diff --git a/.gitignore b/.gitignore
index 4b3a324f690d..c4412761d11f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,9 @@
 
 # VSCode creates this directory in ways that are hard to prevent.
 /.vscode/
+
+# Directories created by clangd
+/.cache/clangd
+
+# Compilation database used by clangd
+compile_commands.json
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index b30f683fdbc7..01f1fe8480fd 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -17,7 +17,7 @@ repos:
       - id: check-executables-have-shebangs
       - id: check-merge-conflict
       - id: check-symlinks
-        exclude: '^website/jekyll/site/_includes$'
+        exclude: '^(website/jekyll/site/_includes|bazel-(clang-toolchain|execroot))$'
       - id: check-yaml
       - id: detect-private-key
       - id: end-of-file-fixer
diff --git a/bazel-clang-toolchain b/bazel-clang-toolchain
new file mode 120000
index 000000000000..527bc7f3f50a
--- /dev/null
+++ b/bazel-clang-toolchain
@@ -0,0 +1 @@
+bazel-out/../../../external/bootstrap_clang_toolchain
\ No newline at end of file
diff --git a/bazel-execroot b/bazel-execroot
new file mode 120000
index 000000000000..729d2688d5a9
--- /dev/null
+++ b/bazel-execroot
@@ -0,0 +1 @@
+bazel-out/../../carbon
\ No newline at end of file
diff --git a/compile_flags.txt b/compile_flags.txt
index 45e81de98cdf..4f7ffc5af025 100644
--- a/compile_flags.txt
+++ b/compile_flags.txt
@@ -43,35 +43,38 @@
 -iquote
 bazel-bin
 -iquote
-bazel-carbon-lang/external/llvm-project
+bazel-execroot/external/llvm-project
 -iquote
 bazel-bin/external/llvm-project
 -iquote
-bazel-carbon-lang/external/llvm_terminfo
+bazel-execroot/external/llvm_terminfo
 -iquote
 bazel-bin/external/llvm_terminfo
 -iquote
-bazel-carbon-lang/external/llvm_zlib
+bazel-execroot/external/llvm_zlib
 -iquote
 bazel-bin/external/llvm_zlib
 -iquote
-bazel-carbon-lang/external/bazel_tools
+bazel-execroot/external/bazel_tools
 -iquote
 bazel-bin/external/bazel_tools
--Ibazel-bin/external/llvm-project/llvm/_virtual_includes/gtest_internal_headers
+-Ibazel-execroot/external/llvm-project/llvm/utils/unittest/googletest/src
 -isystem
-bazel-carbon-lang/external/llvm-project/llvm/include
+bazel-execroot/external/llvm-project/llvm/include
 -isystem
 bazel-bin/external/llvm-project/llvm/include
 -isystem
-bazel-carbon-lang/external/llvm-project/llvm/utils/unittest/googlemock/include
+bazel-execroot/external/llvm-project/llvm/utils/unittest/googlemock/include
 -isystem
 bazel-bin/external/llvm-project/llvm/utils/unittest/googlemock/include
 -isystem
-bazel-carbon-lang/external/llvm-project/llvm/utils/unittest/googletest/include
+bazel-execroot/external/llvm-project/llvm/utils/unittest/googletest/include
 -isystem
 bazel-bin/external/llvm-project/llvm/utils/unittest/googletest/include
 -std=c++17
+-nostdinc++
+-isystem
+bazel-clang-toolchain/include/c++/v1
 -no-canonical-prefixes
 -Wno-builtin-macro-redefined
 -D__DATE__="redacted"
diff --git a/scripts/create_compdb.py b/scripts/create_compdb.py
new file mode 100755
index 000000000000..1d47e2989af0
--- /dev/null
+++ b/scripts/create_compdb.py
@@ -0,0 +1,156 @@
+#!/usr/bin/env python3
+
+"""Create a compilation database for Clang tools like `clangd`.
+
+If you want `clangd` to be able to index this project, run this script from
+the workspace root to generate a rich compilation database. After the first
+run, you should only need to run it if you encounter `clangd` problems, or if
+you want `clangd` to build an up-to-date index of the entire project. Note
+that in the latter case you may need to manually clear and rebuild clangd's
+index after running this script.
+
+Note that this script will build generated files in the Carbon project and
+otherwise touch the Bazel build. It works to do the minimum amount necessary.
+Once setup, generally subsequent builds, even of small parts of the project,
+different configurations, or that hit errors won't disrupt things. But, if
+you do hit errors, you can get things back to a good state by fixing the
+build of generated files and re-running this script.
+"""
+
+__copyright__ = """
+Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+Exceptions. See /LICENSE for license information.
+SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+"""
+
+import json
+import os
+import re
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+
+# Change the working directory to the repository root so that the remaining
+# operations reliably operate relative to that root.
