diff --git a/nix/ci-env.nix b/nix/ci-env.nix
index c33c4d6d21..ddc7a6a732 100644
--- a/nix/ci-env.nix
+++ b/nix/ci-env.nix
@@ -7,7 +7,7 @@
   ...
 }:
 let
-  inherit (import ./packages.nix { inherit pkgs; }) commonPackages;
+  inherit (import ./packages.nix { inherit pkgs customGlibc; }) commonPackages;
 
   # Each forces something absent on the other platform, so both stay lazy.
   linux = import ./linux.nix { inherit pkgs customGlibc; };
diff --git a/nix/devshell.nix b/nix/devshell.nix
index 25fc73215f..4ccc9ec2e3 100644
--- a/nix/devshell.nix
+++ b/nix/devshell.nix
@@ -31,6 +31,9 @@ let
   };
   customGccGcov = if pkgs.stdenv.hostPlatform.isLinux then linux.gcov else plainGcov;
 
+  # commonPackages whose clang tools parse with the custom toolchain's headers.
+  customCommonPackages = (import ./packages.nix { inherit pkgs customGlibc; }).commonPackages;
+
   # Whole directory: init.sh locates the profiles relative to itself.
   conanDir = ../conan;
 
@@ -86,11 +89,11 @@ let
       version ? null,
       versionedTools ? [ ],
       extraPackages ? [ ],
-      warningHook ? "",
-      # Opt out of PatchNixBinary.cmake retargeting binaries to the system
-      # loader. The plain toolchain links a newer glibc, so it must not be
-      # patched; the custom toolchain patches by default.
-      noPatchNixBinary ? false,
+      # The stock nixpkgs toolchain: warn that it doesn't match CI, keep the
+      # clang tools off the custom toolchain, and opt out of PatchNixBinary.cmake
+      # retargeting binaries to the system loader (the plain toolchain links a
+      # newer glibc, so it must not be patched).
+      plain ? false,
     }:
     let
       compilerVersionHook =
@@ -110,7 +113,8 @@ let
     in
     (pkgs.mkShell.override { inherit stdenv; }) (
       {
-        packages = commonPackages ++ versionedLinks ++ extraPackages;
+        packages =
+          (if plain then commonPackages else customCommonPackages) ++ versionedLinks ++ extraPackages;
         # Marks a managed dev shell, so the build (XrplSanity.cmake) can tell an
         # intentional Nix toolchain from one leaked into a bare shell.
         XRPL_DEVSHELL = shellName;
@@ -119,10 +123,10 @@ let
           ${compilerVersionHook}
           ${darwinLibresolvHook}
           ${conanHook}
-          ${warningHook}
+          ${pkgs.lib.optionalString plain plainWarningHook}
         '';
       }
-      // pkgs.lib.optionalAttrs noPatchNixBinary { XRPLD_NO_PATCH_NIX_BINARY = "1"; }
+      // pkgs.lib.optionalAttrs plain { XRPLD_NO_PATCH_NIX_BINARY = "1"; }
     );
 in
 rec {
@@ -180,8 +184,7 @@ rec {
     version = gccVersion;
     versionedTools = gccVersionedTools;
     extraPackages = [ plainGcov ];
-    warningHook = plainWarningHook;
-    noPatchNixBinary = true;
+    plain = true;
   };
 
   clang-plain = makeShell {
@@ -190,7 +193,6 @@ rec {
     compilerName = "clang";
     version = llvmVersion;
     versionedTools = clangVersionedTools;
-    warningHook = plainWarningHook;
-    noPatchNixBinary = true;
+    plain = true;
   };
 }
diff --git a/nix/linux.nix b/nix/linux.nix
index ea808fbf50..9d39b942a5 100644
--- a/nix/linux.nix
+++ b/nix/linux.nix
@@ -146,6 +146,7 @@ in
     })
   ];
 
+  clang = customClang;
   gccStdenv = customStdenv;
   clangStdenv = pkgs.stdenvAdapters.overrideCC pkgs.stdenv customClang;
   gcov = customGcov;
diff --git a/nix/packages.nix b/nix/packages.nix
index 9af230097d..9925c0201e 100644
--- a/nix/packages.nix
+++ b/nix/packages.nix
@@ -1,4 +1,10 @@
-{ pkgs }:
+{
+  pkgs,
+  # With the custom glibc, the clang tools (clang-tidy, ...) parse code with the
+  # Linux custom toolchain's headers, i.e. the same glibc and libstdc++ as the
+  # build. Without it, they use the nixpkgs default compiler's.
+  customGlibc ? null,
+}:
 let
   # Compiler versions used across the dev shell and the CI environment.
   gccVersion = 15;
@@ -8,7 +14,12 @@ let
   llvmPackages = pkgs."llvmPackages_${toString llvmVersion}";
 
   # Bound explicitly so it tracks llvmPackages above, not the `with pkgs` default.
-  clangTools = llvmPackages.clang-tools;
+  # isLinux first: darwin must not evaluate the custom glibc.
+  clangTools = llvmPackages.clang-tools.override (
+    pkgs.lib.optionalAttrs (pkgs.stdenv.hostPlatform.isLinux && customGlibc != null) {
+      inherit (import ./linux.nix { inherit pkgs customGlibc; }) clang;
+    }
+  );
 
   # In LLVM 22, run-clang-tidy.py moved from share/clang/ to bin/, so nixpkgs
   # clang-tools no longer links it. Wrap it manually.
@@ -112,6 +123,7 @@ in
       gnumake
       gnupg # needed for signing commits & codecov/codecov-action
       graphviz
+      jq
       less # needed for git diff
       mold
       nettools # provides netstat, used to debug failures in CI