diff --git a/package-lock.json b/package-lock.json
index fc665ff2..795b5656 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -28,6 +28,7 @@
         "grunt-contrib-watch": "^1.1.0",
         "grunt-string-replace": "^1.3.3",
         "jasmine": "^5.8.0",
+        "typescript": "^5.8.3",
         "underscore": "^1.13.7"
       }
     },
@@ -10399,6 +10400,20 @@
       "integrity": "sha512-/aCDEGatGvZ2BIk+HmLf4ifCJFwvKFNb9/JeZPMulfgFracn9QFcAf5GO8B/mweUjSoblS5In0cWhqpfs/5PQA==",
       "dev": true
     },
+    "node_modules/typescript": {
+      "version": "5.8.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.8.3.tgz",
+      "integrity": "sha512-p1diW6TqL9L07nNxvRMM7hMMw4c5XOo/1ibL4aAIGmSAt9slTE1Xgw5KWuof2uTOvCg9BY7ZRi+GaF+7sfgPeQ==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
+    },
     "node_modules/uglify-js": {
       "version": "3.17.4",
       "resolved": "https://registry.npmjs.org/uglify-js/-/uglify-js-3.17.4.tgz",
diff --git a/package.json b/package.json
index 62d75c08..f4f10836 100644
--- a/package.json
+++ b/package.json
@@ -37,11 +37,12 @@
     "grunt-contrib-watch": "^1.1.0",
     "grunt-string-replace": "^1.3.3",
     "jasmine": "^5.8.0",
+    "typescript": "^5.8.3",
     "underscore": "^1.13.7"
   },
   "scripts": {
     "test": "npm run jasmine && npm run wdio",
-    "jasmine": "jasmine --config=jasmine.json",
+    "jasmine": "jasmine --config=jasmine.json && jasmine tests/specs/typescript-definitions.js",
     "wdio": "cross-env node_modules/.bin/wdio wdio.conf.js"
   },
   "keywords": [
diff --git a/tests/specs/typescript-definitions.js b/tests/specs/typescript-definitions.js
new file mode 100644
index 00000000..a02beaeb
--- /dev/null
+++ b/tests/specs/typescript-definitions.js
@@ -0,0 +1,23 @@
+/* globals describe, it, expect */
+
+var { exec } = require('child_process');
+var path = require('path');
+
+describe("TypeScript Definitions", function() {
+  it("should compile without errors", function(done) {
+    var tsFile = path.join(__dirname, '../types-test.ts');
+    var cmd = 'npx tsc --noEmit ' + tsFile + ' --strict';
+    
+    exec(cmd, function(error, stdout, stderr) {
+      if (error) {
+        console.error('TypeScript compilation failed:', error);
+        console.error('stdout:', stdout);
+        console.error('stderr:', stderr);
+        expect(error).toBeNull();
+      } else {
+        console.log('TypeScript compilation succeeded');
+      }
+      done();
+    });
+  });
+});
diff --git a/tests/types-test.ts b/tests/types-test.ts
new file mode 100644
index 00000000..ca042fc7
--- /dev/null
+++ b/tests/types-test.ts
@@ -0,0 +1,92 @@
+import { RaygunPayload, RaygunStatic } from '../types/index';
+
+// Test RaygunPayload interface
+function testPayloadStructure(): void {
+    const payload: RaygunPayload = {
+        OccurredOn: new Date(),
+        Details: {
+            Error: {
+                ClassName: 'Error',
+                Message: 'Test error',
+                StackTrace: []
+            },
+            Environment: {
+                UtcOffset: 0,
+                "User-Language": 'en-US',
+                "Document-Mode": 11,
+                "Browser-Width": 1920,
+                "Browser-Height": 1080,
+                "Screen-Width": 1920,
+                "Screen-Height": 1080,
+                "Color-Depth": 24,
+                Browser: 'Chrome',
+                "Browser-Name": 'Chrome',
+                "Browser-Version": '120.0.0',
+                Platform: 'Linux'
+            },
+            Client: {
+                Name: 'raygun4js',
+                Version: '3.1.3'
+            },
+            UserCustomData: {},
+            Tags: [],
+            Request: {
+                Url: 'https://example.com',
+                QueryString: '',
+                Headers: {
+                    "User-Agent": 'Mozilla/5.0',
+                    Referer: 'https://example.com',
+                    Host: 'example.com'
+                }
+            },
+            Version: '1.0.0',
+            User: {
+                Identifier: 'test-user',
+                IsAnonymous: false,
+                Email: 'test@example.com',
+                FullName: 'Test User',
+                FirstName: 'Test',
+                UUID: 'test-uuid'
+            },
+            GroupingKey: 'test-group',
+            Breadcrumbs: [
+                {
+                    type: 'manual',
+                    message: 'Test breadcrumb',
+                    level: 'info',
+                    metadata: { test: true }
+                }
+            ]
+        }
+    };
+}
+
+// Test that onBeforeSend callback can access and modify breadcrumbs
+function testOnBeforeSendBreadcrumbAccess(): void {
+    // Mock Raygun instance
+    const raygun = {} as RaygunStatic;
+
+    // This should compile without TypeScript errors
+    raygun.onBeforeSend((payload: RaygunPayload) => {
+        // Access breadcrumbs
+        if (payload.Details.Breadcrumbs) {
+            // Filter out sensitive breadcrumbs
+            payload.Details.Breadcrumbs = payload.Details.Breadcrumbs.filter(breadcrumb => {
+                return breadcrumb.message !== 'sensitive-operation';
+            });
+
+            // Sanitize breadcrumb messages
+            payload.Details.Breadcrumbs = payload.Details.Breadcrumbs.map(breadcrumb => ({
+                ...breadcrumb,
+                message: breadcrumb.message?.replace(/password|secret|token/gi, '[REDACTED]')
+            }));
+        }
+
+        return payload;
+    });
+}
+
+export {
+    testPayloadStructure,
+    testOnBeforeSendBreadcrumbAccess,
+};
diff --git a/types/index.d.ts b/types/index.d.ts
index e292d340..57a76796 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -23,6 +23,13 @@ interface RaygunStackTrace {
     MethodName: string;
 }
 
+interface RaygunBreadcrumb {
+    type?: string;
+    message?: string;
+    level?: BreadcrumbLevel;
+    metadata?: any;
+}
+
 interface RaygunOptions {
     /**
      * Posts error payloads over HTTP. This allows IE8 to send JS errors.
@@ -171,6 +178,7 @@ interface RaygunPayload {
             UUID?: any;
         };
         GroupingKey?: string | undefined;
+        Breadcrumbs?: RaygunBreadcrumb[];
     };
 }
 
@@ -432,6 +440,6 @@ interface Window {
     Raygun: RaygunStatic;
 }
 
-export { BreadcrumbLevel, RaygunOptions, RaygunPayload, RaygunStackTrace, RaygunStatic, RaygunV2, RaygunV2UserDetails };
+export { BreadcrumbLevel, RaygunBreadcrumb, RaygunOptions, RaygunPayload, RaygunStackTrace, RaygunStatic, RaygunV2, RaygunV2UserDetails };
 
 export default rg4js;