diff --git a/storm_analysis/__init__.py b/storm_analysis/__init__.py
index 112d47c0..6b3c4a30 100644
--- a/storm_analysis/__init__.py
+++ b/storm_analysis/__init__.py
@@ -4,12 +4,39 @@
 """
 import os
 import matplotlib
+
+#
+# Headless operation.
+#
+# Setting STORM_ANALYSIS_HEADLESS in the environment selects a
+# non-interactive matplotlib backend, which makes every pyplot.show() in
+# the package a no-op. Nothing can then open a window and block, which is
+# what you want when running the diagnostics, or anything else, without
+# someone sitting there to close the windows.
+#
+# This has to happen before pyplot is imported, hence its position here.
+# Saving figures is not affected, savefig() works the same under Agg.
+#
+if os.environ.get("STORM_ANALYSIS_HEADLESS"):
+    matplotlib.use("Agg")
+
 import matplotlib.pyplot as pyplot
 
 
 class SAException(Exception):
     pass
 
+
+def isHeadless():
+    """
+    Return True if we were asked not to open any plot windows.
+
+    Note that this reports the request, not the outcome. matplotlib will
+    also fall back to a non-interactive backend on its own when there is
+    no display available.
+    """
+    return bool(os.environ.get("STORM_ANALYSIS_HEADLESS"))
+
 __version__ = "2026.08.30"
 
 # Maybe there is a builtin function that does this??
diff --git a/storm_analysis/diagnostics/README.txt b/storm_analysis/diagnostics/README.txt
index 44567365..7d318ef5 100644
--- a/storm_analysis/diagnostics/README.txt
+++ b/storm_analysis/diagnostics/README.txt
@@ -21,6 +21,21 @@ changing (1) and (3) as needed, to test analysis performance with different type
 simulated data.
 
 
+Running without a display:
+
+Some of the analysis these call will open a plot window and wait for you to close
+it, which is not what you want when running several diagnostics in a row. Setting
+
+  STORM_ANALYSIS_HEADLESS=1
+
+in the environment selects a non-interactive matplotlib backend, so pyplot.show()
+does nothing anywhere in the package. Figures that are written to disk, such as the
+mapping images from the multicolor diagnostic, are still written.
+
+Note that multiplane/configure.py needs --psf-model, one of psf_fft, pupilfn or
+spline. The rest take no arguments.
+
+
 (Linux) C profiling tools:
 1. http://valgrind.org/docs/manual/cl-manual.html
 2. http://kcachegrind.sourceforge.net/html/Home.html
diff --git a/storm_analysis/diagnostics/frc/analyze_data.py b/storm_analysis/diagnostics/frc/analyze_data.py
index 303e3132..3c6b8051 100644
--- a/storm_analysis/diagnostics/frc/analyze_data.py
+++ b/storm_analysis/diagnostics/frc/analyze_data.py
@@ -22,7 +22,9 @@ def analyzeData():
         frc_text = os.path.join(a_dir, "frc.txt")
 
         # Run FRC analysis.
-        frcCalc2d.frcCalc2d(hdf5, frc_text)
+        # show_plot defaults to True, and this loops over every test
+        # directory, so without this it stops on a window each time.
+        frcCalc2d.frcCalc2d(hdf5, frc_text, show_plot = False)
 
     print()