diff --git a/datasette/permissions.py b/datasette/permissions.py
new file mode 100644
index 00000000..91c9e774
--- /dev/null
+++ b/datasette/permissions.py
@@ -0,0 +1,19 @@
+import collections
+
+Permission = collections.namedtuple(
+    "Permission", ("name", "abbr", "takes_database", "takes_table", "default")
+)
+
+PERMISSIONS = (
+    Permission("view-instance", "vi", False, False, True),
+    Permission("view-database", "vd", True, False, True),
+    Permission("view-database-download", "vdd", True, False, True),
+    Permission("view-table", "vt", True, True, True),
+    Permission("view-query", "vq", True, True, True),
+    Permission("insert-row", "ir", True, True, False),
+    Permission("delete-row", "dr", True, True, False),
+    Permission("drop-table", "dt", True, True, False),
+    Permission("execute-sql", "es", True, False, True),
+    Permission("permissions-debug", "pd", False, False, False),
+    Permission("debug-menu", "dm", False, False, False),
+)
diff --git a/datasette/templates/permissions_debug.html b/datasette/templates/permissions_debug.html
index b0f50f0e..36a12acc 100644
--- a/datasette/templates/permissions_debug.html
+++ b/datasette/templates/permissions_debug.html
@@ -19,11 +19,97 @@
 .check-action, .check-when, .check-result {
     font-size: 1.3em;
 }
+textarea {
+    height: 10em;
+    width: 95%;
+    box-sizing: border-box;
+    padding: 0.5em;
+    border: 2px dotted black;
+}
+.two-col {
+    display: inline-block;
+    width: 48%;
+}
+.two-col label {
+    width: 48%;
+}
+@media only screen and (max-width: 576px) {
+    .two-col {
+        width: 100%;
+    }
+}
 </style>
 {% endblock %}
 
 {% block content %}
 
+<h1>Permission check testing tool</h1>
+
+<p>This tool lets you simulate an actor and a permission check for that actor.</p>
+
+<form action="{{ urls.path('-/permissions') }}" id="debug-post" method="post" style="margin-bottom: 1em">
+    <input type="hidden" name="csrftoken" value="{{ csrftoken() }}">
+    <div class="two-col">
+        <p><label>Actor</label></p>
+        <textarea name="actor">{% if actor_input %}{{ actor_input }}{% else %}{"id": "root"}{% endif %}</textarea>
+    </div>
+    <div class="two-col" style="vertical-align: top">
+        <p><label for="permission" style="display:block">Permission</label>
+        <select name="permission" id="permission">
+            {% for permission in permissions %}
+                <option value="{{ permission.0 }}">{{ permission.name }} (default {{ permission.default }})</option>
+            {% endfor %}
+        </select>
+        <p><label for="resource_1">Database name</label><input type="text" id="resource_1" name="resource_1"></p>
+        <p><label for="resource_2">Table or query name</label><input type="text" id="resource_2" name="resource_2"></p>
+    </div>
+    <div style="margin-top: 1em;">
+        <input type="submit" value="Simulate permission check">
+    </div>
+    <pre style="margin-top: 1em" id="debugResult"></pre>
+</form>
+
+<script>
+var rawPerms = {{ permissions|tojson }};
+var permissions = Object.fromEntries(rawPerms.map(([label, abbr, needs_resource_1, needs_resource_2, def]) => [label, {needs_resource_1, needs_resource_2, def}]))
+var permissionSelect = document.getElementById('permission');
+var resource1 = document.getElementById('resource_1');
+var resource2 = document.getElementById('resource_2');
+function updateResourceVisibility() {
+    var permission = permissionSelect.value;
+    var {needs_resource_1, needs_resource_2} = permissions[permission];
+    if (needs_resource_1) {
+        resource1.closest('p').style.display = 'block';
+    } else {
+        resource1.closest('p').style.display = 'none';
+    }
+    if (needs_resource_2) {
+        resource2.closest('p').style.display = 'block';
+    } else {
+        resource2.closest('p').style.display = 'none';
+    }
+}
+permissionSelect.addEventListener('change', updateResourceVisibility);
+updateResourceVisibility();
+
+// When #debug-post form is submitted, use fetch() to POST data
+var debugPost = document.getElementById('debug-post');
+var debugResult = document.getElementById('debugResult');
+debugPost.addEventListener('submit', function(ev) {
+    ev.preventDefault();
+    var formData = new FormData(debugPost);
+    console.log(formData);
+    fetch(debugPost.action, {
+        method: 'POST',
+        body: new URLSearchParams(formData),
+    }).then(function(response) {
+        return response.json();
+    }).then(function(data) {
+        debugResult.innerText = JSON.stringify(data, null, 4);
+    });
+});
+</script>
+
 <h1>Recent permissions checks</h1>
 
 {% for check in permission_checks %}
diff --git a/datasette/views/special.py b/datasette/views/special.py
index 9922a621..ff014246 100644
--- a/datasette/views/special.py
+++ b/datasette/views/special.py
@@ -1,6 +1,8 @@
 import json
+from datasette.permissions import PERMISSIONS
 from datasette.utils.asgi import Response, Forbidden
 from datasette.utils import actor_matches_allow, add_cors_headers
+from datasette.permissions import PERMISSIONS
 from .base import BaseView
 import secrets
 import time
@@ -103,7 +105,37 @@ class PermissionsDebugView(BaseView):
             ["permissions_debug.html"],
             request,
             # list() avoids error if check is performed during template render:
-            {"permission_checks": list(reversed(self.ds._permission_checks))},
+            {
+                "permission_checks": list(reversed(self.ds._permission_checks)),
+                "permissions": PERMISSIONS,
+            },
+        )
+
+    async def post(self, request):
+        await self.ds.ensure_permissions(request.actor, ["view-instance"])
+        if not await self.ds.permission_allowed(request.actor, "permissions-debug"):
+            raise Forbidden("Permission denied")
+        vars = await request.post_vars()
+        actor = json.loads(vars["actor"])
+        permission = vars["permission"]
+        resource_1 = vars["resource_1"]
+        resource_2 = vars["resource_2"]
+        resource = []
+        if resource_1:
+            resource.append(resource_1)
+        if resource_2:
+            resource.append(resource_2)
+        resource = tuple(resource)
+        result = await self.ds.permission_allowed(
+            actor, permission, resource, default="USE_DEFAULT"
+        )
+        return Response.json(
+            {
+                "actor": actor,
+                "permission": permission,
+                "resource": resource,
+                "result": result,
+            }
         )