diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d747113..313b530 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -18,3 +18,5 @@ jobs:
       env:
         SPEC_DENY_WARNINGS: 1
       run: mdbook build
+    - name: Run style check
+      run: (cd style-check && cargo run -- ../spec)
diff --git a/docs/authoring.md b/docs/authoring.md
index 942ceee..6d7e892 100644
--- a/docs/authoring.md
+++ b/docs/authoring.md
@@ -2,7 +2,21 @@
 
 ## Markdown formatting
 
-* Use ATX-style heading with sentence case.
+* Use [ATX-style headings][atx] (not Setext) with [sentence case].
+* Do not use tabs, only spaces.
+* Files must end with a newline.
+* Lines must not end with spaces. Double spaces have semantic meaning, but can be invisible. Use a trailing backslash if you need a hard line break.
+* If possible, avoid double blank lines.
+* Do not use indented code blocks, use 3+ backticks code blocks instead.
+* Code blocks should have an explicit language tag.
+* Do not wrap long lines. This helps with reviewing diffs of the source.
+* Use [smart punctuation] instead of Unicode characters. For example, use `---` for em-dash instead of the Unicode character. Characters like em-dash can be difficult to see in a fixed-width editor, and some editors may not have easy methods to enter such characters.
+
+There are automated checks for some of these rules. Run `cargo run --manifest-path style-check/Cargo.toml -- spec` to run them locally.
+
+[atx]: https://spec.commonmark.org/0.31.2/#atx-headings
+[sentence case]: https://apastyle.apa.org/style-grammar-guidelines/capitalization/sentence-case
+[smart punctuation]: https://rust-lang.github.io/mdBook/format/markdown.html#smart-punctuation
 
