diff --git a/apheleia-formatters.el b/apheleia-formatters.el
index abdb009..606e3e2 100644
--- a/apheleia-formatters.el
+++ b/apheleia-formatters.el
@@ -89,7 +89,8 @@
     (lisp-indent . apheleia-indent-lisp-buffer)
     (ktlint . ("ktlint" "--log-level=none" "--stdin" "-F" "-"))
     (latexindent . ("latexindent" "--logfile=/dev/null"))
-    (mix-format . ("apheleia-mix" "format" "-"))
+    (mix-format . ("apheleia-from-project-root"
+                   ".formatter.exs" "mix" "format" "-"))
     (nixfmt . ("nixfmt"))
     (ocamlformat . ("ocamlformat" "-" "--name" filepath
                     "--enable-outside-detected-project"))
@@ -159,6 +160,8 @@
                 "--stderr" "--format" "quiet" "--fail-level" "fatal"))
     (ruby-standard . ("standardrb" "--stdin" filepath "--fix" "--stderr"
                       "--format" "quiet" "--fail-level" "fatal"))
+    (ruby-syntax-tree . ("apheleia-from-project-root"
+                         ".streerc" "stree" "format" filepath))
     (ruff . ("ruff" "format"
              "--silent"
              (apheleia-formatters-fill-column "--line-length")
diff --git a/apheleia-utils.el b/apheleia-utils.el
index 7e3820f..842da81 100644
--- a/apheleia-utils.el
+++ b/apheleia-utils.el
@@ -92,6 +92,17 @@ FILE-NAME."
   (when-let ((file (locate-dominating-file default-directory file-name)))
     (list file-flag (concat (expand-file-name file) file-name))))
 
+(defun apheleia-formatters-args-from-file (file-name)
+  "Extract arguments from a text file.
+Look for a file up recursively from the current directory until FILE-NAME is
+found. If found, read the file and return an Alist of lines in the file."
+  (when-let ((file (locate-dominating-file default-directory file-name)))
+    (with-temp-buffer
+      (insert-file-contents (concat (expand-file-name file) file-name))
+      (cl-loop for line in (split-string (buffer-string) "\n" t)
+               collect line)))
+  )
+
 (defun apheleia-formatters-extension-p (&rest exts)
   "Assert whether current buffer has an extension in EXTS."
   (when-let ((name buffer-file-name)
diff --git a/scripts/formatters/apheleia-from-project-root b/scripts/formatters/apheleia-from-project-root
new file mode 100755
index 0000000..1c22bed
--- /dev/null
+++ b/scripts/formatters/apheleia-from-project-root
@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+
+# USAGE: apheleia-from-project-root ROOT-FNAME CMD...
+#
+# If there is a file called ROOT-FNAME in the current directory or any
+# parent directory up to the root of the filesystem, first change to
+# that directory. If not, no worries, proceed without error. Then
+# execute CMD with provided args.
+#
+# This can be used to make sure that a formatter is executed in the
+# root directory of a project, if the file is within a project. For
+# example, ROOT-FNAME could be ".git" or ".formatter.exs" or
+# "package.json" or "pyproject.toml".
+
+if (( "$#" <= 1 )); then
+    echo >&2 "usage: apheleia-from-project-root ROOT-FNAME CMD..."
+    exit 1
+fi
+
+# This function prints the name of the current directory if it
+# contains a file or directory named after the first argument, or the
+# parent directory if it contains such a file, or the parent's parent,
+# and so on. If no such file is found it returns nonzero.
+# https://unix.stackexchange.com/a/22215
+find_upwards() {
+    fname="$1"
+
+    path="${PWD}"
+    while [[ -n "${path}" && ! -e "${path}/${fname}" ]]; do
+        path="${path%/*}"
+    done
+    [[ -n "${path}" ]] && echo "${path}"
+}
+
+if dir="$(find_upwards "$1")"; then
+    cd -- "${dir}" || exit
+fi
+
+shift
+exec "$@"
diff --git a/scripts/formatters/apheleia-mix b/scripts/formatters/apheleia-mix
deleted file mode 100755
index d2038e1..0000000
--- a/scripts/formatters/apheleia-mix
+++ /dev/null
@@ -1,22 +0,0 @@
-#!/usr/bin/env bash
-
-# This function prints the name of the current directory if it
-# contains a file or directory named after the first argument, or the
-# parent directory if it contains such a file, or the parent's parent,
-# and so on. If no such file is found it returns nonzero.
-# https://unix.stackexchange.com/a/22215
-find_upwards() {
-    fname="$1"
-
-    path="${PWD}"
-    while [[ -n "${path}" && ! -e "${path}/${fname}" ]]; do
-        path="${path%/*}"
-    done
-    [[ -n "${path}" ]] && echo "${path}"
-}
-
-if dir="$(find_upwards .formatter.exs)"; then
-    cd -- "${dir}" || exit
-fi
-
-exec mix "$@"
diff --git a/test/formatters/installers/ruby-syntax-tree.bash b/test/formatters/installers/ruby-syntax-tree.bash
new file mode 100644
index 0000000..9468c07
--- /dev/null
+++ b/test/formatters/installers/ruby-syntax-tree.bash
@@ -0,0 +1,4 @@
+# Need ruby for gem
+apt-get install -y ruby
+
+gem install syntax_tree
diff --git a/test/formatters/samplecode/ruby-syntax-tree/in.rb b/test/formatters/samplecode/ruby-syntax-tree/in.rb
new file mode 100644
index 0000000..2a2f35a
--- /dev/null
+++ b/test/formatters/samplecode/ruby-syntax-tree/in.rb
@@ -0,0 +1,13 @@
+        d=[30644250780,9003106878,
+    30636278846,66641217692,4501790980,
+ 671_24_603036,131_61973916,66_606629_920,
+   30642677916,30643069058];a,s=[],$*[0]
+      s.each_byte{|b|a<<("%036b"%d[b.
+         chr.to_i]).scan(/\d{6}/)}
+          a.transpose.each{ |a|
+            a.join.each_byte{\
+             |i|print i==49?\
+               ($*[1]||"#")\
+                 :32.chr}
+                   puts
+                    }
diff --git a/test/formatters/samplecode/ruby-syntax-tree/out.rb b/test/formatters/samplecode/ruby-syntax-tree/out.rb
new file mode 100644
index 0000000..3bf1506
--- /dev/null
+++ b/test/formatters/samplecode/ruby-syntax-tree/out.rb
@@ -0,0 +1,18 @@
+d = [
+  30_644_250_780,
+  9_003_106_878,
+  30_636_278_846,
+  66_641_217_692,
+  4_501_790_980,
+  671_24_603036,
+  131_61973916,
+  66_606629_920,
+  30_642_677_916,
+  30_643_069_058
+]
+a, s = [], $*[0]
+s.each_byte { |b| a << ("%036b" % d[b.chr.to_i]).scan(/\d{6}/) }
+a.transpose.each do |a|
+  a.join.each_byte { |i| print i == 49 ? ($*[1] || "#") : 32.chr }
+  puts
+end