diff --git a/Cargo.lock b/Cargo.lock
index 6eaaa86..ac05bd2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "addr2line"
@@ -364,6 +364,12 @@ dependencies = [
  "powerfmt",
 ]
 
+[[package]]
+name = "diff"
+version = "0.1.13"
+source = "registry+/~https://github.com/rust-lang/crates.io-index"
+checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
+
 [[package]]
 name = "either"
 version = "1.13.0"
@@ -1072,6 +1078,16 @@ dependencies = [
  "zerocopy",
 ]
 
+[[package]]
+name = "pretty_assertions"
+version = "1.4.1"
+source = "registry+/~https://github.com/rust-lang/crates.io-index"
+checksum = "3ae130e2f271fbc2ac3a40fb1d07180839cdbbe443c7a27e1e3c13c5cac0116d"
+dependencies = [
+ "diff",
+ "yansi",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.89"
@@ -1483,6 +1499,7 @@ dependencies = [
  "indicatif",
  "nonempty",
  "pest",
+ "pretty_assertions",
  "tokio",
  "tracing",
  "tracing-log",
@@ -2344,6 +2361,12 @@ version = "0.52.6"
 source = "registry+/~https://github.com/rust-lang/crates.io-index"
 checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
 
+[[package]]
+name = "yansi"
+version = "1.0.1"
+source = "registry+/~https://github.com/rust-lang/crates.io-index"
+checksum = "cfe53a6657fd280eaa890a3bc59152892ffa3e30101319d168b781ed6529b049"
+
 [[package]]
 name = "zerocopy"
 version = "0.7.35"
diff --git a/Cargo.toml b/Cargo.toml
index 2cc7129..bcfc3bb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,3 +27,4 @@ tokio = { version = "1.41.0", features = ["full"] }
 tracing-log = "0.2.0"
 indicatif = "0.17.8"
 clap-verbosity-flag = "2.2.2"
+pretty_assertions = "1.4.1"
diff --git a/src/commands/format.rs b/src/commands/format.rs
index d79f11e..68c59ac 100644
--- a/src/commands/format.rs
+++ b/src/commands/format.rs
@@ -15,6 +15,7 @@ use clap::Parser;
 use codespan_reporting::files::SimpleFile;
 use codespan_reporting::term::emit;
 use colored::Colorize;
+use pretty_assertions::StrComparison;
 use walkdir::WalkDir;
 use wdl::ast::Document;
 use wdl::ast::Node;
@@ -70,8 +71,12 @@ pub struct FormatArgs {
     pub indentation_size: Option<usize>,
 
     /// Overwrite the WDL documents with the formatted versions
-    #[arg(long)]
+    #[arg(long, conflicts_with = "check")]
     pub overwrite: bool,
+
+    /// Check if files are formatted correctly and print diff if not
+    #[arg(long, conflicts_with = "overwrite")]
+    pub check: bool,
 }
 
 /// Reads source from the given path.
@@ -103,14 +108,16 @@ fn format_document(
     overwrite: bool,
     report_mode: Mode,
     no_color: bool,
+    check: bool,
 ) -> Result<usize> {
     if path.to_str() != Some("-") {
+        let action = if check { "checking" } else { "formatting" };
         println!(
-            "{formatting} `{path}`",
-            formatting = if no_color {
-                "formatting".normal()
+            "{action_colored} `{path}`",
+            action_colored = if no_color {
+                action.normal()
             } else {
-                "formatting".green()
+                action.green()
             },
             path = path.display()
         );
@@ -140,6 +147,15 @@ fn format_document(
     let formatter = Formatter::new(config);
     let formatted = formatter.format(&document)?;
 
+    if check {
+        if formatted != source {
+            print!("{}", StrComparison::new(&source, &formatted));
+            return Ok(1);
+        }
+        println!("`{path}` is formatted correctly", path = path.display());
+        return Ok(0);
+    }
+
     if overwrite {
         fs::write(path, formatted)
             .with_context(|| format!("failed to write `{path}`", path = path.display()))?;
@@ -172,8 +188,8 @@ pub fn format(args: FormatArgs) -> Result<()> {
 
     let mut diagnostics = 0;
     if args.path.to_str() != Some("-") && args.path.is_dir() {
-        if !args.overwrite {
-            bail!("formatting a directory requires the `--overwrite` option");
+        if !args.overwrite && !args.check {
+            bail!("formatting a directory requires the `--overwrite` or `--check` option");
         }
 
         for entry in WalkDir::new(&args.path) {
@@ -194,6 +210,7 @@ pub fn format(args: FormatArgs) -> Result<()> {
                 args.overwrite,
                 args.report_mode,
                 args.no_color,
+                args.check,
             )?;
         }
     } else {
@@ -203,6 +220,7 @@ pub fn format(args: FormatArgs) -> Result<()> {
             args.overwrite,
             args.report_mode,
             args.no_color,
+            args.check,
         )?;
     }