diff --git a/third_party/py/frozendict/frozendict/__init__.py b/third_party/py/frozendict/frozendict/__init__.py
index 399948a61b597b..cf51bcbbef40a8 100644
--- a/third_party/py/frozendict/frozendict/__init__.py
+++ b/third_party/py/frozendict/frozendict/__init__.py
@@ -9,11 +9,15 @@
 except ImportError:  # python < 2.7
     OrderedDict = NotImplemented
 
+try:
+    from collections import Mapping
+except ImportError:
+    from collections.abc import Mapping
 
 iteritems = getattr(dict, 'iteritems', dict.items) # py2-3 compatibility
 
 
-class frozendict(collections.Mapping):
+class frozendict(Mapping):
     """
     An immutable wrapper around dictionaries that implements the complete :py:class:`collections.Mapping`
     interface. It can be used as a drop-in replacement for dictionaries where immutability is desired.
diff --git a/tools/ctexplain/analyses/summary.py b/tools/ctexplain/analyses/summary.py
index 6669e6c5216445..e99a582016c13c 100644
--- a/tools/ctexplain/analyses/summary.py
+++ b/tools/ctexplain/analyses/summary.py
@@ -20,6 +20,8 @@
 from tools.ctexplain.types import ConfiguredTarget
 # Do not edit this line. Copybara replaces it with PY2 migration helper..third_party.bazel.tools.ctexplain.util as util
 
+import tools.ctexplain.util as util
+
 
 @dataclass(frozen=True)
 class _Summary():
diff --git a/tools/ctexplain/bazel_api.py b/tools/ctexplain/bazel_api.py
index 02a16174a6eb02..9d78986a56c664 100644
--- a/tools/ctexplain/bazel_api.py
+++ b/tools/ctexplain/bazel_api.py
@@ -15,8 +15,10 @@
 
 There's no Python Bazel API so we invoke Bazel as a subprocess.
 """
+import functools
 import json
 import os
+import re
 import subprocess
 from typing import Callable
 from typing import List
@@ -28,8 +30,12 @@
 from tools.ctexplain.types import HostConfiguration
 from tools.ctexplain.types import NullConfiguration
 
+CQUERY_RESULT_LINE_REGEX = re.compile(r"^(.*?) \((\S+)\) \[([^[]*)\]$")
+DEFAULT_BAZEL_BINARY = "bazel"
 
-def run_bazel_in_client(args: List[str]) -> Tuple[int, List[str], List[str]]:
+
+def run_bazel_in_client(args: List[str],
+                        bazel: str = DEFAULT_BAZEL_BINARY) -> Tuple[int, List[str], List[str]]:
   """Calls bazel within the current workspace.
 
   For production use. Tests use an alternative invoker that goes through test
@@ -42,7 +48,7 @@ def run_bazel_in_client(args: List[str]) -> Tuple[int, List[str], List[str]]:
     Tuple of (return code, stdout, stderr)
   """
   result = subprocess.run(
-      ["blaze"] + args,
+      [bazel] + args,
       cwd=os.getcwd(),
       stdout=subprocess.PIPE,
       stderr=subprocess.PIPE,
@@ -57,8 +63,12 @@ class BazelApi():
   def __init__(self,
                run_bazel: Callable[[List[str]],
                                    Tuple[int, List[str],
-                                         List[str]]] = run_bazel_in_client):
+                                         List[str]]] = None,
+               bazel: str = DEFAULT_BAZEL_BINARY):
+    self.bazel = bazel
     self.run_bazel = run_bazel
+    if run_bazel is None:
+      self.run_bazel = functools.partial(run_bazel_in_client, bazel=self.bazel)
 
