diff --git a/Cargo.lock b/Cargo.lock
index 27f7a71..696db77 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -291,6 +291,12 @@ version = "2.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "524cbf6897b527295dff137cec09ecf3a05f4fddffd7dfcd1585403449e74198"
 
+[[package]]
+name = "difflib"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
+
 [[package]]
 name = "doc-comment"
 version = "0.3.3"
@@ -1078,6 +1084,7 @@ dependencies = [
  "bstr",
  "clap",
  "clap-verbosity-flag",
+ "difflib",
  "env_logger 0.8.1",
  "ignore",
  "log",
diff --git a/Cargo.toml b/Cargo.toml
index 0ffd1af..f87e14c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -47,6 +47,7 @@ log = "0.4"
 env_logger = "0.8"
 bstr = "0.2"
 ahash = "0.5.8"
+difflib = "0.4"
 
 [dev-dependencies]
 assert_fs = "1.0"
diff --git a/crates/typos/src/checks.rs b/crates/typos/src/checks.rs
index 56a689d..922fc9d 100644
--- a/crates/typos/src/checks.rs
+++ b/crates/typos/src/checks.rs
@@ -94,7 +94,7 @@ struct ReportContext<'m, 'r> {
 
 impl<'m, 'r> report::Report for ReportContext<'m, 'r> {
     fn report(&self, msg: report::Message) -> bool {
-        let msg = msg.context(self.context.clone());
+        let msg = msg.context(Some(self.context.clone()));
         self.reporter.report(msg)
     }
 }
@@ -188,7 +188,7 @@ impl Check for Typos {
                 Some(corrections) => {
                     let byte_offset = ident.offset();
                     let msg = report::Typo {
-                        context: report::Context::None,
+                        context: None,
                         buffer: std::borrow::Cow::Borrowed(buffer.as_bytes()),
                         byte_offset,
                         typo: ident.token(),
@@ -203,7 +203,7 @@ impl Check for Typos {
                             Some(corrections) => {
                                 let byte_offset = word.offset();
                                 let msg = report::Typo {
-                                    context: report::Context::None,
+                                    context: None,
                                     buffer: std::borrow::Cow::Borrowed(buffer.as_bytes()),
                                     byte_offset,
                                     typo: word.token(),
@@ -236,7 +236,7 @@ impl Check for Typos {
                 Some(corrections) => {
                     let byte_offset = ident.offset();
                     let msg = report::Typo {
-                        context: report::Context::None,
+                        context: None,
                         buffer: std::borrow::Cow::Borrowed(buffer),
                         byte_offset,
                         typo: ident.token(),
@@ -251,7 +251,7 @@ impl Check for Typos {
                             Some(corrections) => {
                                 let byte_offset = word.offset();
                                 let msg = report::Typo {
-                                    context: report::Context::None,
+                                    context: None,
                                     buffer: std::borrow::Cow::Borrowed(buffer),
                                     byte_offset,
                                     typo: word.token(),
@@ -300,7 +300,7 @@ impl Check for ParseIdentifiers {
         let typos_found = false;
 
         let msg = report::Parse {
-            context: report::Context::None,
+            context: None,
             kind: report::ParseKind::Identifier,
             data: parser.parse_str(buffer).map(|i| i.token()).collect(),
         };
@@ -321,7 +321,7 @@ impl Check for ParseIdentifiers {
         let typos_found = false;
 
         let msg = report::Parse {
-            context: report::Context::None,
+            context: None,
             kind: report::ParseKind::Identifier,
             data: parser.parse_bytes(buffer).map(|i| i.token()).collect(),
         };
@@ -363,7 +363,7 @@ impl Check for ParseWords {
         let typos_found = false;
 
         let msg = report::Parse {
-            context: report::Context::None,
+            context: None,
             kind: report::ParseKind::Word,
             data: parser
                 .parse_str(buffer)
@@ -387,7 +387,7 @@ impl Check for ParseWords {
         let typos_found = false;
 
         let msg = report::Parse {
-            context: report::Context::None,
+            context: None,
             kind: report::ParseKind::Word,
             data: parser
                 .parse_bytes(buffer)
diff --git a/crates/typos/src/report.rs b/crates/typos/src/report.rs
index a1386ca..bd45753 100644
--- a/crates/typos/src/report.rs
+++ b/crates/typos/src/report.rs
@@ -39,7 +39,7 @@ impl<'m> Message<'m> {
         }
     }
 
