diff --git a/changelog.md b/changelog.md
index 6d98a7d..a4c2f05 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## 2024-08-24 - 1.2.0 - feat(assertions)
+Add custom fail and success messages for assertions
+
+- Implemented withFailMessage method in Assertion class to customize fail messages
+- Implemented withSuccessMessage method in Assertion class to customize success messages
+- Enhanced error messages to use custom fail messages when provided
+
 ## 2024-08-17 - 1.1.0 - feat(assertion)
 Add toBeDefined assertion method
 
diff --git a/ts/00_commitinfo_data.ts b/ts/00_commitinfo_data.ts
index 0c72446..58eaff2 100644
--- a/ts/00_commitinfo_data.ts
+++ b/ts/00_commitinfo_data.ts
@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartexpect',
-  version: '1.1.0',
+  version: '1.2.0',
   description: 'A testing library to manage expectations in code, offering both synchronous and asynchronous assertion methods.'
 }
diff --git a/ts/index.ts b/ts/index.ts
index 4fba5a5..4abc376 100644
--- a/ts/index.ts
+++ b/ts/index.ts
@@ -1,5 +1,3 @@
-import * as plugins from './smartexpect.plugins.js';
-
 import { Assertion } from './smartexpect.classes.assertion.js';
 
 export const expect = (baseArg: any) => {
@@ -11,3 +9,4 @@ export const expectAsync = (baseArg: any) => {
   const assertion = new Assertion(baseArg, 'async');
   return assertion;
 };
+
diff --git a/ts/smartexpect.classes.assertion.ts b/ts/smartexpect.classes.assertion.ts
index 92beff3..9a5a3d4 100644
--- a/ts/smartexpect.classes.assertion.ts
+++ b/ts/smartexpect.classes.assertion.ts
@@ -31,6 +31,18 @@ export class Assertion {
     return this;
   }
 
+  private failMessage: string;
+  public withFailMessage(failMessageArg: string) {
+    this.failMessage = failMessageArg;
+    return this;
+  }
+
+  private successMessage: string;
+  public withSuccessMessage(successMessageArg: string) {
+    this.successMessage = successMessageArg;
+    return this;
+  }
+
   private runCheck(checkFunction: () => any) {
     const runDirectOrNegated = (checkFunction: () => any) => {
       if (!this.notSetting) {
@@ -43,7 +55,7 @@ export class Assertion {
           isOk = true;
         }
         if (!isOk) {
-          throw new Error('Negated assertion is not ok!');
+          throw new Error(this.failMessage || 'Negated assertion is not ok!');
         }
       }
     };
@@ -78,7 +90,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (this.getObjectToTestReference() === undefined) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not defined`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not defined`
         );
       }
     });
@@ -91,7 +103,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (typeof this.getObjectToTestReference() !== 'string') {
         throw new Error(
-          `Assertion failed: ${this.baseReference} with drill down ${
+          this.failMessage || `Assertion failed: ${this.baseReference} with drill down ${
             this.propertyDrillDown
           } is not of type string, but typeof ${typeof this.baseReference}`
         );
@@ -103,7 +115,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (typeof this.getObjectToTestReference() !== 'number') {
         throw new Error(
-          `Assertion failed: ${this.baseReference} with drill down ${
+          this.failMessage || `Assertion failed: ${this.baseReference} with drill down ${
             this.propertyDrillDown
           } is not of type string, but typeof ${typeof this.baseReference}`
         );
@@ -115,7 +127,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (typeof this.getObjectToTestReference() !== 'boolean') {
         throw new Error(
-          `Assertion failed: ${this.baseReference} with drill down ${
+          this.failMessage || `Assertion failed: ${this.baseReference} with drill down ${
             this.propertyDrillDown
           } is not of type string, but typeof ${typeof this.baseReference}`
         );
@@ -128,7 +140,7 @@ export class Assertion {
       const result = plugins.fastDeepEqual(this.getObjectToTestReference(), comparisonObject);
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not equal ${comparisonObject}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not equal ${comparisonObject}`
         );
       }
     });
@@ -139,7 +151,7 @@ export class Assertion {
       const result = comparisonObject.test(this.getObjectToTestReference());
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not equal ${comparisonObject}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not equal ${comparisonObject}`
         );
       }
     });
@@ -152,7 +164,7 @@ export class Assertion {
         this.getObjectToTestReference() === true;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not true or not of type boolean`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not true or not of type boolean`
         );
       }
     });
@@ -165,7 +177,7 @@ export class Assertion {
         this.getObjectToTestReference() === false;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not false or not of type boolean`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not false or not of type boolean`
         );
       }
     });
@@ -176,7 +188,7 @@ export class Assertion {
       const result = this.getObjectToTestReference() instanceof classArg;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not an instance of ${classArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not an instance of ${classArg}`
         );
       }
     });
@@ -187,13 +199,13 @@ export class Assertion {
       const result = !!this.getObjectToTestReference()[propertyArg];
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not have property ${propertyArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not have property ${propertyArg}`
         );
       }
       if (equalsArg) {
         if (result !== equalsArg) {
           throw new Error(
-            `${this.baseReference} with drill down ${this.propertyDrillDown} does have property ${propertyArg}, but it does not equal ${equalsArg}`
+            this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does have property ${propertyArg}, but it does not equal ${equalsArg}`
           );
         }
       }
@@ -213,7 +225,7 @@ export class Assertion {
         }
 
