diff --git a/.cspell.json b/.cspell.json
index 556432d69a4..a2856029c2c 100644
--- a/.cspell.json
+++ b/.cspell.json
@@ -22,7 +22,7 @@
         "src/intrinsic/llvm.rs"
     ],
     "ignoreRegExpList": [
-        "/(FIXME|NOTE|TODO)\\([^)]+\\)/",
+        "/(FIXME|NOTE)\\([^)]+\\)/",
         "__builtin_\\w*"
     ]
 }
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 840c09409bb..77c1b997df5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -88,6 +88,9 @@ jobs:
     - name: Check formatting
       run: ./y.sh fmt --check
 
+    - name: Check todo
+      run: ./y.sh check-todo
+
     - name: clippy
       run: |
         cargo clippy --all-targets -- -D warnings
diff --git a/build_system/src/main.rs b/build_system/src/main.rs
index ae975c94fff..150239cbbb4 100644
--- a/build_system/src/main.rs
+++ b/build_system/src/main.rs
@@ -12,6 +12,7 @@ mod prepare;
 mod rust_tools;
 mod rustc_info;
 mod test;
+mod todo;
 mod utils;
 const BUILD_DIR: &str = "build";
 
@@ -45,7 +46,8 @@ Commands:
         clone-gcc : Clones the GCC compiler from a specified source.
         fmt       : Runs rustfmt
         fuzz      : Fuzzes `cg_gcc` using rustlantis
-        abi-test   : Runs the abi-cafe test suite on the codegen, checking for ABI compatibility with LLVM"
+        abi-test   : Runs the abi-cafe test suite on the codegen, checking for ABI compatibility with LLVM
+        check-todo : Checks todo in the project"
     );
 }
 
@@ -61,6 +63,7 @@ pub enum Command {
     Fmt,
     Fuzz,
     AbiTest,
+    CheckTodo,
 }
 
 fn main() {
@@ -80,6 +83,7 @@ fn main() {
         Some("info") => Command::Info,
         Some("clone-gcc") => Command::CloneGcc,
         Some("abi-test") => Command::AbiTest,
+        Some("check-todo") => Command::CheckTodo,
         Some("fmt") => Command::Fmt,
         Some("fuzz") => Command::Fuzz,
         Some("--help") => {
@@ -106,6 +110,7 @@ fn main() {
         Command::Fmt => fmt::run(),
         Command::Fuzz => fuzz::run(),
         Command::AbiTest => abi_test::run(),
+        Command::CheckTodo => todo::run(),
     } {
         eprintln!("Command failed to run: {e}");
         process::exit(1);
diff --git a/build_system/src/todo.rs b/build_system/src/todo.rs
new file mode 100644
index 00000000000..74b5c9ea478
--- /dev/null
+++ b/build_system/src/todo.rs
@@ -0,0 +1,87 @@
+use std::ffi::OsStr;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+const EXTENSIONS: &[&str] =
+    &["rs", "py", "js", "sh", "c", "cpp", "h", "md", "css", "ftl", "toml", "yml", "yaml"];
+const SKIP_FILES: &[&str] = &["build_system/src/todo.rs", ".github/workflows/ci.yml"];
+
+fn has_supported_extension(path: &Path) -> bool {
+    path.extension().is_some_and(|ext| EXTENSIONS.iter().any(|e| ext == OsStr::new(e)))
+}
+
+fn is_editor_temp(path: &Path) -> bool {
+    path.file_name().is_some_and(|name| name.to_string_lossy().starts_with(".#"))
+}
+
+fn list_tracked_files() -> Result<Vec<PathBuf>, String> {
+    let output = Command::new("git")
+        .args(["ls-files", "-z"])
+        .output()
+        .map_err(|e| format!("Failed to run `git ls-files`: {e}"))?;
+
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        return Err(format!("`git ls-files` failed: {stderr}"));
+    }
+
+    let mut files = Vec::new();
+    for entry in output.stdout.split(|b| *b == 0) {
+        if entry.is_empty() {
+            continue;
+        }
+        let path = std::str::from_utf8(entry)
+            .map_err(|_| "Non-utf8 path returned by `git ls-files`".to_string())?;
+        files.push(PathBuf::from(path));
+    }
+
+    Ok(files)
+}
+
+pub(crate) fn run() -> Result<(), String> {
+    let files = list_tracked_files()?;
+    let mut errors = Vec::new();
+    // Avoid embedding the task marker in source so greps only find real occurrences.
+    let todo_marker = "todo".to_ascii_uppercase();
+
+    for file in files {
+        if is_editor_temp(&file) {
+            continue;
+        }
+        if SKIP_FILES.iter().any(|skip| file.ends_with(Path::new(skip))) {
+            continue;
+        }
+        if !has_supported_extension(&file) {
+            continue;
+        }
+
+        let bytes =
+            fs::read(&file).map_err(|e| format!("Failed to read `{}`: {e}", file.display()))?;
+        let Ok(contents) = std::str::from_utf8(&bytes) else {
+            continue;
+        };
+
+        for (i, line) in contents.split('\n').enumerate() {
+            let trimmed = line.trim();
+            if trimmed.contains(&todo_marker) {
+                errors.push(format!(
+                    "{}:{}: {} is used for tasks that should be done before merging a PR; if you want to leave a message in the codebase use FIXME",
+                    file.display(),
+                    i + 1,
+                    todo_marker
+                ));
+            }
+        }
+    }
+
+    if errors.is_empty() {
+        return Ok(());
+    }
+
+    for err in &errors {
+        eprintln!("{err}");
+    }
+
+    Err(format!("found {} {}(s)", errors.len(), todo_marker))
+}