-    pub fn context(self, context: Context<'m>) -> Self {
+    pub fn context(self, context: Option<Context<'m>>) -> Self {
         match self {
             Message::Typo(typo) => {
                 let typo = typo.context(context);
@@ -65,7 +65,7 @@ pub struct BinaryFile<'m> {
 #[non_exhaustive]
 pub struct Typo<'m> {
     #[serde(flatten)]
-    pub context: Context<'m>,
+    pub context: Option<Context<'m>>,
     #[serde(skip)]
     pub buffer: Cow<'m, [u8]>,
     pub byte_offset: usize,
@@ -76,7 +76,7 @@ pub struct Typo<'m> {
 impl<'m> Default for Typo<'m> {
     fn default() -> Self {
         Self {
-            context: Context::None,
+            context: None,
             buffer: Cow::Borrowed(&[]),
             byte_offset: 0,
             typo: "",
@@ -91,13 +91,6 @@ impl<'m> Default for Typo<'m> {
 pub enum Context<'m> {
     File(FileContext<'m>),
     Path(PathContext<'m>),
-    None,
-}
-
-impl<'m> Default for Context<'m> {
-    fn default() -> Self {
-        Context::None
-    }
 }
 
 impl<'m> std::fmt::Display for Context<'m> {
@@ -105,7 +98,6 @@ impl<'m> std::fmt::Display for Context<'m> {
         match self {
             Context::File(c) => write!(f, "{}:{}", c.path.display(), c.line_num),
             Context::Path(c) => write!(f, "{}", c.path.display()),
-            Context::None => Ok(()),
         }
     }
 }
@@ -172,7 +164,7 @@ impl<'m> Default for File<'m> {
 #[non_exhaustive]
 pub struct Parse<'m> {
     #[serde(flatten)]
-    pub context: Context<'m>,
+    pub context: Option<Context<'m>>,
     pub kind: ParseKind,
     pub data: Vec<&'m str>,
 }
@@ -180,7 +172,7 @@ pub struct Parse<'m> {
 impl<'m> Default for Parse<'m> {
     fn default() -> Self {
         Self {
-            context: Context::None,
+            context: None,
             kind: ParseKind::Identifier,
             data: vec![],
         }
@@ -294,13 +286,15 @@ fn print_brief_correction(msg: &Typo) {
         crate::Status::Invalid => {
             println!(
                 "{}:{}: {} is disallowed",
-                msg.context, msg.byte_offset, msg.typo,
+                context_display(&msg.context),
+                msg.byte_offset,
+                msg.typo,
             );
         }
         crate::Status::Corrections(corrections) => {
             println!(
                 "{}:{}: {} -> {}",
-                msg.context,
+                context_display(&msg.context),
                 msg.byte_offset,
                 msg.typo,
                 itertools::join(corrections.iter(), ", ")
@@ -318,7 +312,9 @@ fn print_long_correction(msg: &Typo) {
             writeln!(
                 handle,
                 "{}:{}: {} is disallowed",
-                msg.context, msg.byte_offset, msg.typo,
+                context_display(&msg.context),
+                msg.byte_offset,
+                msg.typo,
             )
             .unwrap();
         }
@@ -332,9 +328,15 @@ fn print_long_correction(msg: &Typo) {
             .unwrap();
         }
     }
-    writeln!(handle, "  --> {}:{}", msg.context, msg.byte_offset).unwrap();
+    writeln!(
+        handle,
+        "  --> {}:{}",
+        context_display(&msg.context),
+        msg.byte_offset
+    )
+    .unwrap();
 
-    if let Context::File(context) = &msg.context {
+    if let Some(Context::File(context)) = &msg.context {
         let line_num = context.line_num.to_string();
         let line_indent: String = itertools::repeat_n(" ", line_num.len()).collect();
 
@@ -350,6 +352,13 @@ fn print_long_correction(msg: &Typo) {
     }
 }
 
+fn context_display<'c>(context: &'c Option<Context<'c>>) -> &'c dyn std::fmt::Display {
+    context
+        .as_ref()
+        .map(|c| c as &dyn std::fmt::Display)
+        .unwrap_or(&"")
+}
+
 #[derive(Copy, Clone, Debug)]
 pub struct PrintJson;
 
diff --git a/src/args.rs b/src/args.rs
index 2bab458..f9d2b0f 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -54,6 +54,10 @@ pub(crate) struct Args {
     /// Ignore implicit configuration files.
     pub(crate) isolated: bool,
 
