diff --git a/apps/website/eslint-rules/index.js b/apps/website/eslint-rules/index.js
index e526c75b1..409e554b4 100644
--- a/apps/website/eslint-rules/index.js
+++ b/apps/website/eslint-rules/index.js
@@ -25,11 +25,13 @@ const writeBoundaryRules = require('./write-boundary-rules');
 const modelTaxonomyRules = require('./model-taxonomy-rules');
 const filenameRules = require('./filename-rules');
 const componentNoDataManipulation = require('./component-no-data-manipulation');
+const presenterPurity = require('./presenter-purity');
 
 module.exports = {
   rules: {
     // Presenter Contract
     'presenter-contract': presenterContract,
+    'presenter-purity': presenterPurity,
     
     // RSC Boundary Rules
     'rsc-no-container-manager': rscBoundaryRules['no-container-manager-in-server'],
diff --git a/apps/website/eslint-rules/presenter-contract.js b/apps/website/eslint-rules/presenter-contract.js
index b4a884f06..88181b938 100644
--- a/apps/website/eslint-rules/presenter-contract.js
+++ b/apps/website/eslint-rules/presenter-contract.js
@@ -87,10 +87,11 @@ module.exports = {
 
       // Check for present method in classes
       MethodDefinition(node) {
-        if (presenterClassNode && 
-            node.key.type === 'Identifier' && 
+        if (presenterClassNode &&
+            node.key.type === 'Identifier' &&
             node.key.name === 'present' &&
-            node.parent === presenterClassNode) {
+            node.parent.type === 'ClassBody' &&
+            node.parent.parent === presenterClassNode) {
           hasPresentMethod = true;
         }
       },
diff --git a/apps/website/eslint-rules/presenter-purity.js b/apps/website/eslint-rules/presenter-purity.js
new file mode 100644
index 000000000..24e7bfa3e
--- /dev/null
+++ b/apps/website/eslint-rules/presenter-purity.js
@@ -0,0 +1,53 @@
+/**
+ * ESLint rule: Presenters should only do pure mapping, not business logic
+ * 
+ * Presenters should NOT use:
+ * - .filter() - filtering should happen in PageQuery
+ * - .sort() - sorting should happen in PageQuery  
+ * - .reduce() - aggregation should happen in PageQuery
+ * - .find() - lookup should happen in PageQuery
+ * - .some() / .every() - checks should happen in PageQuery
+ */
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Forbid business logic operations in presenters',
+      category: 'Presenter Purity',
+    },
+    messages: {
+      message: 'Presenter should only do pure mapping. Move {{operation}}() to PageQuery - see apps/website/lib/contracts/presenters/Presenter.ts',
+    },
+  },
+  create(context) {
+    return {
+      CallExpression(node) {
+        const filename = context.getFilename();
+        
+        // Check if this is a presenter file
+        if (filename.includes('/lib/presenters/') && filename.endsWith('.ts')) {
+          
+          // Check for business logic operations
+          if (node.callee.type === 'MemberExpression') {
+            const property = node.callee.property;
+            
+            if (property.type === 'Identifier') {
+              const forbiddenOperations = ['filter', 'sort', 'reduce', 'find', 'some', 'every', 'map'];
+              const operation = property.name;
+              
+              // Allow .map() - that's the core presenter operation
+              if (forbiddenOperations.includes(operation) && operation !== 'map') {
+                context.report({
+                  node,
+                  messageId: 'message',
+                  data: { operation },
+                });
+              }
+            }
+          }
+        }
+      },
+    };
+  },
+};
\ No newline at end of file