diff --git a/.github/workflows/proof_tools.yml b/.github/workflows/proof_tools.yml
index be40fbefeaa0d3c28c22ec9ed2e84ddf211bf121..d067d83fec6ae3b79f8f6bb81397aa0cb78f968a 100644
--- a/.github/workflows/proof_tools.yml
+++ b/.github/workflows/proof_tools.yml
@@ -28,5 +28,7 @@ jobs:
       run: |
         cd proofs/psnj_toolbox || exit 1
         opam install . --deps-only --yes
+        opam install ocamlformat
+        opam exec -- dune build @fmt
         opam exec -- dune build
         opam exec -- dune test
diff --git a/proofs/psnj_toolbox/bin/main.ml b/proofs/psnj_toolbox/bin/main.ml
index 74810c27b34990050f2dae864c4c64b050e1e5f5..ccf1814f2812a92fed45c2487ac004da70b16059 100644
--- a/proofs/psnj_toolbox/bin/main.ml
+++ b/proofs/psnj_toolbox/bin/main.ml
@@ -13,7 +13,7 @@ let cmds =
     Autosolve.cmd;
     Qfo.cmd;
     Group.cmd;
-    Pipe.cmd
+    Pipe.cmd;
   ]
 
 let () = Term.(exit @@ eval_choice default_cmd cmds)
diff --git a/proofs/psnj_toolbox/pipe_tests/ex/dune b/proofs/psnj_toolbox/pipe_tests/ex/dune
index a02c2cdf2b995f1d4c38bb8fc20de49151299146..ae001bce2537d5eaf7f0dc8d85461db4228bd13a 100644
--- a/proofs/psnj_toolbox/pipe_tests/ex/dune
+++ b/proofs/psnj_toolbox/pipe_tests/ex/dune
@@ -7,4 +7,5 @@
   (glob_files encoding/*)
   (glob_files spec/main.lp))
  (libraries unix)
- (action (run ./ex.exe %{bin:psnj})))
+ (action
+  (run ./ex.exe %{bin:psnj})))
diff --git a/proofs/psnj_toolbox/pipe_tests/ex/ex.ml b/proofs/psnj_toolbox/pipe_tests/ex/ex.ml
index ff49298f935d79bd49cb8a9798a6fc5f01bdd6fa..cb263ff4c2065a6e1f9004640099c5d6807acf0b 100644
--- a/proofs/psnj_toolbox/pipe_tests/ex/ex.ml
+++ b/proofs/psnj_toolbox/pipe_tests/ex/ex.ml
@@ -4,8 +4,8 @@ let () =
       (Filename.quote_command Sys.argv.(1)
          [ "pipe"; "--qfo"; "encoding/qfo.json"; "ex.log" ])
   with
-  | Unix.WEXITED 0 -> 
-      ignore @@ Unix.system (Filename.quote_command "cat" ["exi.lp"])
+  | Unix.WEXITED 0 ->
+      ignore @@ Unix.system (Filename.quote_command "cat" [ "exi.lp" ])
   | Unix.WEXITED n ->
       Format.eprintf "Command exited with code %d@." n;
       exit 1
diff --git a/proofs/psnj_toolbox/pipe_tests/hello/dune b/proofs/psnj_toolbox/pipe_tests/hello/dune
index cfaa9d62072efff6d5ba3e7c8db22d9739736940..507c94ef98086cf16b96788845b220a537a0c419 100644
--- a/proofs/psnj_toolbox/pipe_tests/hello/dune
+++ b/proofs/psnj_toolbox/pipe_tests/hello/dune
@@ -7,4 +7,5 @@
   (glob_files encoding/*)
   (glob_files spec/main.lp))
  (libraries unix)
- (action (run ./hello.exe %{bin:psnj})))
+ (action
+  (run ./hello.exe %{bin:psnj})))
diff --git a/proofs/psnj_toolbox/pipe_tests/hello/hello.ml b/proofs/psnj_toolbox/pipe_tests/hello/hello.ml
index 0a64c40fb310b2014ae0c6171772eec4e7cc6767..939fe02f6bd81f03b1aceebc27f966c828a0f3fd 100644
--- a/proofs/psnj_toolbox/pipe_tests/hello/hello.ml
+++ b/proofs/psnj_toolbox/pipe_tests/hello/hello.ml
@@ -5,7 +5,7 @@ let () =
          [ "pipe"; "--qfo"; "encoding/qfo.json"; "hello.log" ])
   with
   | Unix.WEXITED 0 ->
-      ignore (Unix.system (Filename.quote_command "cat" ["hello.lp"]))
+      ignore (Unix.system (Filename.quote_command "cat" [ "hello.lp" ]))
   | Unix.WEXITED n ->
       Format.eprintf "Command exited with code %d@." n;
       exit 1
diff --git a/proofs/psnj_toolbox/pipe_tests/multiproofs/dune b/proofs/psnj_toolbox/pipe_tests/multiproofs/dune
index f8b2749ab9f5d619dec376a04d660c54277fd7c0..3d197662d8bb3132b98f103210e02da6f48e8d02 100644
--- a/proofs/psnj_toolbox/pipe_tests/multiproofs/dune
+++ b/proofs/psnj_toolbox/pipe_tests/multiproofs/dune
@@ -7,4 +7,5 @@
   (glob_files encoding/*)
   (glob_files spec/main.lp))
  (libraries unix)
- (action (run ./mp.exe %{bin:psnj})))
+ (action
+  (run ./mp.exe %{bin:psnj})))