diff --git a/src/command_fmt.cc b/src/command_fmt.cc
index 820273fd..f255cd1f 100644
--- a/src/command_fmt.cc
+++ b/src/command_fmt.cc
@@ -1,23 +1,46 @@
 #include <sourcemeta/jsontoolkit/json.h>
 #include <sourcemeta/jsontoolkit/jsonschema.h>
 
-#include <cstdlib>  // EXIT_SUCCESS
+#include <cstdlib>  // EXIT_SUCCESS, EXIT_FAILURE
 #include <fstream>  // std::ofstream
 #include <iostream> // std::cerr, std::endl
+#include <sstream>  // std::ostringstream
 
 #include "command.h"
 #include "utils.h"
 
-// TODO: Support a `--check` option to do an assert like Deno does
 auto intelligence::jsonschema::cli::fmt(
     const std::span<const std::string> &arguments) -> int {
-  const auto options{parse_options(arguments, {})};
+  const auto options{parse_options(arguments, {"c", "check"})};
+
   for (const auto &entry : for_each_json(options.at(""))) {
-    log_verbose(options) << "Formatting: " << entry.first.string() << "\n";
-    std::ofstream output{entry.first};
-    sourcemeta::jsontoolkit::prettify(
-        entry.second, output, sourcemeta::jsontoolkit::schema_format_compare);
-    output << std::endl;
+    if (options.contains("c") || options.contains("check")) {
+      log_verbose(options) << "Checking: " << entry.first.string() << "\n";
+      std::ifstream input{entry.first};
+      std::ostringstream buffer;
+      buffer << input.rdbuf();
+      std::ostringstream expected;
+      sourcemeta::jsontoolkit::prettify(
+          entry.second, expected,
+          sourcemeta::jsontoolkit::schema_format_compare);
+      expected << "\n";
+
+      if (buffer.str() == expected.str()) {
+        log_verbose(options) << "PASS: " << entry.first.string() << "\n";
+      } else {
+        std::cerr << "FAIL: " << entry.first.string() << "\n";
+        std::cerr << "Got: \n"
+                  << buffer.str() << "\nBut expected:\n"
+                  << expected.str() << "\n";
+        return EXIT_FAILURE;
+      }
+    } else {
+      log_verbose(options) << "Formatting: " << entry.first.string() << "\n";
+      std::ofstream output{entry.first};
+      sourcemeta::jsontoolkit::prettify(
+          entry.second, output, sourcemeta::jsontoolkit::schema_format_compare);
+      output << std::endl;
+    }
   }
 
   return EXIT_SUCCESS;
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index b3f36683..e30acfe2 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -11,6 +11,8 @@ add_jsonschema_test_unix(format_single)
 add_jsonschema_test_unix(format_invalid_path)
 add_jsonschema_test_unix(format_directory)
 add_jsonschema_test_unix(format_cwd)
+add_jsonschema_test_unix(format_check_single_fail)
+add_jsonschema_test_unix(format_check_single_pass)
 add_jsonschema_test_unix(frame)
 add_jsonschema_test_unix(validate_pass)
 add_jsonschema_test_unix(validate_fail)
diff --git a/test/format_check_single_fail.sh b/test/format_check_single_fail.sh
new file mode 100755
index 00000000..a16733e8
--- /dev/null
+++ b/test/format_check_single_fail.sh
@@ -0,0 +1,34 @@
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+
+TMP="$(mktemp -d)"
+clean() { rm -rf "$TMP"; }
+trap clean EXIT
+
+cat << 'EOF' > "$TMP/schema.json"
+{
+  "type": 1,
+  "$schema": "http://json-schema.org/draft-04/schema#"
+}
+EOF
+
+"$1" fmt "$TMP/schema.json" --check && CODE="$?" || CODE="$?"
+
+if [ "$CODE" = "0" ]
+then
+  echo "FAIL" 1>&2
+  exit 1
+else
+  echo "PASS" 1>&2
+fi
+
+cat << 'EOF' > "$TMP/expected.json"
+{
+  "type": 1,
+  "$schema": "http://json-schema.org/draft-04/schema#"
+}
+EOF
+
+diff "$TMP/schema.json" "$TMP/expected.json"
diff --git a/test/format_check_single_pass.sh b/test/format_check_single_pass.sh
new file mode 100755
index 00000000..d0b045ba
--- /dev/null
+++ b/test/format_check_single_pass.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+
+TMP="$(mktemp -d)"
+clean() { rm -rf "$TMP"; }
+trap clean EXIT
+
+cat << 'EOF' > "$TMP/schema.json"
+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "type": 1
+}
+EOF
+
+"$1" fmt "$TMP/schema.json" --check
+
+cat << 'EOF' > "$TMP/expected.json"
+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "type": 1
+}
+EOF
+
+diff "$TMP/schema.json" "$TMP/expected.json"