diff --git a/swh/docs/sphinx/conf.py b/swh/docs/sphinx/conf.py
--- a/swh/docs/sphinx/conf.py
+++ b/swh/docs/sphinx/conf.py
@@ -31,6 +31,7 @@
     "sphinx_click.ext",
     "myst_parser",
     "sphinx.ext.todo",
+    "swh.docs.sphinx.view_in_phabricator",
 ]
 
 # Add any paths that contain templates here, relative to this directory.
diff --git a/swh/docs/sphinx/view_in_phabricator.py b/swh/docs/sphinx/view_in_phabricator.py
new file mode 100644
--- /dev/null
+++ b/swh/docs/sphinx/view_in_phabricator.py
@@ -0,0 +1,31 @@
+# Copyright (C) 2021  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+"""
+Shows a link 'View this page in Phabricator' on top of each page.
+"""
+
+
+def html_page_context(app, pagename, templatename, context, doctree):
+    if pagename.startswith("apidoc/"):
+        # Auto-generated documentation.
+        # TODO: link to the .py
+        context["show_source"] = False
+        return
+    elif pagename.startswith("swh-"):
+        # .rst from a package's docs/ directory
+        repository = pagename.split("/", 1)[0]
+        path = "docs/"
+    else:
+        # .rst from swh-docs/docs/
+        repository = "swh-docs"
+        path = "docs/"
+    context[
+        "source_url_prefix"
+    ] = f"https://forge.softwareheritage.org/source/{repository}/browse/master/{path}"
+
+
+def setup(app):
+    app.connect("html-page-context", html_page_context)