   def cquery(self,
              args: List[str]) -> Tuple[bool, str, Tuple[ConfiguredTarget, ...]]:
@@ -144,20 +154,13 @@ def _parse_cquery_result_line(line: str) -> ConfiguredTarget:
   Returns:
     Corresponding ConfiguredTarget if the line matches else None.
   """
-  tokens = line.split(maxsplit=2)
-  label = tokens[0]
-  if tokens[1][0] != "(" or tokens[1][-1] != ")":
-    raise ValueError(f"{tokens[1]} in {line} not surrounded by parentheses")
-  config_hash = tokens[1][1:-1]
-  if config_hash == "null":
-    fragments = ()
-  else:
-    if tokens[2][0] != "[" or tokens[2][-1] != "]":
-      raise ValueError(f"{tokens[2]} in {line} not surrounded by [] brackets")
-    # The fragments list looks like '[Fragment1, Fragment2, ...]'. Split the
-    # whole line on ' [' to get just this list, then remove the final ']', then
-    # split again on ', ' to convert it to a structured tuple.
-    fragments = tuple(line.split(" [")[1][0:-1].split(", "))
+  result = CQUERY_RESULT_LINE_REGEX.search(line)
+  if result is None:
+    raise ValueError(f"{repr(line)} does not match {repr(CQUERY_RESULT_LINE_REGEX.pattern)}")
+  label, config_hash, fragments_str = result.groups()
+  # The fragments list looks like 'Fragment1, Fragment2, ...'. Split on
+  # ', ' to convert it to a structured tuple.
+  fragments = tuple(fragments_str.split(", "))
   return ConfiguredTarget(
       label=label,
       config=None,  # Not yet available: we'll need `bazel config` to get this.
diff --git a/tools/ctexplain/ctexplain.py b/tools/ctexplain/ctexplain.py
index 65814799a35cb1..4798a943ff0594 100644
--- a/tools/ctexplain/ctexplain.py
+++ b/tools/ctexplain/ctexplain.py
@@ -43,11 +43,15 @@
 from dataclasses import dataclass
 
 # Do not edit this line. Copybara replaces it with PY2 migration helper..third_party.bazel.tools.ctexplain.analyses.summary as summary
-from tools.ctexplain.bazel_api import BazelApi
+from tools.ctexplain.bazel_api import DEFAULT_BAZEL_BINARY, BazelApi
 # Do not edit this line. Copybara replaces it with PY2 migration helper..third_party.bazel.tools.ctexplain.lib as lib
 from tools.ctexplain.types import ConfiguredTarget
 # Do not edit this line. Copybara replaces it with PY2 migration helper..third_party.bazel.tools.ctexplain.util as util
 
+import tools.ctexplain.lib as lib
+import tools.ctexplain.util as util
+import tools.ctexplain.analyses.summary as summary
+
 FLAGS = flags.FLAGS
 
 
@@ -112,6 +116,8 @@ def _render_analysis_help_text() -> str:
     lambda flag_value: all(name in analyses for name in flag_value),
     message=f'available analyses: {", ".join(analyses.keys())}')
 
+flags.DEFINE_string("bazel", DEFAULT_BAZEL_BINARY, "Path to bazel binary")
+
 flags.DEFINE_multi_string(
     "build", [],
     """command-line invocation of the build to analyze. For example:
@@ -133,8 +139,8 @@ def _get_build_flags(cmdline: str) -> Tuple[Tuple[str, ...], Tuple[str, ...]]:
     Tuple of ((target labels to build), (build flags))
   """
   cmdlist = cmdline.split()
-  labels = [arg for arg in cmdlist if arg.startswith("//")]
-  build_flags = [arg for arg in cmdlist if not arg.startswith("//")]
+  labels = [arg for arg in cmdlist if arg.startswith("//") or arg.startswith("@")]
+  build_flags = [arg for arg in cmdlist if not arg.startswith("//") and not arg.startswith("@")]
   return (tuple(labels), tuple(build_flags))
 
 
@@ -148,8 +154,10 @@ def main(argv):
 
   (labels, build_flags) = _get_build_flags(FLAGS.build[0])
   build_desc = ",".join(labels)
+
   with util.ProgressStep(f"Collecting configured targets for {build_desc}"):
-    cts = lib.analyze_build(BazelApi(), labels, build_flags)
+    cts = lib.analyze_build(BazelApi(bazel=FLAGS.bazel), labels, build_flags)
+
   for analysis in FLAGS.analysis:
     analyses[analysis].exec(cts)
 
diff --git a/tools/ctexplain/lib.py b/tools/ctexplain/lib.py
index 172509d1c75f35..a97ded928df2ea 100644
--- a/tools/ctexplain/lib.py
+++ b/tools/ctexplain/lib.py
@@ -16,6 +16,7 @@
 
 # Do not edit this line. Copybara replaces it with PY2 migration helper..third_party.bazel.tools.ctexplain.bazel_api as bazel_api
 from tools.ctexplain.types import ConfiguredTarget
+import tools.ctexplain.bazel_api as bazel_api
 
 
 def analyze_build(bazel: bazel_api.BazelApi, labels: Tuple[str, ...],