diff --git a/README.md b/README.md
index 6aec3f7..f6e2acd 100644
--- a/README.md
+++ b/README.md
@@ -9,9 +9,9 @@ opam install . --deps-only --with-test
 ## Run
 
 ```
-dune exec aoc -- --help
-dune exec aoc -- --day 1 --part 1
-dune exec aoc -- -d1 -p1
+dune exec aoc -- -help
+dune exec aoc -- -day 1 -part 1
+dune exec aoc -- -d 1 -p 1
 ```
 
 ## Build
diff --git a/aoc.opam b/aoc.opam
index 8c22df5..89630ac 100644
--- a/aoc.opam
+++ b/aoc.opam
@@ -11,7 +11,7 @@ depends: [
   "dune" {>= "3.10"}
   "angstrom"
   "core"
-  "cmdliner"
+  "core_unix"
   "ppx_jane"
   "re"
   "odoc" {with-doc}
diff --git a/aoc.opam.locked b/aoc.opam.locked
index 899b64f..90d795c 100644
--- a/aoc.opam.locked
+++ b/aoc.opam.locked
@@ -9,8 +9,8 @@ homepage: "https://github.com/drewolson/aoc-ocaml"
 bug-reports: "https://github.com/drewolson/aoc-ocaml/issues"
 depends: [
   "angstrom" {= "0.15.0"}
-  "cmdliner" {= "1.2.0"}
   "core" {= "v0.16.2"}
+  "core_unix" {= "v0.16.0"}
   "dune" {= "3.11.1"}
   "ocaml" {= "5.1.0"}
   "ppx_jane" {= "v0.16.0"}
diff --git a/bin/dune b/bin/dune
index e0e8e49..709e708 100644
--- a/bin/dune
+++ b/bin/dune
@@ -3,7 +3,10 @@
   (name main)
   (libraries
     core
-    cmdliner
+    core_unix.command_unix
     runner)
+  (preprocess
+    (pps
+     ppx_jane))
   (flags
     -open Core))
diff --git a/bin/main.ml b/bin/main.ml
index be2799d..cbbbcbb 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -1,36 +1,39 @@
-module Arg = Cmdliner.Arg
-module Cmd = Cmdliner.Cmd
-module Term = Cmdliner.Term
-
-let ( & ), ( $ ) = Arg.(( & )), Cmdliner.Term.(( $ ))
-
-let year =
-  let doc = "Year to run" in
-  Arg.value & Arg.opt Arg.int 2022 & Arg.info [ "y"; "year" ] ~docv:"YEAR" ~doc
+let year_arg =
+  Command.Arg_type.create (fun year_str ->
+    match Int.of_string_opt year_str with
+    | Some year when year = 2022 || year = 2023 -> year
+    | _ -> failwith "Year must be [2022, 2023]")
 ;;
 
-let day =
-  let doc = "Day to run (1 - 25)" in
-  let days = List.map ~f:(fun d -> Int.to_string d, d) (List.init 25 ~f:Int.succ) in
-  Arg.required
-  & Arg.opt (Arg.some & Arg.enum days) None
-  & Arg.info [ "d"; "day" ] ~docv:"DAY" ~doc
+let day_arg =
+  Command.Arg_type.create (fun day_str ->
+    match Int.of_string_opt day_str with
+    | Some day when 1 <= day && day <= 25 -> day
+    | _ -> failwith "Day must be between 1 - 25")
 ;;
 
-let part =
-  let doc = "Part to run (1 or 2)" in
-  let parts = [ "1", 1; "2", 2 ] in
-  Arg.required
-  & Arg.opt (Arg.some & Arg.enum parts) None
-  & Arg.info [ "p"; "part" ] ~docv:"PART" ~doc
+let part_arg =
+  Command.Arg_type.create (fun part_str ->
+    match Int.of_string_opt part_str with
+    | Some part when part = 1 || part = 2 -> part
+    | _ -> failwith "Part must be 1 or 2")
 ;;
 
