diff --git a/tools/dune b/tools/dune
new file mode 100644
index 000000000..63b25f432
--- /dev/null
+++ b/tools/dune
@@ -0,0 +1,5 @@
+(executable
+ (name runner)
+ (public_name runner)
+ (package multicoretests)
+ (libraries unix))
diff --git a/tools/runner.ml b/tools/runner.ml
new file mode 100644
index 000000000..9df1737e9
--- /dev/null
+++ b/tools/runner.ml
@@ -0,0 +1,131 @@
+(* Custom runner for the tests so that:
+   - error codes on Windows are turned back into their Unix meaninrgs
+   - anchors are added to CI logs with relevant information *)
+
+let use_github_anchors = Sys.getenv_opt "CI" = Some "true"
+
+let signals =
+  let open Sys in
+  [
+    (sigabrt, "ABRT");
+    (sigalrm, "ALRM");
+    (sigfpe, "FPE");
+    (sighup, "HUP");
+    (sigill, "ILL");
+    (sigint, "INT");
+    (sigkill, "KILL");
+    (sigpipe, "PIPE");
+    (sigquit, "QUIT");
+    (sigsegv, "SEGV");
+    (sigterm, "TERM");
+    (sigusr1, "USR1");
+    (sigusr2, "USR2");
+    (sigchld, "CHLD");
+    (sigcont, "CONT");
+    (sigstop, "STOP");
+    (sigtstp, "TSTP");
+    (sigttin, "TTIN");
+    (sigttou, "TTOU");
+    (sigvtalrm, "VTALRM");
+    (sigprof, "PROF");
+    (sigbus, "BUS");
+    (sigpoll, "POLL");
+    (sigsys, "SYS");
+    (sigtrap, "TRAP");
+    (sigurg, "URG");
+    (sigxcpu, "XCPU");
+    (sigxfsz, "XFSZ");
+  ]
+
+let error fmt cmd msg =
+  if use_github_anchors then
+    Format.fprintf fmt "\n::error title=%s in %s::%s in %s\n%!" msg cmd msg cmd
+  else Format.fprintf fmt "\nError: %s in %s\n%!" msg cmd
+
+let pp_status_unix fmt cmd status =
+  let open Unix in
+  (match status with
+  | WEXITED 0 -> ()
+  | WEXITED s -> error fmt cmd (Printf.sprintf "Exit %d" s)
+  | WSIGNALED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Signal " ^ signal
+        | None -> Printf.sprintf "Unknown signal %d" s
+      in
+      error fmt cmd msg
+  | WSTOPPED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Stop with signal " ^ signal
+        | None -> Printf.sprintf "Stop with unknown signal %d" s
+      in
+      error fmt cmd msg);
+  status = WEXITED 0
+
+(* Under Windows, there is no such thing as terminating due to a
+   signal, so the WSIGNALED and WSTOPPED cases are dead code.
+
+   The strategy is to use conventional exit values (which are 32-bit,
+   not just 8-bit like on Unix) to describe the cause.
+   The documentation of ”NTSTATUS Values” list {e many} cases, too
+   many to handle them all. This is where the value akin to SEGV comes
+   from. Other special cases will be caught as they appear.
+
+   The value used to match ABRT comes from the code of the abort
+   function in the standard library.
+
+   {{:https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-erref/596a1078-e883-4972-9bbc-49e60bebca55}NTSTATUS Values}
+*)
+let pp_status_win fmt cmd status =
+  let open Unix in
+  (match status with
+  | WEXITED 0 -> ()
+  | WEXITED 3 -> error fmt cmd "Signal ABRT"
+  | WEXITED -1073741819 (* 0xC0000005 *) -> error fmt cmd "Signal SEGV"
+  | WEXITED s -> error fmt cmd (Printf.sprintf "Exit %d" s)
+  (* Those last 2 cases are dead code on Windows *)
+  | WSIGNALED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Signal " ^ signal
+        | None -> Printf.sprintf "Unknown signal %d" s
+      in
+      error fmt cmd msg
+  | WSTOPPED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Stop with signal " ^ signal
+        | None -> Printf.sprintf "Stop with unknown signal %d" s
+      in
+      error fmt cmd msg);
+  status = WEXITED 0
+
+let pp_status = if Sys.win32 then pp_status_win else pp_status_unix
+
+let run ofmt efmt argv =
+  let argv =
+    match argv with [| cmd |] -> [| cmd; "--verbose" |] | _ -> argv
+  in
+  let testdir = Filename.basename (Sys.getcwd ()) in
+  let exe, cmd =
+    if Filename.is_implicit argv.(0) then
+      ( Filename.concat Filename.current_dir_name argv.(0),
+        Filename.concat testdir argv.(0) )
+    else (argv.(0), argv.(0))
+  in
+  let cmdline = String.concat " " (Array.to_list argv) in
+  Format.fprintf ofmt "\n\nStarting (in %s) %s:\n%!" testdir cmdline;
+  let pid = Unix.(create_process exe argv stdin stdout stderr) in
+  let _, status = Unix.waitpid [] pid in
+  pp_status efmt cmd status
+
+let _ =
+  let open Format in
+  if Array.length Sys.argv < 2 then (
+    fprintf err_formatter
+      "\nError: %s expects the\n  command to run as argument\n%!" Sys.argv.(0);
+    exit 1);
+  let cmd = Array.sub Sys.argv 1 (Array.length Sys.argv - 1) in
+  let success = run std_formatter err_formatter cmd in
+  if not success then exit 1