diff --git a/hosts/javascript/platform.py b/hosts/javascript/platform.py
index 8a3bb406..dc8f1e63 100644
--- a/hosts/javascript/platform.py
+++ b/hosts/javascript/platform.py
@@ -1702,6 +1702,67 @@ PRIMITIVES_JS_MODULES: dict[str, str] = {
     src.data.forEach(function(v, k) { dst.data.set(k, v); });
     return null;
   };
+''',
+    "stdlib.regexp": '''
+  // stdlib.regexp — native JS RegExp wrappers
+  function SxRegexp(source, flags) {
+    this._regexp = true;
+    this.source = source;
+    this.flags = flags || "";
+  }
+  function sxRxCompile(rx) {
+    if (!rx._compiled) {
+      var jsFlags = "";
+      if (rx.flags.indexOf("i") >= 0) jsFlags += "i";
+      if (rx.flags.indexOf("m") >= 0) jsFlags += "m";
+      if (rx.flags.indexOf("s") >= 0) jsFlags += "s";
+      rx._compiled = new RegExp(rx.source, jsFlags);
+    }
+    return rx._compiled;
+  }
+  function sxRxMatchDict(m, input) {
+    if (!m) return NIL;
+    var groups = [];
+    for (var i = 1; i < m.length; i++) groups.push(m[i] !== undefined ? m[i] : "");
+    return {"match": m[0], "start": m.index, "end": m.index + m[0].length,
+            "input": input, "groups": groups};
+  }
+  PRIMITIVES["make-regexp"] = function(src, flags) {
+    return new SxRegexp(src, flags || "");
+  };
+  PRIMITIVES["regexp?"] = function(v) { return v instanceof SxRegexp; };
+  PRIMITIVES["regexp-source"] = function(rx) { return rx.source; };
+  PRIMITIVES["regexp-flags"] = function(rx) { return rx.flags; };
+  PRIMITIVES["regexp-match"] = function(rx, s) {
+    var re = new RegExp(sxRxCompile(rx).source,
+      sxRxCompile(rx).flags.replace("g",""));
+    var m = s.match(re);
+    return sxRxMatchDict(m, s);
+  };
+  PRIMITIVES["regexp-match-all"] = function(rx, s) {
+    var compiled = sxRxCompile(rx);
+    var re = new RegExp(compiled.source, "g" + compiled.flags.replace("g",""));
+    var results = [], m;
+    while ((m = re.exec(s)) !== null) {
+      results.push(sxRxMatchDict(m, s));
+      if (m[0].length === 0) re.lastIndex++;
+    }
+    return results;
+  };
+  PRIMITIVES["regexp-replace"] = function(rx, s, replacement) {
+    var compiled = sxRxCompile(rx);
+    var re = new RegExp(compiled.source, compiled.flags.replace("g",""));
+    return s.replace(re, replacement);
+  };
+  PRIMITIVES["regexp-replace-all"] = function(rx, s, replacement) {
+    var compiled = sxRxCompile(rx);
+    var re = new RegExp(compiled.source, "g" + compiled.flags.replace("g",""));
+    return s.replace(re, replacement);
+  };
+  PRIMITIVES["regexp-split"] = function(rx, s) {
+    var re = sxRxCompile(rx);
+    return s.split(re);
+  };
 ''',
     "stdlib.sets": '''
   // stdlib.sets — structural sets keyed by write-to-string serialization
@@ -1802,6 +1863,7 @@ PLATFORM_JS_PRE = '''
     if (x._string_buffer) return "string-buffer";
     if (x._hash_table) return "hash-table";
     if (x._sxset) return "set";
+    if (x._regexp) return "regexp";
     if (x._rational) return "rational";
     if (typeof Node !== "undefined" && x instanceof Node) return "dom-node";
     if (Array.isArray(x)) return "list";
diff --git a/hosts/ocaml/lib/sx_primitives.ml b/hosts/ocaml/lib/sx_primitives.ml
index b7d8dfea..b4fced92 100644
--- a/hosts/ocaml/lib/sx_primitives.ml
+++ b/hosts/ocaml/lib/sx_primitives.ml
@@ -2224,6 +2224,127 @@ let () =
       String flags
     | _ -> raise (Eval_error "regex-flags: (regex)"));
 
