diff --git a/src/api.ml b/src/api.ml
index 01e37c8b..e4d7e007 100644
--- a/src/api.ml
+++ b/src/api.ml
@@ -1,10 +1,10 @@
 (* TODO
+   option:
+     - correct use opt_mem or Jsont.option
    number
      - number is "float", but we probably want int everywhere instead
      - numeric values capped at 2^53 -1 inclusive because json
-   time
-     - better types
-     - issues with "never" = uint64_max *)
+     *)
 open Crypto
 open Bin_signature
 
@@ -12,6 +12,36 @@ let encode_exn jsont v = Jsont_bytesrw.encode_string jsont v |> Result.get_ok
 let encode jsont v = Jsont_bytesrw.encode_string jsont v
 let decode jsont v = Jsont_bytesrw.decode_string jsont v
 
+module Account_operation = struct
+  type t =
+    | Withdraw
+    | Deposit
+    | Merge
+    | Balance
+    | Close
+    | Aggregate
+    | Transaction
+    | Refund
+
+  let to_string t =
+    String.uppercase_ascii
+    @@
+    match t with
+    | Withdraw -> "withdraw"
+    | Deposit -> "deposit"
+    | Merge -> "merge"
+    | Balance -> "balance"
+    | Close -> "close"
+    | Aggregate -> "aggregate"
+    | Transaction -> "transaction"
+    | Refund -> "refund"
+
+  let jsont =
+    [ Withdraw; Deposit; Merge; Balance; Close; Aggregate; Transaction; Refund ]
+    |> List.map (fun t -> (to_string t, t))
+    |> Jsont.enum ~kind:"account operation type"
+end
+
 module ErrorDetail = struct
   (* TODO GANA error codes
      https://git.gnunet.org/gana.git/tree/gnu-taler-error-codes/registry.rec *)
@@ -26,7 +56,7 @@ module ErrorDetail = struct
     let enc_hint v = v.hint in
     Jsont.Object.map ~kind:"ErrorDetail" make
     |> Jsont.Object.mem "code" Jsont.int ~enc:enc_code
-    |> Jsont.Object.opt_mem "hint" Jsont.(string) ~enc:enc_hint
+    |> Jsont.Object.opt_mem "hint" Jsont.string ~enc:enc_hint
     |> Jsont.Object.finish
 end
 
@@ -1000,7 +1030,8 @@ module RsaDenomGroup = struct
     |> finish
 end
 
-(* TODO better jsont cases
+(* TODO cases
+   better jsont cases handling
    factorize common fields (DenomCommon/DenomGroupCommon)
    "+age_restricted"/CS variants
    raise error not implemented if not RSA *)
@@ -1018,3 +1049,28 @@ module DenomGroup = struct
     |> case_mem "cipher" Jsont.string ~enc:Fun.id ~enc_case cases
     |> finish
 end
+
+module AccountLimit = struct
+  type t = {
+    operation_type: Account_operation.t;
+    timeframe: RelativeTime.t;
+    threshold: Amount.t;
+    soft_limit: bool option;
+  }
+
+  let jsont =
+    let make operation_type timeframe threshold soft_limit =
+      { operation_type; timeframe; threshold; soft_limit }
+    in
+    let operation_type v = v.operation_type in
+    let timeframe v = v.timeframe in
+    let threshold v = v.threshold in
+    let soft_limit v = v.soft_limit in
+    let open Jsont.Object in
+    map ~kind:"AccountLimit" make
+    |> mem "operation_type" Account_operation.jsont ~enc:operation_type
+    |> mem "timeframe" RelativeTime.jsont ~enc:timeframe
+    |> mem "threshold" Amount.jsont ~enc:threshold
+    |> opt_mem "soft_limit" Jsont.bool ~enc:soft_limit
+    |> finish
+end