+    #[structopt(long)]
+    /// Print a diff of what would change
+    pub(crate) diff: bool,
+
     #[structopt(long, short = "w")]
     /// Write corrections out
     pub(crate) write_changes: bool,
diff --git a/src/dict.rs b/src/dict.rs
index d0e0aa9..ab602d6 100644
--- a/src/dict.rs
+++ b/src/dict.rs
@@ -29,6 +29,10 @@ impl BuiltIn {
         &'s self,
         word_token: typos::tokens::Word<'w>,
     ) -> Option<Status<'s>> {
+        if word_token.case() == typos::tokens::Case::None {
+            return None;
+        }
+
         let word = word_token.token();
         let mut corrections = if let Some(correction) = self.correct_with_dict(word) {
             self.correct_with_vars(word)
@@ -211,17 +215,19 @@ impl<'i, 'w, D: typos::Dictionary> typos::Dictionary for Override<'i, 'w, D> {
     }
 
     fn correct_word<'s, 't>(&'s self, word: typos::tokens::Word<'t>) -> Option<Status<'s>> {
+        if word.case() == typos::tokens::Case::None {
+            return None;
+        }
+
         // Skip hashing if we can
-        if !self.words.is_empty() {
+        let custom = if !self.words.is_empty() {
             let w = UniCase::new(word.token());
             // HACK: couldn't figure out the lifetime issue with replacing `cloned` with `borrow`
-            self.words
-                .get(&w)
-                .cloned()
-                .or_else(|| self.inner.correct_word(word))
+            self.words.get(&w).cloned()
         } else {
             None
-        }
+        };
+        custom.or_else(|| self.inner.correct_word(word))
     }
 }
 
diff --git a/src/diff.rs b/src/diff.rs
new file mode 100644
index 0000000..a49ae13
--- /dev/null
+++ b/src/diff.rs
@@ -0,0 +1,93 @@
+use std::collections::BTreeMap;
+use std::sync;
+
+use bstr::ByteSlice;
+
+pub struct Diff<'r> {
+    reporter: &'r dyn typos::report::Report,
+    deferred: sync::Mutex<crate::replace::Deferred>,
+}
+
+impl<'r> Diff<'r> {
+    pub(crate) fn new(reporter: &'r dyn typos::report::Report) -> Self {
+        Self {
+            reporter,
+            deferred: sync::Mutex::new(crate::replace::Deferred::default()),
+        }
+    }
+
+    pub fn show(&self) -> Result<(), std::io::Error> {
+        let deferred = self.deferred.lock().unwrap();
+
+        for (path, corrections) in deferred.content.iter() {
+            let buffer = std::fs::read(path)?;
+
+            let mut original = Vec::new();
+            let mut corrected = Vec::new();
+            for (line_idx, line) in buffer.lines_with_terminator().enumerate() {
+                original.push(String::from_utf8_lossy(line).into_owned());
+
+                let line_num = line_idx + 1;
+                let line = if let Some(corrections) = corrections.get(&line_num) {
+                    let line = line.to_vec();
+                    crate::replace::correct(line, &corrections)
+                } else {
+                    line.to_owned()
+                };
+                corrected.push(String::from_utf8_lossy(&line).into_owned())
+            }
+
+            let display_path = path.display().to_string();
+            let diff = difflib::unified_diff(
+                &original,
+                &corrected,
+                display_path.as_str(),
+                display_path.as_str(),
+                "original",
+                "corrected",
+                0,
+            );
+            for line in diff {
+                print!("{}", line);
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl<'r> typos::report::Report for Diff<'r> {
+    fn report(&self, msg: typos::report::Message<'_>) -> bool {
+        let typo = match &msg {
+            typos::report::Message::Typo(typo) => typo,
+            _ => return self.reporter.report(msg),
+        };
+
+        let corrections = match &typo.corrections {
+            typos::Status::Corrections(corrections) if corrections.len() == 1 => corrections,
+            _ => return self.reporter.report(msg),
+        };
+
+        match &typo.context {
+            Some(typos::report::Context::File(file)) => {
+                let path = file.path.to_owned();
+                let line_num = file.line_num;
+                let correction = crate::replace::Correction::new(
+                    typo.byte_offset,
+                    typo.typo,
+                    corrections[0].as_ref(),
+                );
+                let mut deferred = self.deferred.lock().unwrap();
+                let content = deferred
+                    .content
+                    .entry(path)
+                    .or_insert_with(BTreeMap::new)
+                    .entry(line_num)
+                    .or_insert_with(Vec::new);
+                content.push(correction);
+                false
+            }
+            _ => msg.is_correction(),
+        }
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 5206c26..00ce2e5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,6 +10,7 @@ mod args;
 mod checks;
 mod config;
 mod dict;
+mod diff;
 mod replace;
 
