diff --git a/src/cbor/containers_cbor.ml b/src/cbor/containers_cbor.ml
new file mode 100644
index 00000000..f1ac5eed
--- /dev/null
+++ b/src/cbor/containers_cbor.ml
@@ -0,0 +1,290 @@
+
+module Fmt = CCFormat
+
+type t =
+  [ `Null
+  | `Undefined
+  | `Simple of int
+  | `Bool of bool
+  | `Int of int
+  | `Float of float
+  | `Bytes of string
+  | `Text of string
+  | `Array of t list
+  | `Map of (t * t) list
+  | `Tag of int * t
+  ]
+
+let rec pp_diagnostic out (self:t) =
+  match self with
+  | `Null -> Fmt.string out "null"
+  | `Undefined -> Fmt.string out "undefined"
+  | `Simple i -> Fmt.fprintf out "simple(%d)" i
+  | `Bool b -> Fmt.bool out b
+  | `Int i -> Fmt.int out i
+  | `Float f -> Fmt.float out f
+  | `Bytes b -> Fmt.fprintf out "h'%s'" (CCString.to_hex b)
+  | `Text s -> Fmt.fprintf out "%S" s
+  | `Array l ->
+    Fmt.fprintf out "[@[";
+    List.iteri
+      (fun i x ->
+        if i>0  then Fmt.fprintf out ",@ ";
+        pp_diagnostic out x) l;
+    Fmt.fprintf out "@]]"
+  | `Map l ->
+    Fmt.fprintf out "{@[";
+    List.iteri
+      (fun i (k,v) ->
+        if i>0  then Fmt.fprintf out "m@ ";
+        Fmt.fprintf out "@[%a:@ %a@]" pp_diagnostic k pp_diagnostic v) l;
+    Fmt.fprintf out "@}]"
+  | `Tag (i,x) -> Fmt.fprintf out "%d(@[%a@])" i pp_diagnostic x
+
+(* we use funtions from Bytes *)
+[@@@ifge 4.08]
+
+exception Indefinite
+
+let decode_exn (s:string) : t =
+  let b = Bytes.unsafe_of_string s in
+  let i = ref 0 in
+
+  (* currently at end delimiter? *)
+  let[@inline] is_break_stop_code () =
+    Char.code s.[!i] = 0b111_11111
+  in
+
+  let[@inline] read_i8 () =
+    let c = Char.code s.[!i] in
+    incr i;
+    c
+  in
+
+  let[@inline] read_i16 () =
+    let c = Bytes.get_uint16_be b !i in
+    i := !i + 2;
+    c
+  in
+
+  let[@inline] read_i32 () =
+    let c = Bytes.get_int32_be b !i in
+    i := !i + 4;
+    c
+  in
+
+  let[@inline] read_i64 () =
+    let c = Bytes.get_int64_be b !i in
+    i := !i + 8;
+    c
+  in
+
+  let reserve_n n =
+    let j = !i in
+    if j + n >= String.length s then failwith "cbor: cannot extract slice";
+    i := !i + n;
+    j
+  in
+
+  let[@inline] i64_to_int i =
+    let j = Int64.to_int i in
+    if Int64.(of_int j = i) then j
+    else failwith "int64 does not fit in int"
+  in
+
+  (* read integer value from least significant bits *)
+  let read_int ~allow_indefinite low =
+    match low with
+    | _ when low < 0 -> failwith "cbor: invalid length"
+    | _ when low < 24 -> Int64.of_int low
+    | 24 -> Int64.of_int (read_i8())
+    | 25 -> Int64.of_int (read_i16())
+    | 26 -> Int64.of_int32 (read_i32())
+    | 27 -> read_i64()
+    | 28 | 29 | 30 -> failwith "cbor: invalid length"
+    | 31 ->
+      if allow_indefinite then raise_notrace Indefinite
+      else failwith "cbor: invalid integer 31 in this context"
+    | _ -> assert false
+  in
+
+  (* roughly follow https://www.rfc-editor.org/rfc/rfc8949.html#pseudocode *)
+  let rec read_value () =
+    let c = read_i8() in
+    let high = c land 0b111_00000 in
+    let low  = c land 0b000_11111 in
+    begin match high with
+      | 0 -> `Int (read_int ~allow_indefinite:false low |> i64_to_int)