-let aoc_t = Term.const Runner.run $ year $ day $ part
-
-let cmd =
-  let doc = "Run aoc solution" in
-  let info = Cmd.info "aoc" ~version:"1.0.0" ~doc in
-  Cmd.v info aoc_t
+let command_param =
+  let open Command.Let_syntax in
+  let module P = Command.Param in
+  let%map year =
+    P.flag
+      "year"
+      (P.optional_with_default 2022 year_arg)
+      ~doc:"int year to run (default: 2022)"
+      ~aliases:[ "y" ]
+  and day =
+    P.flag "day" (P.required day_arg) ~aliases:[ "d" ] ~doc:"int day to run (1 - 25)"
+  and part =
+    P.flag "part" (P.required part_arg) ~aliases:[ "p" ] ~doc:"int part to run (1 or 2)"
+  in
+  fun _ -> Runner.run year day part
 ;;
 
-let () = Stdlib.exit (Cmd.eval cmd)
+let () = Command_unix.run (Command.basic command_param ~summary:"Run aoc solution")
diff --git a/dune-project b/dune-project
index ad036fb..72d2bfd 100644
--- a/dune-project
+++ b/dune-project
@@ -22,6 +22,6 @@
 
     angstrom
     core
-    cmdliner
+    core_unix
     ppx_jane
     re))
diff --git a/lib/runner/dune b/lib/runner/dune
index 8444f19..183dad5 100644
--- a/lib/runner/dune
+++ b/lib/runner/dune
@@ -4,5 +4,8 @@
     core
     year2022
     year2023)
+  (preprocess
+    (pps
+     ppx_jane))
   (flags
     -open Core))
diff --git a/lib/util/list.mli b/lib/util/list.mli
deleted file mode 100644
index 0c40c99..0000000
--- a/lib/util/list.mli
+++ /dev/null
@@ -1,3 +0,0 @@
-val max_int : int list -> int
-val sum_int : int list -> int
-val take : int -> 'a list -> 'a list
diff --git a/lib/util/parser.ml b/lib/util/parser.ml
index a6fc15b..59c7b57 100644
--- a/lib/util/parser.ml
+++ b/lib/util/parser.ml
@@ -1,27 +1,34 @@
-module A = Angstrom
+include Angstrom
 
 module Syntax = struct
-  module Let_syntax = A.Let_syntax.Let_syntax
+  module Let_syntax = Angstrom.Let_syntax.Let_syntax
 
-  let ( let+ ) = A.( let+ )
-  let ( and+ ) = A.( and+ )
-  let ( let* ) = A.( let* )
+  let ( let+ ) = ( let+ )
+  let ( and+ ) = ( and+ )
+  let ( let* ) = ( let* )
 
   let ( >>| ), ( *> ), ( <* ), ( <|> ), ( <$> ) =
-    A.(( >>| ), ( *> ), ( <* ), ( <|> ), ( <$> ))
+    ( >>| ), ( *> ), ( <* ), ( <|> ), ( <$> )
   ;;
 
   let ( $> ) p a = p >>| const a
   let ( <$ ) a p = p >>| const a
 end
 
-open Syntax
-
-let integerP =
+let integer =
+  let open Syntax in
   let%map tokens =
-    A.take_while1 (function
+    take_while1 (function
       | '0' .. '9' -> true
       | _ -> false)
   in
   Int.of_string tokens
 ;;
+
+let parse_exn parser input =
+  input |> parse_string ~consume:Prefix parser |> Result.ok_or_failwith
+;;
+
+let parse_all_exn parser input =
+  input |> parse_string ~consume:All parser |> Result.ok_or_failwith
+;;
diff --git a/lib/util/parser.mli b/lib/util/parser.mli
deleted file mode 100644
index 103d45a..0000000
--- a/lib/util/parser.mli
+++ /dev/null
@@ -1,20 +0,0 @@
-module A = Angstrom
-
-module Syntax : sig
-  module Let_syntax : sig
-    include module type of A.Let_syntax.Let_syntax
-  end
-
-  val ( let+ ) : 'a A.t -> ('a -> 'b) -> 'b A.t
-  val ( and+ ) : 'a A.t -> 'b A.t -> ('a * 'b) A.t
-  val ( let* ) : 'a A.t -> ('a -> 'b A.t) -> 'b A.t
-  val ( *> ) : 'a A.t -> 'b A.t -> 'b A.t
-  val ( <* ) : 'a A.t -> 'b A.t -> 'a A.t
-  val ( >>| ) : 'a A.t -> ('a -> 'b) -> 'b A.t
-  val ( <$> ) : ('a -> 'b) -> 'a A.t -> 'b A.t
-  val ( <|> ) : 'a A.t -> 'a A.t -> 'a A.t
-  val ( $> ) : 'a A.t -> 'b -> 'b A.t
-  val ( <$ ) : 'b -> 'a A.t -> 'b A.t
-end
-
-val integerP : int A.t
diff --git a/lib/year2022/day04.ml b/lib/year2022/day04.ml
index f071248..c7deaed 100644
--- a/lib/year2022/day04.ml
+++ b/lib/year2022/day04.ml
@@ -1,5 +1,4 @@
 module P = Util.Parser
-module A = Angstrom
 open P.Syntax
 
