added another blog post

Author: ozziest

docs/BlogIndex.vue

@@ -2,11 +2,17 @@
 const posts = [
   {
     time: "13 July, 2025",
+    title:
+      "How to Build a Custom Validation Rule in JavaScript with Robust Validator",
+    url: "/blog/2025-07-13-how-to-build-a-custom-validation-rule-in-javascript-with-robust-validator",
+  },
+  {
+    time: "12 July, 2025",
     title: "How to Validate Nested Objects in JavaScript with Robust Validator",
-    url: "/blog/2025-07-12-nested-object-validation",
+    url: "/blog/2025-07-12-how-to-validate-nested-objects-in-javascript-with-robust-validator",
   },
   {
-    time: "13 July, 2025",
+    time: "12 July, 2025",
     title: "What’s New in Robust Validator v3",
     url: "/blog/2025-07-13-whats-new-in-robust-validator-v3",
   },

…g/2025-07-12-nested-object-validation.md …s-in-javascript-with-robust-validator.mddocs/blog/2025-07-12-nested-object-validation.md renamed to docs/blog/2025-07-12-how-to-validate-nested-objects-in-javascript-with-robust-validator.md docs/blog/2025-07-12-nested-object-validation.md renamed to docs/blog/2025-07-12-how-to-validate-nested-objects-in-javascript-with-robust-validator.md

@@ -145,7 +145,5 @@ Give it a try and make your validation cleaner and more reliable.
 ## Related Links
 
 - [Getting Started](https://validator.axe-api.com/getting-started)
-
 - [All Validation Rules](https://validator.axe-api.com/rules)
-
 - [Customization](https://validator.axe-api.com/customization)

docs/blog/2025-07-13-how-to-build-a-custom-validation-rule-in-javascript-with-robust-validator.md

@@ -0,0 +1,143 @@
+---
+sidebar: false
+editLink: true
+outline: false
+prev: false
+next: false
+description: Learn how to create your own custom validation rules in JavaScript using Robust Validator. A simple step-by-step guide with examples.
+---
+
+# How to Build a Custom Validation Rule in JavaScript with Robust Validator
+
+## Intro
+
+Sometimes the built-in validation rules are not enough. You might need to check something unique to your app. For example, maybe a username must start with an uppercase letter. Or maybe a field needs to match a very specific format.
+
+Good news is that with [Robust Validator](https://validator.axe-api.com), you can easily create your own validation rules and use them just like the default ones.
+
+In this post, you’ll learn how to write a custom rule from scratch and plug it into your validation flow.
+
+## What We’ll Build
+
+Let’s build a custom rule called `startsWithUppercase`. It will check if a string starts with a capital letter.
+
+This rule is not included by default, but it’s easy to add your own.
+
+## Step 1: Define the Rule Function
+
+Your rule function is where you write the logic. It receives the value and returns true or false.
+
+```ts
+const ruleFunction = (value) => {
+  if (typeof value !== "string") return false;
+  return /^[A-Z]/.test(value);
+};
+```
+
+This checks if the first character of the value is an uppercase letter.
+
+## Step 2: Register the Rule
+
+Use the `register()` function to add your rule to the validator. You also provide a custom error message for each language.
+
+```ts
+import { register } from "robust-validator";
+
+register("startsWithUppercase", ruleFunction, {
+  en: "The field must start with an uppercase letter.",
+});
+```
+
+## Step 3: Write the Validation Schema
+
+Now you can use your custom rule in a string-based schema, just like a built-in rule.
+
+```ts
+import { validate } from "robust-validator";
+
+const data = {
+  name: "john",
+};
+
+const schema = {
+  name: "required|startsWithUppercase",
+};
+```
+
+## Step 4: Run the Validation
+
+The `validate()` function is asynchronous, so make sure to await it.
+
+```ts
+const result = await validate(data, schema);
+
+console.log(result);
+```
+
+## Example Output
+
+If the name does not start with a capital letter, you’ll get this:
+
+```json
+{
+  "isValid": false,
+  "isInvalid": true,
+  "fields": {
+    "name": false
+  },
+  "errors": {
+    "name": [
+      {
+        "rule": "startsWithUppercase",
+        "message": "The field must start with an uppercase letter."
+      }
+    ]
+  }
+}
+```
+
+## Use Case: Exists Rule for Database
+
+You can also create rules that connect to external sources like a database. For example:
+
+```ts
+const existsRule = async (value: any, tableName: string) => {
+  const fakeDatabase = {
+    users: ["user@example.com", "admin@example.com"],
+  };
+
+  return fakeDatabase[tableName]?.includes(value);
+};
+
+register("exists", existsRule, {
+  en: "The record doesn't exist in {0}.",
+});
+
+const result = await validate(
+  { email: "notfound@example.com" },
+  { email: "required|exists:users" },
+);
+```
+
+This checks if the email exists in a fake "users" table.
+
+## Why Custom Rules Are Useful
+
+Custom rules help when:
+
+- You need app-specific logic
+- You want to reuse complex checks
+- You need to integrate with your database or API
+- Built-in rules are not enough for your case
+
+## Wrap-Up
+
+Robust Validator makes it super easy to create and use your own validation rules. All you need is a rule function, a call to `register()`, and a schema. You can also customize the error messages for any language you need.
+
+Try creating your own rule today and make your validation logic match your app’s exact needs.
+
+## Related Links
+
+- [Getting Started](https://validator.axe-api.com/getting-started)
+- [All Validation Rules](https://validator.axe-api.com/rules)
+- [Customization](https://validator.axe-api.com/customization)