+  (* make-regexp / regexp? / regexp-match / regexp-match-all / regexp-replace / regexp-replace-all / regexp-split *)
+  let parse_re_flags flags =
+    let opts = ref [] in
+    String.iter (function
+      | 'i' -> opts := `CASELESS :: !opts
+      | 'm' -> opts := `MULTILINE :: !opts
+      | 's' -> opts := `DOTALL :: !opts
+      | _ -> ()) flags;
+    !opts
+  in
+  let make_regexp_value source flags =
+    let opts = parse_re_flags flags in
+    try
+      let compiled = Re.compile (Re.Pcre.re ~flags:opts source) in
+      SxRegexp (source, flags, compiled)
+    with _ -> raise (Eval_error ("make-regexp: invalid pattern: " ^ source))
+  in
+  let match_dict g input =
+    let d = Hashtbl.create 4 in
+    Hashtbl.replace d "match" (String (Re.Group.get g 0));
+    Hashtbl.replace d "start" (Integer (Re.Group.start g 0));
+    Hashtbl.replace d "end" (Integer (Re.Group.stop g 0));
+    Hashtbl.replace d "input" (String input);
+    let count = Re.Group.nb_groups g in
+    let groups = ref [] in
+    for i = count - 1 downto 1 do
+      let s = try Re.Group.get g i with Not_found -> "" in
+      groups := String s :: !groups
+    done;
+    Hashtbl.replace d "groups" (List !groups);
+    Dict d
+  in
+  register "make-regexp" (fun args ->
+    match args with
+    | [String src] -> make_regexp_value src ""
+    | [String src; String flags] -> make_regexp_value src flags
+    | _ -> raise (Eval_error "make-regexp: (pattern [flags])"));
+  register "regexp?" (fun args ->
+    match args with
+    | [SxRegexp _] -> Bool true
+    | [_] -> Bool false
+    | _ -> raise (Eval_error "regexp?: 1 arg"));
+  register "regexp-source" (fun args ->
+    match args with
+    | [SxRegexp (src, _, _)] -> String src
+    | _ -> raise (Eval_error "regexp-source: expected regexp"));
+  register "regexp-flags" (fun args ->
+    match args with
+    | [SxRegexp (_, flags, _)] -> String flags
+    | _ -> raise (Eval_error "regexp-flags: expected regexp"));
+  register "regexp-match" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s] ->
+      (match Re.exec_opt re s with
+       | None -> Nil
+       | Some g -> match_dict g s)
+    | _ -> raise (Eval_error "regexp-match: (regexp string)"));
+  register "regexp-match-all" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s] ->
+      List (List.map (fun g -> match_dict g s) (Re.all re s))
+    | _ -> raise (Eval_error "regexp-match-all: (regexp string)"));
+  register "regexp-replace" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s; String replacement] ->
+      (match Re.exec_opt re s with
+       | None -> String s
+       | Some g ->
+         let buf = Buffer.create (String.length s) in
+         let i = ref 0 in
+         let n = String.length replacement in
+         let expand () =
+           while !i < n do
+             let c = replacement.[!i] in
+             if c = '$' && !i + 1 < n then
+               (match replacement.[!i + 1] with
+                | '&' -> Buffer.add_string buf (Re.Group.get g 0); i := !i + 2
+                | '$' -> Buffer.add_char buf '$'; i := !i + 2
+                | c when c >= '0' && c <= '9' ->
+                  let idx = Char.code c - Char.code '0' in
+                  (try Buffer.add_string buf (Re.Group.get g idx) with Not_found -> ());
+                  i := !i + 2
+                | _ -> Buffer.add_char buf c; incr i)
+             else (Buffer.add_char buf c; incr i)
+           done
+         in