 type range =
@@ -7,19 +6,19 @@ type range =
   ; stop : int
   }
 
-let rangeP =
-  let%map start = P.integerP <* A.char '-'
-  and stop = P.integerP in
+let range_p =
+  let%map start = P.integer <* P.char '-'
+  and stop = P.integer in
   { start; stop }
 ;;
 
-let rangePairP =
-  let%map a = rangeP <* A.char ','
-  and b = rangeP in
+let range_pair_p =
+  let%map a = range_p <* P.char ','
+  and b = range_p in
   a, b
 ;;
 
-let rangePairsP = A.sep_by (A.char '\n') rangePairP
+let range_pairs_p = P.sep_by (P.char '\n') range_pair_p
 
 let is_subset a b =
   (a.start <= b.start && a.stop >= b.stop) || (b.start <= a.start && b.stop >= a.stop)
@@ -31,16 +30,14 @@ let is_overlapping a b =
 
 let part1 input =
   input
-  |> A.parse_string ~consume:Prefix rangePairsP
-  |> Result.ok_or_failwith
+  |> P.parse_exn range_pairs_p
   |> List.filter ~f:(fun (a, b) -> is_subset a b)
   |> List.length
 ;;
 
 let part2 input =
   input
-  |> A.parse_string ~consume:Prefix rangePairsP
-  |> Result.ok_or_failwith
+  |> P.parse_exn range_pairs_p
   |> List.filter ~f:(fun (a, b) -> is_overlapping a b)
   |> List.length
 ;;
diff --git a/lib/year2022/day05.ml b/lib/year2022/day05.ml
index e6a0938..343f510 100644
--- a/lib/year2022/day05.ml
+++ b/lib/year2022/day05.ml
@@ -1,5 +1,4 @@
 module P = Util.Parser
-module A = Angstrom
 module IntMap = Map.Make (Int)
 open P.Syntax
 
@@ -16,21 +15,21 @@ type instructions =
   ; crates : crate list IntMap.t
   }
 
-let dropLineP = A.skip_while (fun c -> not (Char.equal c '\n')) <* A.end_of_line
-let noCrateP = None <$ A.string "   "
-let yesCrateP = Option.some <$> A.char '[' *> A.any_char <* A.char ']'
-let crateP = noCrateP <|> yesCrateP
-let crateLineP = A.sep_by1 (A.char ' ') crateP
-let crateLinesP = A.sep_by1 A.end_of_line crateLineP <* A.end_of_line
+let drop_line_p = P.skip_while (fun c -> not (Char.equal c '\n')) <* P.end_of_line
+let no_crate_p = None <$ P.string "   "
+let yes_crate_p = Option.some <$> P.char '[' *> P.any_char <* P.char ']'
+let crate_p = no_crate_p <|> yes_crate_p
+let crate_line_p = P.sep_by1 (P.char ' ') crate_p
+let crate_lines_p = P.sep_by1 P.end_of_line crate_line_p <* P.end_of_line
 