 fn main() {
@@ -86,7 +87,10 @@ fn run() -> Result<i32, anyhow::Error> {
 
         let mut reporter = args.format.reporter();
         let replace_reporter = replace::Replace::new(reporter);
-        if args.write_changes {
+        let diff_reporter = diff::Diff::new(reporter);
+        if args.diff {
+            reporter = &diff_reporter;
+        } else if args.write_changes {
             reporter = &replace_reporter;
         }
 
@@ -129,7 +133,9 @@ fn run() -> Result<i32, anyhow::Error> {
             errors_found = true;
         }
 
-        if args.write_changes {
+        if args.diff {
+            diff_reporter.show()?;
+        } else if args.write_changes {
             replace_reporter.write()?;
         }
     }
diff --git a/src/replace.rs b/src/replace.rs
index 22a6376..aef418a 100644
--- a/src/replace.rs
+++ b/src/replace.rs
@@ -67,7 +67,7 @@ impl<'r> typos::report::Report for Replace<'r> {
         };
 
         match &typo.context {
-            typos::report::Context::File(file) => {
+            Some(typos::report::Context::File(file)) => {
                 let path = file.path.to_owned();
                 let line_num = file.line_num;
                 let correction =
@@ -82,7 +82,7 @@ impl<'r> typos::report::Report for Replace<'r> {
                 content.push(correction);
                 false
             }
-            typos::report::Context::Path(path) => {
+            Some(typos::report::Context::Path(path)) => {
                 let path = path.path.to_owned();
                 let correction =
                     Correction::new(typo.byte_offset, typo.typo, corrections[0].as_ref());
@@ -97,20 +97,20 @@ impl<'r> typos::report::Report for Replace<'r> {
 }
 
 #[derive(Clone, Debug, Default)]
-struct Deferred {
-    content: BTreeMap<path::PathBuf, BTreeMap<usize, Vec<Correction>>>,
-    paths: BTreeMap<path::PathBuf, Vec<Correction>>,
+pub(crate) struct Deferred {
+    pub(crate) content: BTreeMap<path::PathBuf, BTreeMap<usize, Vec<Correction>>>,
+    pub(crate) paths: BTreeMap<path::PathBuf, Vec<Correction>>,
 }
 
 #[derive(Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
-struct Correction {
+pub(crate) struct Correction {
     pub byte_offset: usize,
     pub typo: Vec<u8>,
     pub correction: Vec<u8>,
 }
 
 impl Correction {
-    fn new(byte_offset: usize, typo: &str, correction: &str) -> Self {
+    pub(crate) fn new(byte_offset: usize, typo: &str, correction: &str) -> Self {
         Self {
             byte_offset,
             typo: typo.as_bytes().to_vec(),
@@ -119,7 +119,7 @@ impl Correction {
     }
 }
 
-fn correct(mut line: Vec<u8>, corrections: &[Correction]) -> Vec<u8> {
+pub(crate) fn correct(mut line: Vec<u8>, corrections: &[Correction]) -> Vec<u8> {
     let mut corrections: Vec<_> = corrections.iter().collect();
     corrections.sort_unstable();
     corrections.reverse();
@@ -209,12 +209,12 @@ mod test {
         let replace = Replace::new(&primary);
         replace.report(
             typos::report::Typo::default()
-                .context(
+                .context(Some(
                     typos::report::FileContext::default()
                         .path(input_file.path())
                         .line_num(1)
                         .into(),
-                )
+                ))
                 .buffer(std::borrow::Cow::Borrowed(b"1 foo 2\n3 4 5"))
                 .byte_offset(2)
                 .typo("foo")
@@ -238,11 +238,11 @@ mod test {
         let replace = Replace::new(&primary);
         replace.report(
             typos::report::Typo::default()
-                .context(
+                .context(Some(
                     typos::report::PathContext::default()
                         .path(input_file.path())
                         .into(),
-                )
+                ))
                 .buffer(std::borrow::Cow::Borrowed(b"foo.txt"))
                 .byte_offset(0)
                 .typo("foo")