+      | 1 ->
+        let i = read_int ~allow_indefinite:false low |> i64_to_int in
+        `Int (-1 - i)
+      | 2 ->
+        let s = read_bytes ~ty:`Bytes low in
+        `Bytes s
+      | 3 ->
+        let s = read_bytes ~ty:`String low in
+        `Text s
+
+      | 4 ->
+        let l =
+          match read_int ~allow_indefinite:true low |> i64_to_int with
+          | len -> List.init len (fun _ -> read_value())
+          | exception Indefinite ->
+            let l = ref [] in
+            while not (is_break_stop_code ()) do
+              l := read_value() :: !l
+            done;
+            incr i; (* consume stop code *)
+            List.rev !l
+        in
+        `Array l
+
+      | 5 ->
+        let l =
+          match read_int ~allow_indefinite:true low |> i64_to_int with
+          | len -> List.init len (fun _ -> read_pair())
+          | exception Indefinite ->
+            let l = ref [] in
+            while not (is_break_stop_code ()) do
+              l := read_pair() :: !l
+            done;
+            incr i; (* consume stop code *)
+            List.rev !l
+        in
+        `Map l
+
+      | 6 ->
+        let tag = read_int ~allow_indefinite:false low |> i64_to_int in
+        let v = read_value() in
+        `Tag (tag,v)
+
+      | 7 ->
+        (* simple or float,
+           https://www.rfc-editor.org/rfc/rfc8949.html#fpnocont *)
+        let i = read_int ~allow_indefinite:false low in
+        begin match low with
+          | 20 -> `Bool false
+          | 21 -> `Bool true
+          | 22 -> `Null
+          | 23 -> `Undefined
+          | _ when low<=24 -> `Simple (i64_to_int i)
+          | 25 -> (* float16 *)
+            assert false (* TODO *)
+          | 26 -> (* float 32 *)
+            `Float (Int32.float_of_bits (Int64.to_int32 i))
+          | 27 -> (* float 64 *)
+            `Float (Int64.float_of_bits i)
+          | 28 | 29 | 30 -> failwith "cbor: malformed"
+          | 31 -> failwith "uncaught 'break' stop code"
+          | _ -> assert false (* unreachable *)
+        end
+
+      | _ -> assert false (* unreachable *)
+    end
+
+    and read_bytes ~ty low =
+      match read_int ~allow_indefinite:true low |> i64_to_int with
+      | exception Indefinite ->
+        let buf = Buffer.create 32 in
+        while not (is_break_stop_code()) do
+          match read_value(), ty with
+          | `Text s, `String
+          | `Bytes s, `Bytes -> Buffer.add_string buf s
+          | _ -> failwith "cbor: invalid chunk in indefinite length string/byte"
+        done;
+        incr i; (* consume stop code *)
+        Buffer.contents buf
+      | len ->
+        let off = reserve_n len in
+        String.sub s off len
+
+    and read_pair() =
+      let k = read_value() in
+      let v = read_value() in
+      k,v
+  in
+  read_value()
+
+let decode s =
+  try Ok (decode_exn s)
+  with Failure s -> Error s
+
+let encode ?(buf=Buffer.create 32) (self:t) : string =
+  Buffer.clear buf;
+
+  let[@inline] add_byte (high:int) (low:int) =
+    let i = (high lsl 5) lor low in
+    assert ((i land 0xff) == i);
+    Buffer.add_char buf (Char.unsafe_chr i)
