diff --git a/src/util/Sidekick_util.ml b/src/util/Sidekick_util.ml
index fda8f3a4..d1509ab4 100644
--- a/src/util/Sidekick_util.ml
+++ b/src/util/Sidekick_util.ml
@@ -24,5 +24,6 @@ module Hash = Hash
 module Profile = Profile
 module Chunk_stack = Chunk_stack
 module Ser_value = Ser_value
+module Ser_decode = Ser_decode
 
 let[@inline] ( let@ ) f x = f x
diff --git a/src/util/ser_decode.ml b/src/util/ser_decode.ml
new file mode 100644
index 00000000..17b00881
--- /dev/null
+++ b/src/util/ser_decode.ml
@@ -0,0 +1,149 @@
+open struct
+  module Error_ = Error
+  module Fmt = CCFormat
+  module V = Ser_value
+end
+
+module Error = struct
+  type t = { msg: string; v: V.t; subs: t list }
+
+  let mk ?(subs = []) msg v : t = { msg; v; subs }
+
+  let pp out (self : t) =
+    let rec pp out self =
+      Fmt.fprintf out "@[<v2>@[<2>%s@ in %a@]" self.msg V.pp self.v;
+      List.iter
+        (fun s -> Fmt.fprintf out "@ @[<2>sub-error:@ %a@]" pp s)
+        self.subs;
+      Fmt.fprintf out "@]"
+    in
+    Fmt.fprintf out "@[<2>Ser_decode.error:@ %a@]" pp self
+
+  let to_string = Fmt.to_string pp
+end
+
+exception Fail of Error.t
+
+type 'a t = { deser: V.t -> 'a } [@@unboxed]
+
+let[@inline] fail_ msg v = raise_notrace (Fail (Error.mk msg v))
+let[@inline] fail_e e = raise_notrace (Fail e)
+let return x = { deser = (fun _ -> x) }
+let fail s = { deser = (fun v -> fail_ s v) }
+let any = { deser = (fun v -> v) }
+
+let bool =
+  {
+    deser =
+      (function
+      | V.Bool b -> b
+      | v -> fail_ "expected bool" v);
+  }
+
+let int =
+  {
+    deser =
+      (function
+      | V.Int i -> i
+      | v -> fail_ "expected int" v);
+  }
+
+let string =
+  {
+    deser =
+      (function
+      | V.Str s | V.Bytes s -> s
+      | v -> fail_ "expected string" v);
+  }
+
+let list d =
+  {
+    deser =
+      (function
+      | V.List l -> List.map (fun x -> d.deser x) l
+      | v -> fail_ "expected list" v);
+  }
+
+let dict_field name d =
+  {
+    deser =
+      (function
+      | V.Dict m as v ->
+        (match Util.Str_map.find_opt name m with
+        | None -> fail_ (Printf.sprintf "did not find key %S" name) v
+        | Some x -> d.deser x)
+      | v -> fail_ "expected dict" v);
+  }
+
+let dict_field_opt name d =
+  {
+    deser =
+      (function
+      | V.Dict m ->
+        (match Util.Str_map.find_opt name m with
+        | None -> None
+        | Some x -> Some (d.deser x))
+      | v -> fail_ "expected dict" v);
+  }
+
+let both a b =
+  {
+    deser =
+      (fun v ->
+        let xa = a.deser v in
+        let xb = b.deser v in
+        xa, xb);
+  }
+
+let ( >>= ) d f =
+  {
+    deser =
+      (fun v ->
+        let x = d.deser v in
+        (f x).deser v);
+  }
+
+let ( >|= ) d f =
+  {
+    deser =
+      (fun v ->
+        let x = d.deser v in
+        f x);
+  }
+
+let try_l l =
+  {
+    deser =
+      (fun v ->
+        let subs = ref [] in
+        match
+          CCList.find_map
+            (fun d ->
+              match d.deser v with
+              | x -> Some x
+              | exception Fail err ->
+                subs := err :: !subs;
+                None)
+            l
+        with
+        | Some x -> x
+        | None -> fail_e (Error.mk "all decoders failed" v ~subs:!subs));
+  }
+
+module Infix = struct
+  let ( >>= ) = ( >>= )
+  let ( >|= ) = ( >|= )
+  let ( and+ ) = both
+  let ( and* ) = both
+  let ( let+ ) = ( >|= )
+  let ( let* ) = ( >>= )
+end
+
+include Infix
+
+let run d v = try Ok (d.deser v) with Fail err -> Error err
+
+let run_exn d v =
+  try d.deser v
+  with Fail err ->
+    Error_.errorf "ser_decode: failed to decode:@ %a" Error.pp err
diff --git a/src/util/ser_decode.mli b/src/util/ser_decode.mli
new file mode 100644
index 00000000..b5086920
--- /dev/null
+++ b/src/util/ser_decode.mli
@@ -0,0 +1,44 @@
+(** Decoders for {!Ser_value}.
+
+    Combinators to decode values. *)
+
+type +'a t
+(** Decode a value of type ['a] *)
+
+val int : int t
+val bool : bool t
+val string : string t
+val return : 'a -> 'a t
+val fail : string -> 'a t
+val any : Ser_value.t t
+val list : 'a t -> 'a list t
+val dict_field : string -> 'a t -> 'a t
+val dict_field_opt : string -> 'a t -> 'a option t
+val both : 'a t -> 'b t -> ('a * 'b) t
+val try_l : 'a t list -> 'a t
+
+module Infix : sig
+  val ( >|= ) : 'a t -> ('a -> 'b) -> 'b t
+  val ( >>= ) : 'a t -> ('a -> 'b t) -> 'b t
+  val ( let+ ) : 'a t -> ('a -> 'b) -> 'b t
+  val ( and+ ) : 'a t -> 'b t -> ('a * 'b) t
+  val ( let* ) : 'a t -> ('a -> 'b t) -> 'b t
+  val ( and* ) : 'a t -> 'b t -> ('a * 'b) t
+end
+
+include module type of Infix
+
+(** {2 Deserializing} *)
+
+module Error : sig
+  type t
+
+  include Sidekick_sigs.PRINT with type t := t
+
+  val to_string : t -> string
+end
+
+val run : 'a t -> Ser_value.t -> ('a, Error.t) result
+
+val run_exn : 'a t -> Ser_value.t -> 'a
+(** @raise Error.Error in case of failure *)