diff --git a/x-pack/plugins/observability/public/components/threshold/components/custom_equation/custom_equation_editor.tsx b/x-pack/plugins/observability/public/components/threshold/components/custom_equation/custom_equation_editor.tsx
index cdb4f7b7155a0..8dbb44eda71dd 100644
--- a/x-pack/plugins/observability/public/components/threshold/components/custom_equation/custom_equation_editor.tsx
+++ b/x-pack/plugins/observability/public/components/threshold/components/custom_equation/custom_equation_editor.tsx
@@ -9,6 +9,7 @@ import {
   EuiFormRow,
   EuiFlexItem,
   EuiFlexGroup,
+  EuiIconTip,
   EuiButtonEmpty,
   EuiSpacer,
   EuiExpression,
@@ -193,10 +194,23 @@ export function CustomEquationEditor({
         >
           <div>
             <ClosablePopoverTitle onClose={() => setCustomEqPopoverOpen(false)}>
-              <FormattedMessage
-                id="xpack.observability.threshold.rule.alertFlyout.customEquationLabel"
-                defaultMessage="Custom equation"
-              />
+              <span>
+                <FormattedMessage
+                  id="xpack.observability.threshold.rule.alertFlyout.customEquationLabel"
+                  defaultMessage="Custom equation"
+                />
+                &nbsp;
+                <EuiIconTip
+                  content={i18n.translate(
+                    'xpack.observability.threshold.rule.alertFlyout.customEquationTooltip',
+                    {
+                      defaultMessage:
+                        'This supports basic math (A + B / C) and boolean logic (A < B ? A : B).',
+                    }
+                  )}
+                  position="top"
+                />
+              </span>
             </ClosablePopoverTitle>
             <EuiFormRow
               fullWidth
diff --git a/x-pack/plugins/observability/public/components/threshold/i18n_strings.ts b/x-pack/plugins/observability/public/components/threshold/i18n_strings.ts
index ae70754dad545..0c480fbb9fb28 100644
--- a/x-pack/plugins/observability/public/components/threshold/i18n_strings.ts
+++ b/x-pack/plugins/observability/public/components/threshold/i18n_strings.ts
@@ -9,7 +9,10 @@ import { i18n } from '@kbn/i18n';
 
 export const EQUATION_HELP_MESSAGE = i18n.translate(
   'xpack.observability.threshold.rule.alertFlyout.customEquationEditor.equationHelpMessage',
-  { defaultMessage: 'Supports basic math expressions' }
+  {
+    defaultMessage:
+      'Supports basic math equations, valid charaters are: A-Z, +, -, /, *, (, ), ?, !, &, :, |, >, <, =',
+  }
 );
 
 export const LABEL_LABEL = i18n.translate(