         if (!obj || !(property in obj)) {
-          throw new Error(`Missing property at path "${currentPath}" in ${this.baseReference}`);
+          throw new Error(this.failMessage || `Missing property at path "${currentPath}" in ${this.baseReference}`);
         }
         obj = obj[property];
       }
@@ -225,7 +237,7 @@ export class Assertion {
       const result = this.getObjectToTestReference() > numberArg;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not greater than ${numberArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not greater than ${numberArg}`
         );
       }
     });
@@ -236,7 +248,7 @@ export class Assertion {
       const result = this.getObjectToTestReference() < numberArg;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not less than ${numberArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not less than ${numberArg}`
         );
       }
     });
@@ -247,7 +259,7 @@ export class Assertion {
       const result = this.getObjectToTestReference() === null;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not null`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not null`
         );
       }
     });
@@ -258,7 +270,7 @@ export class Assertion {
       const result = this.getObjectToTestReference() === undefined;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not undefined`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not undefined`
         );
       }
     });
@@ -270,7 +282,7 @@ export class Assertion {
         this.getObjectToTestReference() === null || this.getObjectToTestReference() === undefined;
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not null or undefined`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not null or undefined`
         );
       }
     });
@@ -285,7 +297,7 @@ export class Assertion {
         this.getObjectToTestReference().includes(itemArg);
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not contain ${itemArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not contain ${itemArg}`
         );
       }
     });
@@ -295,7 +307,7 @@ export class Assertion {
     return this.runCheck(() => {
       const arrayRef = this.getObjectToTestReference();
       if (!Array.isArray(arrayRef) || arrayRef.length !== 0) {
-        throw new Error(`Expected ${this.baseReference} to be an empty array, but it was not.`);
+        throw new Error(this.failMessage || `Expected ${this.baseReference} to be an empty array, but it was not.`);
       }
     });
   }
@@ -304,13 +316,13 @@ export class Assertion {
     return this.runCheck(() => {
       const arrayRef = this.getObjectToTestReference();
       if (!Array.isArray(arrayRef)) {
-        throw new Error(`Expected ${this.baseReference} to be an array.`);
+        throw new Error(this.failMessage || `Expected ${this.baseReference} to be an array.`);
       }
 
       for (const value of values) {
         if (!arrayRef.includes(value)) {
           throw new Error(
-            `Expected ${this.baseReference} to include value "${value}", but it did not.`
+            this.failMessage || `Expected ${this.baseReference} to include value "${value}", but it did not.`
           );
         }
       }
@@ -321,12 +333,12 @@ export class Assertion {
     return this.runCheck(() => {
       const arrayRef = this.getObjectToTestReference();
       if (!Array.isArray(arrayRef)) {
-        throw new Error(`Expected ${this.baseReference} to be an array.`);
+        throw new Error(this.failMessage || `Expected ${this.baseReference} to be an array.`);
       }
 