 ## Special markdown constructs
 
diff --git a/style-check/.gitignore b/style-check/.gitignore
new file mode 100644
index 0000000..eb5a316
--- /dev/null
+++ b/style-check/.gitignore
@@ -0,0 +1 @@
+target
diff --git a/style-check/Cargo.lock b/style-check/Cargo.lock
new file mode 100644
index 0000000..11511a8
--- /dev/null
+++ b/style-check/Cargo.lock
@@ -0,0 +1,71 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "bitflags"
+version = "2.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed570934406eb16438a4e976b1b4500774099c13b8cb96eec99f620f05090ddf"
+
+[[package]]
+name = "getopts"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14dbbfd5c71d70241ecf9e6f13737f7b5ce823821063188d7e46c41d371eebd5"
+dependencies = [
+ "unicode-width",
+]
+
+[[package]]
+name = "memchr"
+version = "2.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "523dc4f511e55ab87b694dc30d0f820d60906ef06413f93d4d7a1385599cc149"
+
+[[package]]
+name = "pulldown-cmark"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dce76ce678ffc8e5675b22aa1405de0b7037e2fdf8913fea40d1926c6fe1e6e7"
+dependencies = [
+ "bitflags",
+ "getopts",
+ "memchr",
+ "pulldown-cmark-escape",
+ "unicase",
+]
+
+[[package]]
+name = "pulldown-cmark-escape"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d5d8f9aa0e3cbcfaf8bf00300004ee3b72f74770f9cbac93f6928771f613276b"
+
+[[package]]
+name = "style-check"
+version = "0.1.0"
+dependencies = [
+ "pulldown-cmark",
+]
+
+[[package]]
+name = "unicase"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7d2d4dafb69621809a81864c9c1b864479e1235c0dd4e199924b9742439ed89"
+dependencies = [
+ "version_check",
+]
+
+[[package]]
+name = "unicode-width"
+version = "0.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e51733f11c9c4f72aa0c160008246859e340b00807569a0da0e7a1079b27ba85"
+
+[[package]]
+name = "version_check"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
diff --git a/style-check/Cargo.toml b/style-check/Cargo.toml
new file mode 100644
index 0000000..083aeca
--- /dev/null
+++ b/style-check/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "style-check"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+pulldown-cmark = "0.10.0"
diff --git a/style-check/src/main.rs b/style-check/src/main.rs
new file mode 100644
index 0000000..26f55c7
--- /dev/null
+++ b/style-check/src/main.rs
@@ -0,0 +1,137 @@
+use std::env;
+use std::error::Error;
+use std::fs;
+use std::path::Path;
+
+macro_rules! style_error {
+    ($bad:expr, $path:expr, $($arg:tt)*) => {
+        *$bad = true;
+        eprint!("error in {}: ", $path.display());
+        eprintln!("{}", format_args!($($arg)*));
+    };
+}
+
+fn main() {
+    let arg = env::args().nth(1).unwrap_or_else(|| {
+        eprintln!("Please pass a src directory as the first argument");
+        std::process::exit(1);
+    });
+
+    let mut bad = false;
+    if let Err(e) = check_directory(&Path::new(&arg), &mut bad) {
+        eprintln!("error: {}", e);
+        std::process::exit(1);
+    }
+    if bad {
+        eprintln!("some style checks failed");
+        std::process::exit(1);
+    }
+    eprintln!("passed!");
+}
+
+fn check_directory(dir: &Path, bad: &mut bool) -> Result<(), Box<dyn Error>> {
+    for entry in fs::read_dir(dir)? {
+        let entry = entry?;
+        let path = entry.path();
+
+        if path.is_dir() {
+            check_directory(&path, bad)?;
+            continue;
+        }
+
+        if !matches!(
+            path.extension().and_then(|p| p.to_str()),
+            Some("md") | Some("html")
+        ) {
+            // This may be extended in the future if other file types are needed.
+            style_error!(bad, path, "expected only md or html in src");
+        }
+
+        let contents = fs::read_to_string(&path)?;
+        if contents.contains("#![feature") {
+            style_error!(bad, path, "#![feature] attributes are not allowed");
+        }
+        if !cfg!(windows) && contents.contains('\r') {
+            style_error!(
+                bad,
+                path,
+                "CR characters not allowed, must use LF line endings"
+            );
+        }
+        if contents.contains('\t') {
+            style_error!(bad, path, "tab characters not allowed, use spaces");
+        }
+        if contents.contains('\u{2013}') {
+            style_error!(bad, path, "en-dash not allowed, use two dashes like --");
+        }
+        if contents.contains('\u{2014}') {
+            style_error!(bad, path, "em-dash not allowed, use three dashes like ---");
+        }
+        if !contents.ends_with('\n') {
+            style_error!(bad, path, "file must end with a newline");
+        }
+        for line in contents.lines() {
+            if line.ends_with(' ') {
+                style_error!(bad, path, "lines must not end with spaces");
+            }
+        }
+        cmark_check(&path, bad, &contents)?;
+    }
+    Ok(())
+}
+
+fn cmark_check(path: &Path, bad: &mut bool, contents: &str) -> Result<(), Box<dyn Error>> {
+    use pulldown_cmark::{BrokenLink, CodeBlockKind, Event, Options, Parser, Tag};
+
+    macro_rules! cmark_error {
+        ($bad:expr, $path:expr, $range:expr, $($arg:tt)*) => {
+            *$bad = true;
+            let lineno = contents[..$range.start].chars().filter(|&ch| ch == '\n').count() + 1;
+            eprint!("error in {} (line {}): ", $path.display(), lineno);
+            eprintln!("{}", format_args!($($arg)*));
+        }
+    }
+
+    let options = Options::all();
+    // Can't use `bad` because it would get captured in closure.
+    let mut link_err = false;
+    let mut cb = |link: BrokenLink<'_>| {
+        cmark_error!(
+            &mut link_err,
+            path,
+            link.span,
+            "broken {:?} link (reference `{}`)",
+            link.link_type,
+            link.reference
+        );
+        None
+    };
+    let parser = Parser::new_with_broken_link_callback(contents, options, Some(&mut cb));
+
+    for (event, range) in parser.into_offset_iter() {
+        match event {
+            Event::Start(Tag::CodeBlock(CodeBlockKind::Indented)) => {
+                cmark_error!(
+                    bad,
+                    path,
+                    range,
+                    "indented code blocks should use triple backtick-style \
+                    with a language identifier"
+                );
+            }
+            Event::Start(Tag::CodeBlock(CodeBlockKind::Fenced(languages))) => {
+                if languages.is_empty() {
+                    cmark_error!(
+                        bad,
+                        path,
+                        range,
+                        "code block should include an explicit language",
+                    );
+                }
+            }
+            _ => {}
+        }
+    }
+    *bad |= link_err;
+    Ok(())
+}