-let moveP =
-  let%map n = A.string "move " *> P.integerP
-  and from = A.string " from " *> P.integerP
-  and to' = A.string " to " *> P.integerP in
+let move_p =
+  let%map n = P.string "move " *> P.integer
+  and from = P.string " from " *> P.integer
+  and to' = P.string " to " *> P.integer in
   { n; from; to' }
 ;;
 
-let movesP = A.sep_by1 A.end_of_line moveP
+let moves_p = P.sep_by1 P.end_of_line move_p
 
 let pad_crates crates =
   let max = crates |> List.map ~f:List.length |> Util.List.max_int in
@@ -48,10 +47,10 @@ let to_stacks crates =
   |> IntMap.of_alist_exn
 ;;
 
-let instructionsP =
-  let%map crateLines = crateLinesP <* dropLineP <* dropLineP
-  and moves = movesP in
-  let crates = to_stacks crateLines in
+let instructions_p =
+  let%map crate_lines = crate_lines_p <* drop_line_p <* drop_line_p
+  and moves = moves_p in
+  let crates = to_stacks crate_lines in
   { moves; crates }
 ;;
 
@@ -63,9 +62,7 @@ let move_crate f crates { n; from; to' } =
 ;;
 
 let find_crates f input =
-  let { moves; crates } =
-    input |> A.parse_string ~consume:Prefix instructionsP |> Result.ok_or_failwith
-  in
+  let { moves; crates } = P.parse_exn instructions_p input in
   moves
   |> List.fold ~init:crates ~f:(move_crate f)
   |> Map.data
diff --git a/lib/year2022/day07.ml b/lib/year2022/day07.ml
index e7c0044..f263b2c 100644
--- a/lib/year2022/day07.ml
+++ b/lib/year2022/day07.ml
@@ -1,5 +1,4 @@
 module P = Util.Parser
-module A = Angstrom
 open P.Syntax
 
 type cmd =
@@ -12,32 +11,32 @@ type fs =
   | File of string * int
   | Dir of string * fs list
 
-let nameP =
-  A.take_while (function
+let name_p =
+  P.take_while (function
     | 'a' .. 'z' | '.' | '/' -> true
     | _ -> false)
 ;;
 
-let cdP =
-  let%map dir = A.string "$ cd " *> nameP in
+let cd_p =
+  let%map dir = P.string "$ cd " *> name_p in
   Cd dir
 ;;
 
-let lsP = Ls <$ A.string "$ ls"
+let ls_p = Ls <$ P.string "$ ls"
 
-let dirItemP =
-  let%map dir = A.string "dir " *> nameP in
+let dir_item_p =
+  let%map dir = P.string "dir " *> name_p in
   DirItem dir
 ;;
 
-let fileItemP =
-  let%map size = P.integerP <* A.char ' '
-  and file = nameP in
+let file_item_p =
+  let%map size = P.integer <* P.char ' '
+  and file = name_p in
   FileItem (size, file)
 ;;
 
-let cmdP = A.choice [ cdP; lsP; dirItemP; fileItemP ]
-let cmdsP = A.sep_by1 A.end_of_line cmdP
+let cmd_p = P.choice [ cd_p; ls_p; dir_item_p; file_item_p ]
+let cmds_p = P.sep_by1 P.end_of_line cmd_p
 
 let build_fs cmds =
   let rec build_nodes nodes = function
@@ -71,8 +70,7 @@ let sizes fs =
 
 let part1 input =
   input
-  |> A.parse_string ~consume:Prefix cmdsP
-  |> Result.ok_or_failwith
+  |> P.parse_exn cmds_p
   |> build_fs
   |> sizes
   |> List.filter ~f:(fun x -> x <= 100000)
@@ -80,13 +78,7 @@ let part1 input =
 ;;
 
 let part2 input =
-  let ns =
-    input
-    |> A.parse_string ~consume:Prefix cmdsP
-    |> Result.ok_or_failwith
-    |> build_fs
-    |> sizes
-  in
+  let ns = input |> P.parse_exn cmds_p |> build_fs |> sizes in
   let goal = 30000000 - (70000000 - List.hd_exn ns) in
   ns |> List.tl_exn |> List.sort ~compare |> List.find_exn ~f:(fun n -> n >= goal)
 ;;