diff --git a/lib/content/conformance.sh b/lib/content/conformance.sh
index 2f233e49..44845292 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 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 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"
@@ -48,6 +48,7 @@ run_suite() {
 (load "lib/content/compose.sx")
 (load "lib/content/tree-edit.sx")
 (load "lib/content/clone.sx")
+(load "lib/content/query.sx")
 (load "lib/content/stats.sx")
 (load "lib/content/table.sx")
 (load "lib/content/data.sx")
diff --git a/lib/content/query.sx b/lib/content/query.sx
new file mode 100644
index 00000000..a312a45b
--- /dev/null
+++ b/lib/content/query.sx
@@ -0,0 +1,51 @@
+;; content-on-sx — block query + table of contents.
+;;
+;; Collect blocks across the whole tree (descending into sections) by predicate
+;; or type, and derive a table of contents from headings. Tree detection is
+;; inline (class + st-iv-get) so this needs no section.sx.
+;;
+;; Requires (loaded by harness): block.sx, doc.sx.
+
+(define
+  qry-section?
+  (fn (b) (and (st-instance? b) (= (get b :class) "CtSection"))))
+(define
+  qry-tree
+  (fn
+    (blocks)
+    (if
+      (= (len blocks) 0)
+      (list)
+      (let
+        ((b (first blocks)))
+        (append
+          (cons
+            b
+            (if
+              (qry-section? b)
+              (let
+                ((ch (st-iv-get b "children")))
+                (if (list? ch) (qry-tree ch) (list)))
+              (list)))
+          (qry-tree (rest blocks)))))))
+
+(define
+  content/select
+  (fn (doc pred) (filter pred (qry-tree (doc-blocks doc)))))
+
+(define
+  content/select-type
+  (fn (doc type) (content/select doc (fn (b) (= (blk-type b) type)))))
+
+(define
+  content/count-type
+  (fn (doc type) (len (content/select-type doc type))))
+
+(define
+  content/select-ids
+  (fn (doc pred) (map (fn (b) (blk-id b)) (content/select doc pred))))
+
+;; table of contents: {:id :level :text} for every heading, in document order.
+(define
+  content/headings
+  (fn (doc) (map (fn (b) {:id (blk-id b) :text (blk-get b "text") :level (blk-get b "level")}) (content/select-type doc "heading"))))
diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index b714d62e..f21aeccc 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -13,6 +13,7 @@
     "compose": {"pass": 17, "fail": 0},
     "tree-edit": {"pass": 17, "fail": 0},
     "clone": {"pass": 10, "fail": 0},
+    "query": {"pass": 13, "fail": 0},
     "stats": {"pass": 17, "fail": 0},
     "table": {"pass": 15, "fail": 0},
     "data": {"pass": 21, "fail": 0},
@@ -27,7 +28,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 561,
+  "total_pass": 574,
   "total_fail": 0,
-  "total": 561
+  "total": 574
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index 4499a6ac..1f2d0463 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -17,6 +17,7 @@ _Generated by `lib/content/conformance.sh`_
 | compose | 17 | 0 | 17 |
 | tree-edit | 17 | 0 | 17 |
 | clone | 10 | 0 | 10 |
+| query | 13 | 0 | 13 |
 | stats | 17 | 0 | 17 |
 | table | 15 | 0 | 15 |
 | data | 21 | 0 | 21 |
@@ -30,4 +31,4 @@ _Generated by `lib/content/conformance.sh`_
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **561** | **0** | **561** |
+| **Total** | **574** | **0** | **574** |
diff --git a/lib/content/tests/query.sx b/lib/content/tests/query.sx
new file mode 100644
index 00000000..873c82cc
--- /dev/null
+++ b/lib/content/tests/query.sx
@@ -0,0 +1,89 @@
+;; Extension — block query + table of contents.
+
+(st-bootstrap-classes!)
+(content/bootstrap!)
+(content-bootstrap-section!)
+
+(define
+  d
+  (doc-append
+    (doc-append
+      (doc-append
+        (doc-append (doc-empty "d") (mk-heading "h1" 1 "Intro"))
+        (mk-text "p1" "para"))
+      (mk-image "img" "/a.png" "alt"))
+    (mk-section
+      "s"
+      (list
+        (mk-heading "h2" 2 "Sub")
+        (mk-text "p2" "more")
+        (mk-image "img2" "/b.png" "b")))))
+
+;; ── select-type (tree-wide) ──
+(content-test
+  "select headings ids"
+  (map (fn (b) (blk-id b)) (content/select-type d "heading"))
+  (list "h1" "h2"))
+(content-test
+  "select images ids"
+  (map (fn (b) (blk-id b)) (content/select-type d "image"))
+  (list "img" "img2"))
+(content-test
+  "select text ids"
+  (map (fn (b) (blk-id b)) (content/select-type d "text"))
+  (list "p1" "p2"))
+(content-test
+  "select section ids"
+  (map (fn (b) (blk-id b)) (content/select-type d "section"))
+  (list "s"))
+
+;; ── count-type ──
+(content-test "count headings" (content/count-type d "heading") 2)
+(content-test "count images" (content/count-type d "image") 2)
+(content-test "count dividers" (content/count-type d "divider") 0)
+
+;; ── select with custom predicate ──
+(content-test
+  "select-ids custom"
+  (content/select-ids d (fn (b) (= (blk-type b) "image")))
+  (list "img" "img2"))
+(content-test
+  "select custom field"
+  (map
+    (fn (b) (blk-id b))
+    (content/select
+      d
+      (fn
+        (b)
+        (if
+          (= (blk-type b) "heading")
+          (= (blk-get b "level") 2)
+          false))))
+  (list "h2"))
+
+;; ── headings / TOC ──
+(content-test
+  "headings TOC"
+  (content/headings d)
+  (list {:id "h1" :text "Intro" :level 1} {:id "h2" :text "Sub" :level 2}))
+(content-test
+  "empty doc no headings"
+  (content/headings (doc-empty "e"))
+  (list))
+
+;; ── deeply nested ──
+(define
+  deep
+  (doc-append
+    (doc-empty "d")
+    (mk-section
+      "o"
+      (list (mk-section "i" (list (mk-heading "deep" 3 "Deep")))))))
+(content-test
+  "deep heading found"
+  (map (fn (b) (blk-id b)) (content/select-type deep "heading"))
+  (list "deep"))
+(content-test
+  "deep toc level"
+  (get (first (content/headings deep)) :level)
+  3)
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index 0ab3a5eb..048bffbe 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` → **561/561** (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)
+`bash lib/content/conformance.sh` → **574/574** (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 + TOC)
 
 ## Ground rules
 
@@ -94,11 +94,17 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [x] document composition (`compose.sx`: concat/prepend/concat-all/wrap-section)
 - [x] deep tree editing (`tree-edit.sx`: doc-deep-update/replace/delete/insert-into)
 - [x] id remapping / clone (`clone.sx`: content/remap-ids + prefix-ids, collision-free compose)
+- [x] block query + TOC (`query.sx`: content/select/select-type/count-type/headings)
 - [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: block query + TOC (`query.sx`). `content/select`
+  (predicate) / `content/select-type` / `content/count-type` / `content/select-ids`
+  collect blocks across the whole tree (sections recurse); `content/headings`
+  derives a table of contents (`{:id :level :text}` per heading, document order).
+  Inline tree detection (no section.sx dep). 13 tests; suite 574/574.
 - 2026-06-07 — Extension: id remapping / clone (`clone.sx`).
   `content/remap-ids` deep-rewrites every block id across the tree (sections
   recurse) via a function; `content/prefix-ids` prefixes them. Enables