+         Buffer.add_string buf (String.sub s 0 (Re.Group.start g 0));
+         expand ();
+         Buffer.add_string buf (String.sub s (Re.Group.stop g 0)
+           (String.length s - Re.Group.stop g 0));
+         String (Buffer.contents buf))
+    | _ -> raise (Eval_error "regexp-replace: (regexp string replacement)"));
+  register "regexp-replace-all" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s; String replacement] ->
+      let expand g =
+        let buf = Buffer.create (String.length replacement) in
+        let i = ref 0 in
+        let n = String.length replacement in
+        while !i < n do
+          let c = replacement.[!i] in
+          if c = '$' && !i + 1 < n then
+            (match replacement.[!i + 1] with
+             | '&' -> Buffer.add_string buf (Re.Group.get g 0); i := !i + 2
+             | '$' -> Buffer.add_char buf '$'; i := !i + 2
+             | c when c >= '0' && c <= '9' ->
+               let idx = Char.code c - Char.code '0' in
+               (try Buffer.add_string buf (Re.Group.get g idx) with Not_found -> ());
+               i := !i + 2
+             | _ -> Buffer.add_char buf c; incr i)
+          else (Buffer.add_char buf c; incr i)
+        done;
+        Buffer.contents buf
+      in
+      String (Re.replace re ~f:expand s)
+    | _ -> raise (Eval_error "regexp-replace-all: (regexp string replacement)"));
+  register "regexp-split" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s] ->
+      List (List.map (fun x -> String x) (Re.split re s))
+    | _ -> raise (Eval_error "regexp-split: (regexp string)"));
   (* Bitwise operations *)
   register "bitwise-and" (fun args ->
     match args with
diff --git a/hosts/ocaml/lib/sx_types.ml b/hosts/ocaml/lib/sx_types.ml
index 5f4f3ccd..cb1360b3 100644
--- a/hosts/ocaml/lib/sx_types.ml
+++ b/hosts/ocaml/lib/sx_types.ml
@@ -80,6 +80,7 @@ and value =
   | Port of sx_port  (** String port — input (string cursor) or output (buffer). *)
   | Rational of int * int  (** Exact rational: numerator, denominator (reduced, denom>0). *)
   | SxSet of (string, value) Hashtbl.t  (** Mutable set keyed by inspect(value). *)
+  | SxRegexp of string * string * Re.re  (** Regexp: source, flags, compiled. *)
 
 (** String input port: source string + mutable cursor position. *)
 and sx_port_kind =
@@ -516,6 +517,7 @@ let type_of = function
   | Port { sp_kind = PortOutput _; _ } -> "output-port"
   | Rational _  -> "rational"
   | SxSet _     -> "set"
+  | SxRegexp _  -> "regexp"
 
 let is_nil = function Nil -> true | _ -> false
 let is_lambda = function Lambda _ -> true | _ -> false
@@ -879,3 +881,4 @@ let rec inspect = function
     Printf.sprintf "<output-port:len=%d%s>" (Buffer.length buf) (if sp_closed then ":closed" else "")
   | Rational (n, d) -> Printf.sprintf "%d/%d" n d
   | SxSet ht -> Printf.sprintf "<set:%d>" (Hashtbl.length ht)
+  | SxRegexp (src, flags, _) -> Printf.sprintf "#/%s/%s" src flags
diff --git a/shared/static/scripts/sx-browser.js b/shared/static/scripts/sx-browser.js
index 40929353..eb83c190 100644
--- a/shared/static/scripts/sx-browser.js
+++ b/shared/static/scripts/sx-browser.js
@@ -41,7 +41,7 @@
   // =========================================================================
 
   var NIL = Object.freeze({ _nil: true, toString: function() { return "nil"; } });
-  var SX_VERSION = "2026-05-01T18:42:40Z";
+  var SX_VERSION = "2026-05-01T18:54:28Z";
 
   function isNil(x) { return x === NIL || x === null || x === undefined; }
