diff --git a/slides_template/README b/slides_template/README
index a28e56d..894d556 100644
--- a/slides_template/README
+++ b/slides_template/README
@@ -46,6 +46,45 @@ everything needed.
 The template uses the Metropolis Beamer theme, bundled in the template/
 directory along with the OpenSans and RobotoMono fonts it requires.
 
+================================
+=== Accessibility ==============
+================================
+
+Slides are built as tagged PDFs that validate against PDF/UA-2
+(ISO 14289-2), which is what upload targets like Canvas check for. Check
+a file with veraPDF (https://verapdf.org/):
+
+  verapdf -f ua2 my-talk.pdf
+
+The pieces that do this work are:
+
+  * \DocumentMetadata declares PDF/UA-2, PDF 2.0, and the document
+    language. The language tag tells a screen reader how to pronounce
+    the text.
+  * tagpdf with activate-all turns tagging on.
+  * The frametitle template is patched to emit H1 tags, since Beamer
+    does not treat frame titles as headings on its own.
+  * unicode-math replaces the Computer Modern math fonts, which carry no
+    Unicode mappings and leave formulas unreadable to assistive software.
+  * \hypersetup{pdfdisplaydoctitle=true} makes viewers announce the
+    document title instead of the filename.
+  * The tikz overlays behind \credit, \marktopleft, and \markbottomright
+    are marked as artifacts so they stay out of the reading order.
+
+Use a slides-only build (make slides) for anything shared. Builds that
+include speaker notes do not validate, because Beamer repeats the frame
+title and section headings on the notes half of each page.
+
+Validating is not the same as being accessible, and this template does
+the first better than the second. Frame titles and links are tagged;
+body text, lists, and figures are not, so a screen reader gets the
+outline of a talk rather than its contents. Closing that gap needs
+automatic tagging from the LaTeX kernel (\DocumentMetadata{tagging=on}),
+which requires TeX Live 2025 or later and is waiting on Overleaf to
+support it, and Beamer support in the LaTeX Tagging Project, which does
+not exist yet. The alt={...} arguments in the template are written for
+that day; they are dropped by the current toolchain.
+
 ================================
 === Scripts ====================
 ================================
diff --git a/slides_template/example.tex b/slides_template/example.tex
index 325b48f..ebeef9f 100644
--- a/slides_template/example.tex
+++ b/slides_template/example.tex
@@ -153,6 +153,8 @@ BoldItalicFont  =   *-BoldItalic
 }
 
 % packages i use in essentially every document
+% give every \includegraphics an alt={...} description. the current
+% toolchain drops it, but it will be used once tagging is available
 \usepackage{graphicx}
 \usepackage{url}
 % \usepackage{dcolumn}