       if (arrayRef.includes(value)) {
         throw new Error(
-          `Expected ${this.baseReference} to exclude value "${value}", but it included it.`
+          this.failMessage || `Expected ${this.baseReference} to exclude value "${value}", but it included it.`
         );
       }
     });
@@ -338,7 +350,7 @@ export class Assertion {
       const result = typeof testObject === 'string' && testObject.startsWith(itemArg);
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not contain ${itemArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not contain ${itemArg}`
         );
       }
     });
@@ -350,7 +362,7 @@ export class Assertion {
       const result = typeof testObject === 'string' && testObject.endsWith(itemArg);
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not contain ${itemArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not contain ${itemArg}`
         );
       }
     });
@@ -363,7 +375,7 @@ export class Assertion {
       const result = values.includes(this.getObjectToTestReference());
       if (!result) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not one of ${values}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not one of ${values}`
         );
       }
     });
@@ -374,7 +386,7 @@ export class Assertion {
       const obj = this.getObjectToTestReference();
       if (typeof obj.length !== 'number' || obj.length !== length) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not have a length of ${length}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not have a length of ${length}`
         );
       }
     });
@@ -385,7 +397,7 @@ export class Assertion {
       const difference = Math.abs(this.getObjectToTestReference() - value);
       if (difference > Math.pow(10, -precision) / 2) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not close to ${value} up to ${precision} decimal places`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not close to ${value} up to ${precision} decimal places`
         );
       }
     });
@@ -400,7 +412,7 @@ export class Assertion {
         thrown = true;
         if (expectedError && !(e instanceof expectedError)) {
           throw new Error(
-            `Expected function to throw ${expectedError.name}, but it threw ${e.name}`
+            this.failMessage || `Expected function to throw ${expectedError.name}, but it threw ${e.name}`
           );
         }
       }
@@ -414,7 +426,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (!this.getObjectToTestReference()) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not truthy`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not truthy`
         );
       }
     });
@@ -424,7 +436,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (this.getObjectToTestReference()) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not falsy`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not falsy`
         );
       }
     });
@@ -434,7 +446,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (this.getObjectToTestReference() <= numberArg) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not greater than or equal to ${numberArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not greater than or equal to ${numberArg}`
         );
       }
     });
@@ -455,7 +467,7 @@ export class Assertion {
       const partialMatch = plugins.fastDeepEqual(this.getObjectToTestReference(), objectArg); // Note: Implement a deep comparison function or use one from a library
       if (!partialMatch) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not match the object ${objectArg}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not match the object ${objectArg}`
         );
       }
     });
@@ -477,7 +489,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (!Array.isArray(this.getObjectToTestReference())) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not an array`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not an array`
         );
       }
     });
@@ -487,7 +499,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (!this.getObjectToTestReference().includes(substring)) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not include the substring ${substring}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not include the substring ${substring}`
         );
       }
     });
@@ -498,7 +510,7 @@ export class Assertion {
       const obj = this.getObjectToTestReference();
       if (typeof obj.length !== 'number' || obj.length <= length) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not have a length greater than ${length}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not have a length greater than ${length}`
         );
       }
     });
@@ -509,7 +521,7 @@ export class Assertion {
       const obj = this.getObjectToTestReference();
       if (typeof obj.length !== 'number' || obj.length >= length) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} does not have a length less than ${length}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} does not have a length less than ${length}`
         );
       }
     });
@@ -519,7 +531,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (!(this.getObjectToTestReference() instanceof Date)) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not a date`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not a date`
         );
       }
     });
@@ -529,7 +541,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (!(this.getObjectToTestReference() < date)) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not before ${date}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not before ${date}`
         );
       }
     });
@@ -539,7 +551,7 @@ export class Assertion {
     return this.runCheck(() => {
       if (!(this.getObjectToTestReference() > date)) {
         throw new Error(
-          `${this.baseReference} with drill down ${this.propertyDrillDown} is not after ${date}`
+          this.failMessage || `${this.baseReference} with drill down ${this.propertyDrillDown} is not after ${date}`
         );
       }
     });
@@ -548,7 +560,7 @@ export class Assertion {
   public customAssertion(assertionFunction: (value: any) => boolean, errorMessage: string) {
     return this.runCheck(() => {
       if (!assertionFunction(this.getObjectToTestReference())) {
-        throw new Error(errorMessage);
+        throw new Error(this.failMessage || errorMessage);
       }
     });
   }