   function isSxTruthy(x) { return x !== false && !isNil(x); }
@@ -185,6 +185,7 @@
     if (x._string_buffer) return "string-buffer";
     if (x._hash_table) return "hash-table";
     if (x._sxset) return "set";
+    if (x._regexp) return "regexp";
     if (x._rational) return "rational";
     if (typeof Node !== "undefined" && x instanceof Node) return "dom-node";
     if (Array.isArray(x)) return "list";
@@ -1097,6 +1098,67 @@
   };
 
 
+  // stdlib.regexp — native JS RegExp wrappers
+  function SxRegexp(source, flags) {
+    this._regexp = true;
+    this.source = source;
+    this.flags = flags || "";
+  }
+  function sxRxCompile(rx) {
+    if (!rx._compiled) {
+      var jsFlags = "";
+      if (rx.flags.indexOf("i") >= 0) jsFlags += "i";
+      if (rx.flags.indexOf("m") >= 0) jsFlags += "m";
+      if (rx.flags.indexOf("s") >= 0) jsFlags += "s";
+      rx._compiled = new RegExp(rx.source, jsFlags);
+    }
+    return rx._compiled;
+  }
+  function sxRxMatchDict(m, input) {
+    if (!m) return NIL;
+    var groups = [];
+    for (var i = 1; i < m.length; i++) groups.push(m[i] !== undefined ? m[i] : "");
+    return {"match": m[0], "start": m.index, "end": m.index + m[0].length,
+            "input": input, "groups": groups};
+  }
+  PRIMITIVES["make-regexp"] = function(src, flags) {
+    return new SxRegexp(src, flags || "");
+  };
+  PRIMITIVES["regexp?"] = function(v) { return v instanceof SxRegexp; };
+  PRIMITIVES["regexp-source"] = function(rx) { return rx.source; };
+  PRIMITIVES["regexp-flags"] = function(rx) { return rx.flags; };
+  PRIMITIVES["regexp-match"] = function(rx, s) {
+    var re = new RegExp(sxRxCompile(rx).source,
+      sxRxCompile(rx).flags.replace("g",""));
+    var m = s.match(re);
+    return sxRxMatchDict(m, s);
+  };
+  PRIMITIVES["regexp-match-all"] = function(rx, s) {
+    var compiled = sxRxCompile(rx);
+    var re = new RegExp(compiled.source, "g" + compiled.flags.replace("g",""));
+    var results = [], m;
+    while ((m = re.exec(s)) !== null) {
+      results.push(sxRxMatchDict(m, s));
+      if (m[0].length === 0) re.lastIndex++;
+    }
+    return results;
+  };
+  PRIMITIVES["regexp-replace"] = function(rx, s, replacement) {
+    var compiled = sxRxCompile(rx);
+    var re = new RegExp(compiled.source, compiled.flags.replace("g",""));
+    return s.replace(re, replacement);
+  };
+  PRIMITIVES["regexp-replace-all"] = function(rx, s, replacement) {
+    var compiled = sxRxCompile(rx);
+    var re = new RegExp(compiled.source, "g" + compiled.flags.replace("g",""));
+    return s.replace(re, replacement);
+  };
+  PRIMITIVES["regexp-split"] = function(rx, s) {
+    var re = sxRxCompile(rx);
+    return s.split(re);
+  };
+
+
   // stdlib.sets — structural sets keyed by write-to-string serialization
   function SxSet() { this.data = new Map(); this._sxset = true; }
   SxSet.prototype._type = "set";
diff --git a/spec/primitives.sx b/spec/primitives.sx
index 698396b6..59306a18 100644
--- a/spec/primitives.sx
+++ b/spec/primitives.sx
@@ -1196,3 +1196,59 @@
   :params (s fn)
   :returns "set"
   :doc "New set of results of (fn val) for each element in s.")
+
+(define-module :stdlib.regexp)
+
+(define-primitive
+  "make-regexp"
+  :params ((pattern :as string) &rest (flags :as string))
+  :returns "regexp"
+  :doc "Compile regexp from pattern string and optional flags string (\"i\" case-insensitive, \"m\" multiline, \"s\" dotall).")
