diff --git a/_package-export/CLAUDE.md b/_package-export/CLAUDE.md
index 47256f2..8907277 100644
--- a/_package-export/CLAUDE.md
+++ b/_package-export/CLAUDE.md
@@ -40,6 +40,10 @@ The component exposes these callback props (added in 1.2.0):
 
 **API stability**: These are public contracts. Changing signatures or removing callbacks is a breaking change requiring a major version bump.
 
+**1.4.0 additions:**
+- `sourceAttribute` prop - configurable source detection attribute
+- `sourceFile`, `sourceComponent` on Annotation type
+
 **Expansion ideas** (for future consideration):
 - `onActivate` / `onDeactivate` - toolbar state changes
 - `getAnnotations()` ref method - programmatic access
diff --git a/_package-export/README.md b/_package-export/README.md
index 08544bc..47ce5a0 100644
--- a/_package-export/README.md
+++ b/_package-export/README.md
@@ -33,6 +33,7 @@ The toolbar appears in the bottom-right corner. Click to activate, then click an
 - **Area selection** – Drag to annotate any region, even empty space
 - **Animation pause** – Freeze CSS animations to capture specific states
 - **Structured output** – Copy markdown with selectors, positions, and context
+- **Source detection** – Shows file:line for React components (dev mode with TanStack Devtools)
 - **Programmatic access** – Callback prop for direct integration with tools
 - **Dark/light mode** – Matches your preference or set manually
 - **Zero dependencies** – Pure CSS animations, no runtime libraries
@@ -47,6 +48,7 @@ The toolbar appears in the bottom-right corner. Click to activate, then click an
 | `onAnnotationsClear` | `(annotations: Annotation[]) => void` | - | Called when all annotations are cleared |
 | `onCopy` | `(markdown: string) => void` | - | Callback with markdown output when copy is clicked |
 | `copyToClipboard` | `boolean` | `true` | Set to false to prevent writing to clipboard |
+| `sourceAttribute` | `string` | `"data-tsd-source"` | Data attribute to read source file path from |
 
 ### Programmatic Integration
 
@@ -102,6 +104,10 @@ type Annotation = {
   accessibility?: string;
   isMultiSelect?: boolean;
   isFixed?: boolean;
+
+  // Source location (dev mode only)
+  sourceFile?: string;           // e.g., "src/components/Button.tsx:42"
+  sourceComponent?: string;      // Component name if available
 };
 ```
 
diff --git a/_package-export/src/components/page-toolbar-css/index.tsx b/_package-export/src/components/page-toolbar-css/index.tsx
index b42c53c..7ded40b 100644
--- a/_package-export/src/components/page-toolbar-css/index.tsx
+++ b/_package-export/src/components/page-toolbar-css/index.tsx
@@ -51,6 +51,11 @@ import {
   saveAnnotations,
   getStorageKey,
 } from "../../utils/storage";
+import {
+  getSourceLocation,
+  formatSourceLocation,
+  DEFAULT_SOURCE_ATTRIBUTE,
+} from "../../utils/source-location";
 
 import type { Annotation } from "../../types";
 import styles from "./styles.module.scss";
@@ -179,6 +184,13 @@ function generateOutput(
       if (a.isMultiSelect && a.fullPath) {
         output += `*Forensic data shown for first element of selection*\n`;
       }
+      if (a.sourceFile) {
+        output += `**Source:** ${a.sourceFile}`;
+        if (a.sourceComponent) {
+          output += ` (component: ${a.sourceComponent})`;
+        }
+        output += `\n`;
+      }
       if (a.fullPath) {
         output += `**Full DOM Path:** ${a.fullPath}\n`;
       }
@@ -208,6 +220,13 @@ function generateOutput(
     } else {
       // Standard and detailed modes
       output += `### ${i + 1}. ${a.element}\n`;
+      if (a.sourceFile) {
+        output += `**Source:** ${a.sourceFile}`;
+        if (a.sourceComponent) {
+          output += ` (${a.sourceComponent})`;
+        }
+        output += `\n`;
+      }
       output += `**Location:** ${a.elementPath}\n`;
 
