diff --git a/build_tools/find_weak_odrs.py b/build_tools/find_weak_odrs.py
new file mode 100755
index 000000000..da7a45d12
--- /dev/null
+++ b/build_tools/find_weak_odrs.py
@@ -0,0 +1,63 @@
+#!/usr/bin/env python3
+
+# Finds potential ODR violations due to weak symbols.
+# For example, if you have two different structs with the same name in different files,
+# their inline constructors may collide.
+# This works only on Linux. It is designed to be run from the cmake build directory.
+# clang seems more willing to emit non-inlined ctors. Of course perform a Debug build.
+
+import re
+import subprocess
+
+output = subprocess.check_output(
+    "nm --radix=d -g --demangle -l --print-size CMakeFiles/fishlib.dir/src/*.o",
+    shell=True,
+    text=True,
+)
+files_by_name = {}  # Symbol to set of paths
+sizes_by_name = {}  # Symbol to set of int sizes
+
+for line in output.split("\n"):
+    # Keep only weak symbols with default values (e.g. emitted inline functions).
+    # Example line: "0000000000000000 0000000000000107 W symbol_name"
+    # First number is offset, second is size.
+    # Note this is decimal because of radix=d.
+    m = re.match(r"\d+ (\d+) W (.*)\t(.*)", line)
+    if not m:
+        continue
+    size, name, filename = m.groups()
+    files_by_name.setdefault(name, set()).add(filename)
+    sizes_by_name.setdefault(name, set()).add(int(size))
+
+odr_violations = 0
+for name, sizes in sizes_by_name.items():
+    if len(sizes) == 1:
+        continue
+    files = files_by_name[name]
+    # Ignore symbols that only appear in one file.
+    # These are typically headers - unclear why they get different sizes but it appears benign.
+    if len(files) == 1:
+        continue
+    # Multiple sizes for this symbol name.
+    odr_violations += 1
+    print("Multiple sizes for symbol: " + name)
+    print("\t%s" % ", ".join([str(x) for x in sizes]))
+    print("\tFound in files:")
+    for filename in files:
+        print("\t\t%s" % filename)
+
+if odr_violations == 0:
+    print("No ODR violations found, hooray")
+
+# Show potential weak symbols.
+suspicious_odrs = 0
+for (name, files) in files_by_name.items():
+    if len(files) != 1:
+        continue
+    (filename,) = files
+    if ".cpp" in filename:
+        if suspicious_odrs == 0:
+            print("Some suspicious singles:")
+        suspicious_odrs += 1
+        print("\t%s" % name)
+        print("\t\tIn file %s" % filename)