+
+(define-primitive
+  "regexp?"
+  :params (v)
+  :returns "boolean"
+  :doc "True if v is a compiled regexp.")
+
+(define-primitive
+  "regexp-source"
+  :params ((re :as regexp))
+  :returns "string"
+  :doc "Pattern string of a regexp.")
+
+(define-primitive
+  "regexp-flags"
+  :params ((re :as regexp))
+  :returns "string"
+  :doc "Flags string of a regexp.")
+
+(define-primitive
+  "regexp-match"
+  :params ((re :as regexp) (str :as string))
+  :returns "any"
+  :doc "First match of re in str. Returns {:match \"...\" :start N :end N :groups (...)} or nil.")
+
+(define-primitive
+  "regexp-match-all"
+  :params ((re :as regexp) (str :as string))
+  :returns "list"
+  :doc "All non-overlapping matches of re in str as a list of match dicts.")
+
+(define-primitive
+  "regexp-replace"
+  :params ((re :as regexp) (str :as string) (replacement :as string))
+  :returns "string"
+  :doc "Replace first match of re in str with replacement. $& = whole match, $1..$9 = groups.")
+
+(define-primitive
+  "regexp-replace-all"
+  :params ((re :as regexp) (str :as string) (replacement :as string))
+  :returns "string"
+  :doc "Replace all matches of re in str with replacement.")
+
+(define-primitive
+  "regexp-split"
+  :params ((re :as regexp) (str :as string))
+  :returns "list"
+  :doc "Split str on every match of re; returns list of strings.")
diff --git a/spec/tests/test-regexp.sx b/spec/tests/test-regexp.sx
new file mode 100644
index 00000000..f883a47e
--- /dev/null
+++ b/spec/tests/test-regexp.sx
@@ -0,0 +1,191 @@
+;; ==========================================================================
+;; test-regexp.sx — Tests for regexp primitives
+;; ==========================================================================
+
+;; --------------------------------------------------------------------------
+;; make-regexp / regexp?
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:create"
+  (deftest "make-regexp returns regexp" (assert (regexp? (make-regexp "abc"))))
+  (deftest
+    "make-regexp with flags"
+    (assert (regexp? (make-regexp "[a-z]+" "i"))))
+  (deftest "regexp? true for regexp" (assert (regexp? (make-regexp "x"))))
+  (deftest "regexp? false for string" (assert (not (regexp? "abc"))))
+  (deftest "regexp? false for nil" (assert (not (regexp? nil))))
+  (deftest
+    "regexp-source"
+    (assert= (regexp-source (make-regexp "hello")) "hello"))
+  (deftest
+    "regexp-flags"
+    (assert= (regexp-flags (make-regexp "x" "im")) "im"))
+  (deftest
+    "regexp-flags empty string"
+    (assert= (regexp-flags (make-regexp "x")) "")))
+
+;; --------------------------------------------------------------------------
+;; regexp-match — basic
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:match"
+  (deftest
+    "match returns dict"
+    (let
+      ((m (regexp-match (make-regexp "hel+o") "hello world")))
+      (assert (dict? m))))
+  (deftest
+    "match :match key"
+    (let
+      ((m (regexp-match (make-regexp "hel+o") "say hello")))
+      (assert= (get m "match") "hello")))
+  (deftest
+    "match :start key"
+    (let
+      ((m (regexp-match (make-regexp "lo") "hello")))
+      (assert= (get m "start") 3)))
+  (deftest
+    "match :end key"
+    (let
+      ((m (regexp-match (make-regexp "lo") "hello")))
+      (assert= (get m "end") 5)))
+  (deftest
+    "no match returns nil"
+    (assert-nil (regexp-match (make-regexp "xyz") "hello")))
+  (deftest
+    "match at start"
+    (let
+      ((m (regexp-match (make-regexp "^hel") "hello")))
+      (assert= (get m "start") 0)))
+  (deftest
+    "match digit pattern"
+    (let
+      ((m (regexp-match (make-regexp "[0-9]+") "abc 123 def")))
+      (assert= (get m "match") "123"))))