       if (detailLevel === "detailed") {
@@ -261,6 +280,8 @@ export type PageFeedbackToolbarCSSProps = {
   onCopy?: (markdown: string) => void;
   /** Whether to copy to clipboard when the copy button is clicked. Defaults to true. */
   copyToClipboard?: boolean;
+  /** Data attribute name to read source location from. Defaults to "data-tsd-source" (TanStack Devtools). */
+  sourceAttribute?: string;
 };
 
 /** Alias for PageFeedbackToolbarCSSProps */
@@ -280,6 +301,7 @@ export function PageFeedbackToolbarCSS({
   onAnnotationsClear,
   onCopy,
   copyToClipboard = true,
+  sourceAttribute = DEFAULT_SOURCE_ATTRIBUTE,
 }: PageFeedbackToolbarCSSProps = {}) {
   const [isActive, setIsActive] = useState(false);
   const [annotations, setAnnotations] = useState<Annotation[]>([]);
@@ -307,6 +329,8 @@ export function PageFeedbackToolbarCSS({
     computedStyles?: string;
     computedStylesObj?: Record<string, string>;
     nearbyElements?: string;
+    sourceFile?: string;
+    sourceComponent?: string;
   } | null>(null);
   const [copied, setCopied] = useState(false);
   const [cleared, setCleared] = useState(false);
@@ -499,6 +523,7 @@ export function PageFeedbackToolbarCSS({
 
           const rect = element.getBoundingClientRect();
           const { name, path } = identifyElement(element);
+          const sourceResult = getSourceLocation(element, sourceAttribute);
 
           const newAnnotation: Annotation = {
             id: `demo-${Date.now()}-${index}`,
@@ -517,6 +542,11 @@ export function PageFeedbackToolbarCSS({
             },
             nearbyText: getNearbyText(element),
             cssClasses: getElementClasses(element),
+            sourceFile:
+              sourceResult.found && sourceResult.source
+                ? formatSourceLocation(sourceResult.source, "path")
+                : undefined,
+            sourceComponent: sourceResult.source?.componentName,
           };
 
           setAnnotations((prev) => [...prev, newAnnotation]);
@@ -764,6 +794,14 @@ export function PageFeedbackToolbarCSS({
       const computedStylesObj = getDetailedComputedStyles(elementUnder);
       const computedStylesStr = getForensicComputedStyles(elementUnder);
 
+      // Capture source location for React components
+      const sourceResult = getSourceLocation(elementUnder, sourceAttribute);
+      const sourceFile =
+        sourceResult.found && sourceResult.source
+          ? formatSourceLocation(sourceResult.source, "path")
+          : undefined;
+      const sourceComponent = sourceResult.source?.componentName;
+
       setPendingAnnotation({
         x,
         y,
@@ -785,6 +823,8 @@ export function PageFeedbackToolbarCSS({
         computedStyles: computedStylesStr,
         computedStylesObj,
         nearbyElements: getNearbyElements(elementUnder),
+        sourceFile,
+        sourceComponent,
       });
       setHoverInfo(null);
     };
@@ -1163,6 +1203,14 @@ export function PageFeedbackToolbarCSS({
             getDetailedComputedStyles(firstElement);
           const firstElementComputedStylesStr = getForensicComputedStyles(firstElement);
 
+          // Capture source location from first element
+          const sourceResult = getSourceLocation(firstElement, sourceAttribute);
+          const sourceFile =
+            sourceResult.found && sourceResult.source
+              ? formatSourceLocation(sourceResult.source, "path")
+              : undefined;
+          const sourceComponent = sourceResult.source?.componentName;
+
           setPendingAnnotation({
             x,
             y,
@@ -1184,6 +1232,8 @@ export function PageFeedbackToolbarCSS({
             nearbyElements: getNearbyElements(firstElement),
             cssClasses: getElementClasses(firstElement),
             nearbyText: getNearbyText(firstElement),