+os.chdir(Path(__file__).parent.parent)
+directory = Path.cwd()
+
+# We use the `BAZEL` environment variable if present. If not, then we try to
+# use `bazelisk` and then `bazel`.
+bazel = os.environ.get("BAZEL")
+if not bazel:
+    bazel = "bazelisk"
+    if not shutil.which(bazel):
+        bazel = "bazel"
+        if not shutil.which(bazel):
+            sys.exit("Unable to run Bazel")
+
+# Load compiler flags. We do this first in order to fail fast if not run from
+# the workspace root.
+print("Reading the arguments to use...")
+try:
+    with open("compile_flags.txt") as flag_file:
+        arguments = [line.strip() for line in flag_file]
+except FileNotFoundError:
+    sys.exit(Path(sys.argv[0]).name + " must be run from the project root")
+
+# Prepend the `clang` executable path to the arguments that looks into our
+# downloaded Clang toolchain.
+arguments = [str(Path("bazel-clang-toolchain/bin/clang"))] + arguments
+
+print("Building compilation database...")
+
+# Find all of the C++ source files that we expect to compile cleanly as
+# stand-alone files. This is a bit simpler than scraping the actual compile
+# actions and allows us to directly index header-only libraries easily and
+# pro-actively index the specific headers in the project.
+source_files_query = subprocess.run(
+    [
+        bazel,
+        "query",
+        "--keep_going",
+        "--output=location",
+        'filter(".*\\.(h|cpp|cc|c|cxx)$", kind("source file", deps(//...)))',
+    ],
+    check=True,
+    stdout=subprocess.PIPE,
+    stderr=subprocess.DEVNULL,
+    universal_newlines=True,
+).stdout
+source_files = [
+    Path(line.split(":")[0]) for line in source_files_query.splitlines()
+]
+
+# Filter into the Carbon source files that we'll find directly in the
+# workspace, and LLVM source files that need to be mapped through the merged
+# LLVM tree in Bazel's execution root.
+carbon_files = [
+    f.relative_to(directory)
+    for f in source_files
+    if f.parts[: len(directory.parts)] == directory.parts
+]
+llvm_files = [
+    Path("bazel-execroot/external").joinpath(
+        *f.parts[f.parts.index("llvm-project") :]
+    )
+    for f in source_files
+    if "llvm-project" in f.parts
+]
+print(
+    "Found %d Carbon source files and %d LLVM source files..."
+    % (len(carbon_files), len(llvm_files))
+)
+
+# Now collect the generated file labels.
+generated_file_labels = subprocess.run(
+    [
+        bazel,
+        "query",
+        "--keep_going",
+        "--output=label",
+        (
+            'filter(".*\\.(h|cpp|cc|c|cxx|def|inc)$",'
+            'kind("generated file", deps(//...)))'
+        ),
+    ],
+    check=True,
+    stdout=subprocess.PIPE,
+    stderr=subprocess.DEVNULL,
+    universal_newlines=True,
+).stdout.splitlines()
+print("Found %d generated files..." % (len(generated_file_labels),))
+
+# Directly build these labels so that indexing can find them. Allow this to
+# fail in case there are build errors in the client, and just warn the user
+# that they may be missing generated files.
+print("Building the generated files so that tools can find them...")
+subprocess.run([bazel, "build", "--keep_going"] + generated_file_labels)
+
+
+# Manually translate the label to a user friendly path into the Bazel output
+# symlinks.
+def _label_to_path(s):
+    # Map external repositories to their part of the output tree.
+    s = re.sub(r"^@([^/]+)//", r"bazel-bin/external/\1/", s)
+    # Map this repository to the root of the output tree.
+    s = s if not s.startswith("//") else "bazel-bin/" + s[len("//") :]
+    # Replace the colon used to mark the package name with a slash.
+    s = s.replace(":", "/")
+    # Convert to a native path.
+    return Path(s)
+
+
+generated_files = [_label_to_path(label) for label in generated_file_labels]
+
+# Generate compile_commands.json with an entry for each C++ input.
+entries = [
+    {
+        "directory": str(directory),
+        "file": str(f),
+        "arguments": arguments + [str(f)],
+    }
+    for f in carbon_files + llvm_files + generated_files
+]
+with open("compile_commands.json", "w") as json_file:
+    json.dump(entries, json_file, indent=2)
diff --git a/setup.cfg b/setup.cfg
index 481144013d90..2ce5f1e8ff18 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -5,6 +5,7 @@
 [flake8]
 max-line-length = 80
 exclude = website/jekyll/build
+# E203: This warning is not PEP 8 compliant.
 # E402: Allow the pythonpath modifications before repo-local imports.
 # W503: flake8 v3.8.4 is inconsistent with black v20.8b1 (pre-commit run -a).
-ignore = E402,W503
+ignore = E203,E402,W503