+
+;; --------------------------------------------------------------------------
+;; regexp-match — groups
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:groups"
+  (deftest
+    "no capture groups → empty list"
+    (let
+      ((m (regexp-match (make-regexp "hello") "hello world")))
+      (assert= (length (get m "groups")) 0)))
+  (deftest
+    "one capture group"
+    (let
+      ((m (regexp-match (make-regexp "([0-9]+)") "price: 42")))
+      (assert= (first (get m "groups")) "42")))
+  (deftest
+    "two capture groups"
+    (let
+      ((m (regexp-match (make-regexp "([a-z]+)=([0-9]+)") "x=10")))
+      (let
+        ((gs (get m "groups")))
+        (assert
+          (and (= (first gs) "x") (= (first (rest gs)) "10")))))))
+
+;; --------------------------------------------------------------------------
+;; regexp-match-all
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:match-all"
+  (deftest
+    "match-all returns list"
+    (let
+      ((ms (regexp-match-all (make-regexp "[0-9]+") "1 and 2 and 3")))
+      (assert (list? ms))))
+  (deftest
+    "match-all count"
+    (assert=
+      (length (regexp-match-all (make-regexp "[0-9]+") "1 and 2 and 3"))
+      3))
+  (deftest
+    "match-all first match"
+    (let
+      ((ms (regexp-match-all (make-regexp "[0-9]+") "10 20 30")))
+      (assert= (get (first ms) "match") "10")))
+  (deftest
+    "match-all empty when no match"
+    (assert=
+      (length (regexp-match-all (make-regexp "xyz") "hello"))
+      0)))
+
+;; --------------------------------------------------------------------------
+;; regexp-replace / regexp-replace-all
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:replace"
+  (deftest
+    "replace first match"
+    (assert= (regexp-replace (make-regexp "o+") "foobar boo" "0") "f0bar boo"))
+  (deftest
+    "replace no match returns original"
+    (assert= (regexp-replace (make-regexp "xyz") "hello" "X") "hello"))
+  (deftest
+    "replace-all all matches"
+    (assert= (regexp-replace-all (make-regexp "o") "foo boo" "0") "f00 b00"))
+  (deftest
+    "replace with $& (whole match)"
+    (assert=
+      (regexp-replace (make-regexp "[0-9]+") "price 42" "[$&]")
+      "price [42]"))
+  (deftest
+    "replace-all removes digits"
+    (assert=
+      (regexp-replace-all (make-regexp "[0-9]") "a1b2c3" "")
+      "abc")))
+
+;; --------------------------------------------------------------------------
+;; regexp-split
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:split"
+  (deftest
+    "split on whitespace"
+    (let
+      ((parts (regexp-split (make-regexp " +") "hello world foo")))
+      (assert= (length parts) 3)))
+  (deftest
+    "split first part"
+    (let
+      ((parts (regexp-split (make-regexp ",") "a,b,c")))
+      (assert= (first parts) "a")))
+  (deftest
+    "split last part"
+    (let
+      ((parts (regexp-split (make-regexp ",") "a,b,c")))
+      (assert= (first (rest (rest parts))) "c")))
+  (deftest
+    "split no match → single element"
+    (let
+      ((parts (regexp-split (make-regexp ",") "hello")))
+      (assert= (length parts) 1))))
+
+;; --------------------------------------------------------------------------
+;; flags
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "regexp:flags"
+  (deftest
+    "case-insensitive flag"
+    (let
+      ((m (regexp-match (make-regexp "HELLO" "i") "hello world")))
+      (assert (not (nil? m)))))
+  (deftest
+    "case-sensitive without flag"
+    (assert-nil (regexp-match (make-regexp "HELLO") "hello world")))
+  (deftest
+    "multiline ^ matches line starts"
+    (let
+      ((ms (regexp-match-all (make-regexp "^[a-z]" "m") "a\nb\nc")))
+      (assert= (length ms) 3))))