+  in
+
+  let add_i64 (i:int64) =
+    Buffer.add_int64_be buf i
+  in
+
+  (* add unsigned integer, including first tag byte *)
+  let add_uint (high:int) (x:int) =
+    assert (x >= 0);
+    if x <= 24 then add_byte high x
+    else if x <= 0xff then (
+      add_byte high 24;
+      Buffer.add_char buf (Char.unsafe_chr x)
+    ) else if x <= 0xff_ff then (
+      add_byte high 25;
+      Buffer.add_uint16_be buf x
+    ) else if x <= 0xff_ff_ff_ff then (
+      add_byte high 26;
+      Buffer.add_int32_be buf (Int32.of_int x)
+    ) else (
+      add_byte high 27;
+      Buffer.add_int64_be buf (Int64.of_int x)
+    )
+  in
+
+  let rec encode_val (self:t): unit =
+    match self with
+    | `Bool false -> add_byte 7 20
+    | `Bool true -> add_byte 7 21
+    | `Null -> add_byte 7 22
+    | `Undefined -> add_byte 7 23
+    | `Simple i ->
+      if i < 24 then add_byte 7 i
+      else if i < 32 then failwith "cbor: simple value in [24, 32["
+      else if i <= 0xff then (
+        add_byte 7 24;
+        Buffer.add_char buf (Char.unsafe_chr i)
+      ) else (
+        failwith "cbor: simple value too high (above 255)"
+      )
+    | `Float f ->
+      add_byte 7 27; (* float 64 *)
+      add_i64 (Int64.bits_of_float f)
+    | `Array l ->
+      add_uint 4 (List.length l);
+      List.iter encode_val l
+    | `Map l ->
+      add_uint 5 (List.length l);
+      List.iter (fun (k,v) -> encode_val k; encode_val v) l
+    | `Text s ->
+      add_uint 3 (String.length s);
+      Buffer.add_string buf s
+    | `Bytes s ->
+      add_uint 4 (String.length s);
+      Buffer.add_string buf s
+    | `Tag (t, v) ->
+      add_uint 6 t;
+      encode_val v
+    | `Int i ->
+      if i >= 0 then add_uint 0 i
+      else if min_int + 2 > i then (
+        (* large negative int, be careful. encode [(-i)-1] via int64. *)
+        add_byte 1 27;
+        Buffer.add_int64_be buf (Int64.(neg (add 1L (of_int i))))
+      ) else (
+        add_uint 1 (-i-1)
+      )
+  in
+  encode_val self;
+  Buffer.contents buf
+
+[@@@endif]
diff --git a/src/cbor/containers_cbor.mli b/src/cbor/containers_cbor.mli
new file mode 100644
index 00000000..99decdbc
--- /dev/null
+++ b/src/cbor/containers_cbor.mli
@@ -0,0 +1,36 @@
+
+(** CBOR encoder/decoder.
+
+  The type is chosen to be compatible with ocaml-cbor.
+  See {{: https://www.rfc-editor.org/rfc/rfc8949.html} the RFC}.
+  *)
+
+type t =
+  [ `Null
+  | `Undefined
+  | `Simple of int
+  | `Bool of bool
+  | `Int of int
+  | `Float of float
+  | `Bytes of string
+  | `Text of string
+  | `Array of t list
+  | `Map of (t * t) list
+  | `Tag of int * t
+  ]
+
+val pp_diagnostic : t CCFormat.printer
+
+(* we use funtions from Bytes *)
+[@@@ifge 4.08]
+
+val encode : ?buf:Buffer.t -> t -> string
+
+val decode : string -> (t, string) result
+
+val decode_exn : string -> t
+(** Like {!decode}.
+    @raise Failure if the string isn't valid *)
+
+
+[@@@endif]
diff --git a/src/cbor/dune b/src/cbor/dune
new file mode 100644
index 00000000..0810df8b
--- /dev/null
+++ b/src/cbor/dune
@@ -0,0 +1,4 @@
+(library
+  (name containers_cbor)
+  (libraries containers)
+  (public_name containers.cbor))