0},
     "data": {"pass": 21, "fail": 0},
+    "wire": {"pass": 11, "fail": 0},
     "validate": {"pass": 23, "fail": 0},
     "store": {"pass": 29, "fail": 0},
     "snapshot": {"pass": 20, "fail": 0},
@@ -24,7 +25,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 523,
+  "total_pass": 534,
   "total_fail": 0,
-  "total": 523
+  "total": 534
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index f144b600..9497efba 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -18,6 +18,7 @@ _Generated by `lib/content/conformance.sh`_
 | stats | 17 | 0 | 17 |
 | table | 15 | 0 | 15 |
 | data | 21 | 0 | 21 |
+| wire | 11 | 0 | 11 |
 | validate | 23 | 0 | 23 |
 | store | 29 | 0 | 29 |
 | snapshot | 20 | 0 | 20 |
@@ -27,4 +28,4 @@ _Generated by `lib/content/conformance.sh`_
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **523** | **0** | **523** |
+| **Total** | **534** | **0** | **534** |
diff --git a/lib/content/tests/wire.sx b/lib/content/tests/wire.sx
new file mode 100644
index 00000000..afa289f0
--- /dev/null
+++ b/lib/content/tests/wire.sx
@@ -0,0 +1,63 @@
+;; Extension — on-the-wire serialization (to-wire / from-wire).
+
+(st-bootstrap-classes!)
+(content/bootstrap!)
+(content-bootstrap-text!)
+(content-bootstrap-section!)
+(content-bootstrap-table!)
+
+(define
+  d
+  (doc-with-meta
+    (doc-append
+      (doc-append (doc-empty "post") (mk-heading "h" 1 "Title"))
+      (mk-text "p" "Body text"))
+    {:title "T" :tags (list "x" "y")}))
+
+;; ── to-wire produces a string ──
+(content-test "to-wire is string" (string? (content/to-wire d)) true)
+
+;; ── parse(to-wire) == data form ──
+(content-test
+  "wire parses to data"
+  (parse (content/to-wire d))
+  (content/to-data d))
+
+;; ── round-trip preserves everything ──
+(define rt (content/wire-round-trip d))
+(content-test "rt id" (doc-id rt) "post")
+(content-test "rt title" (doc-title rt) "T")
+(content-test "rt tags" (doc-tags rt) (list "x" "y"))
+(content-test "rt ids" (doc-ids rt) (list "h" "p"))
+(content-test "rt render" (asHTML rt) (asHTML d))
+
+;; ── nested + table survive the wire ──
+(define
+  dn
+  (doc-append
+    (doc-append
+      (doc-empty "d")
+      (mk-section "s" (list (mk-text "a" "deep"))))
+    (mk-table "t" (list "A") (list (list "1")))))
+(content-test
+  "wire nested render"
+  (asHTML (content/wire-round-trip dn))
+  (asHTML dn))
+(content-test
+  "wire nested tree-ids"
+  (doc-tree-ids (content/wire-round-trip dn))
+  (doc-tree-ids dn))
+
+;; ── empty doc ──
+(content-test
+  "wire empty"
+  (doc-ids (content/from-wire (content/to-wire (doc-empty "e"))))
+  (list))
+
+;; ── from-wire of an externally-built wire string ──
+(content-test
+  "from-wire external"
+  (asHTML
+    (content/from-wire
+      "{:id \"x\" :blocks ({:id \"h\" :type \"heading\" :fields {:level 2 :text \"Hi\"}})}"))
+  "<h2>Hi</h2>")
diff --git a/lib/content/wire.sx b/lib/content/wire.sx
new file mode 100644
index 00000000..974b60b1
--- /dev/null
+++ b/lib/content/wire.sx
@@ -0,0 +1,14 @@
+;; content-on-sx — on-the-wire serialization.
+;;
+;; content/to-wire serialises a document to a transmittable SX-text string (via
+;; the data form + the SX serializer); content/from-wire parses it back into a
+;; live document. This is the format to persist a whole document or send it over
+;; HTTP / federation, distinct from the per-op persist log.
+;;
+;; Requires (loaded by harness): data.sx (content/to-data / content/from-data).
+
+(define content/to-wire (fn (doc) (serialize (content/to-data doc))))
+(define content/from-wire (fn (s) (content/from-data (parse s))))
+(define
+  content/wire-round-trip
+  (fn (doc) (content/from-wire (content/to-wire doc))))
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index 49326b10..b11f284b 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` → **523/523** (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, doc stats, table block, HTML page wrapper + SEO page, doc composition, portable data serialization)
+`bash lib/content/conformance.sh` → **534/534** (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, doc stats, table block, HTML page wrapper + SEO page, doc composition, portable data + wire serialization)
 
 ## Ground rules
 
@@ -93,9 +93,16 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [x] SEO page (`page-full.sx`: content/page-full, lang + meta description from excerpt)
 - [x] document composition (`compose.sx`: concat/prepend/concat-all/wrap-section)
 - [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: on-the-wire serialization (`wire.sx`).
+  `content/to-wire` serialises a document to a transmittable SX-text string (data
+  form + SX serializer); `content/from-wire` parses it back into a live document.
+  The whole-document format for persistence / HTTP / federation (distinct from
+  the per-op persist log); round-trips nested trees + tables; reads externally
+  authored wire strings. 11 tests; suite 534/534.
 - 2026-06-07 — Extension: portable data serialization (`data.sx`).
   `content/to-data` converts a document to plain SX data
   (`{:id :title :slug :tags :blocks [{:id :type :fields}]}`, sections recursing);