diff --git a/.ocamlformat b/.ocamlformat
index 0b4add55..4823e7af 100644
--- a/.ocamlformat
+++ b/.ocamlformat
@@ -1,6 +1,7 @@
 version=0.27.0
 exp-grouping=preserve
-break-infix=wrap-or-vertical
+type-decl=sparse
+break-infix=fit-or-vertical
 break-collection-expressions=wrap
 break-sequences=false
 break-infix-before-func=false
diff --git a/src/assets.ml b/src/assets.ml
index 5116e366..4ec1b634 100644
--- a/src/assets.ml
+++ b/src/assets.ml
@@ -8,7 +8,9 @@
    https://docs.taler.net/design-documents/003-tos-rendering.html *)
 
 (* todo: maybe move this type to config.ml *)
-type t = Terms | Privacy
+type t =
+  | Terms
+  | Privacy
 
 let etag = function
   | Terms -> Config.terms_etag
diff --git a/src/config.ml b/src/config.ml
index f5b0b0a8..304788ae 100644
--- a/src/config.ml
+++ b/src/config.ml
@@ -26,7 +26,11 @@ let currency_to_string = function `Eur -> "EUR"
 
 (* Values that represent an amount are in the usual amount syntax: CURRENCY:VALUE.FRACTION,
    e.g. EUR:1.50. The FRACTION portion may extend up to 8 places. *)
-type value = { currency: [ `Eur ]; value: int; fraction: int }
+type value = {
+    currency: [ `Eur ]
+  ; value: int
+  ; fraction: int
+}
 
 let currency_round_unit = { currency= `Eur; value= 0; fraction= 1 }
 
diff --git a/src/headers_lib.ml b/src/headers_lib.ml
index c54081b4..357b9d0b 100644
--- a/src/headers_lib.ml
+++ b/src/headers_lib.ml
@@ -20,8 +20,14 @@ end = struct
   type t = string
 
   (* type for the value of header field *)
-  type header_etag_item = { weak: bool; value: string }
-  type header_value = Any_etag | Etag_list of header_etag_item list
+  type header_etag_item = {
+      weak: bool
+    ; value: string
+  }
+
+  type header_value =
+    | Any_etag
+    | Etag_list of header_etag_item list
 
   let pp_header_etag_item ppf { weak; value } =
     if weak then Fmt.pf ppf {|W/"%s"|} value else Fmt.pf ppf {|"%s"|} value
diff --git a/src/types.ml b/src/types.ml
index d2406dec..e9903a99 100644
--- a/src/types.ml
+++ b/src/types.ml
@@ -2,14 +2,32 @@
 module Error_detail = struct
   (* TODO GANA error codes
      https://git.gnunet.org/gana.git/tree/gnu-taler-error-codes/registry.rec *)
-  type t = { code: int; hint: string option }
+  type t = {
+      code: int
+    ; hint: string option
+  }
 end
 
+(* TODO number
+   - number is "float", but we probably want int everywhere instead
+   - numeric values capped at 2^53 -1 inclusive because json
+   - have a type for seconds/microseconds/..? *)
 module Timestamp = struct
   (* Seconds since epoch, or the special
      value "never" to represent an event that will
      never happen. *)
-  type t = Never | Seconds of float
+  type t =
+    | Seconds of float
+    | Never
+end
+
+module Relative_time = struct
+  (* Duration in microseconds or "forever"
+     to represent an infinite duration. Numeric
+     values are capped at 2^53 - 1 inclusive. *)
+  type t =
+    | Microseconds of float
+    | Forever
 end
 
 module Amount = struct