+            sourceFile,
+            sourceComponent,
           });
         } else {
           // No elements selected, but allow annotation on empty area
@@ -1249,6 +1299,8 @@ export function PageFeedbackToolbarCSS({
         accessibility: pendingAnnotation.accessibility,
         computedStyles: pendingAnnotation.computedStyles,
         nearbyElements: pendingAnnotation.nearbyElements,
+        sourceFile: pendingAnnotation.sourceFile,
+        sourceComponent: pendingAnnotation.sourceComponent,
       };
 
       setAnnotations((prev) => [...prev, newAnnotation]);
diff --git a/_package-export/src/types.ts b/_package-export/src/types.ts
index 042b617..59a598e 100644
--- a/_package-export/src/types.ts
+++ b/_package-export/src/types.ts
@@ -20,6 +20,10 @@ export type Annotation = {
   accessibility?: string;
   isMultiSelect?: boolean; // true if created via drag selection
   isFixed?: boolean; // true if element has fixed/sticky positioning (marker stays fixed)
+  /** Source file path with line number (dev mode only). e.g., "src/components/Button.tsx:42" */
+  sourceFile?: string;
+  /** React component name. e.g., "Button" */
+  sourceComponent?: string;
 };
 
 // TODO: Add configuration types when abstracting config
diff --git a/_package-export/src/utils/source-location.ts b/_package-export/src/utils/source-location.ts
index f2c9ff7..85d57d8 100644
--- a/_package-export/src/utils/source-location.ts
+++ b/_package-export/src/utils/source-location.ts
@@ -375,25 +375,52 @@ function findDebugSourceReact19(
 }
 
 /**
- * Gets the source file location for a DOM element in a React application
+ * Default data attribute for source location detection.
+ * TanStack Devtools uses "data-tsd-source" by default.
+ */
+export const DEFAULT_SOURCE_ATTRIBUTE = "data-tsd-source";
+
+/**
+ * Gets the source file location for a DOM element in a React application.
  *
  * This function attempts to extract the source file path and line number
  * where a React component is defined. This only works in development mode
  * as production builds strip debug information.
  *
  * @param element - DOM element to get source location for
+ * @param sourceAttribute - Data attribute to check for source info (default: "data-tsd-source")
  * @returns SourceLocationResult with location info or reason for failure
- *
- * @example
- * ```ts
- * const result = getSourceLocation(element);
- * if (result.found && result.source) {
- *   console.log(`${result.source.fileName}:${result.source.lineNumber}`);
- *   // Output: "/src/components/Button.tsx:42"
- * }
- * ```
  */
-export function getSourceLocation(element: HTMLElement): SourceLocationResult {
+export function getSourceLocation(
+  element: HTMLElement,
+  sourceAttribute: string = DEFAULT_SOURCE_ATTRIBUTE
+): SourceLocationResult {
+  // First, check for source attribute on DOM elements (e.g., data-tsd-source from TanStack Devtools)
+  // This can be customized via the sourceAttribute parameter
+  let current: HTMLElement | null = element;
+  while (current) {
+    const sourceValue = current.getAttribute(sourceAttribute);
+    if (sourceValue) {
+      // Format: "/src/components/Button.tsx:42:5" or "src/components/Button.tsx:42"
+      const match = sourceValue.match(/^(.+):(\d+)(?::(\d+))?$/);
+      if (match) {
+        const [, fileName, lineStr, colStr] = match;
+        return {
+          found: true,
+          source: {
+            fileName: fileName,
+            lineNumber: parseInt(lineStr, 10),
+            columnNumber: colStr ? parseInt(colStr, 10) : undefined,
+            componentName: undefined,
+          },
+          isReactApp: true,
+          isProduction: false,
+        };
+      }
+    }
+    current = current.parentElement;
+  }
+
   // Detect React environment
   const reactInfo = detectReactApp();