diff --git a/src/App/Decorator/Middleware.ts b/src/App/Decorator/Middleware.ts
index af9fe90..0044812 100644
--- a/src/App/Decorator/Middleware.ts
+++ b/src/App/Decorator/Middleware.ts
@@ -32,7 +32,7 @@ export function validator<T extends {}>(method: keyof ValidationTargets, data: Z
         const targetFunc = descriptor.value as Function;
         const funcValidator = honoValidator(method, (val, c) => {
             const parsed = z.object(data).safeParse(val);
-            if (!parsed.success) return onValidateError(c, data);
+            if (!parsed.success) return onValidateError(c, parsed.error.issues);
             return parsed.data;
         });
         reflectingMetadata(targetFunc, funcValidator);
diff --git a/src/App/Error/ErrorBuilder.ts b/src/App/Error/ErrorBuilder.ts
new file mode 100644
index 0000000..2f1bb42
--- /dev/null
+++ b/src/App/Error/ErrorBuilder.ts
@@ -0,0 +1,91 @@
+import type { StatusCode } from "hono/utils/http-status";
+
+export type IErrorBuilder<T> = {
+    title: string;
+    detail: string;
+    type: string;
+    instance?: string;
+    kind?: T;
+};
+
+/**
+ * Error builder for Agni based on IETF Error Convention.
+ *
+ * @see - RFC 9457
+ */
+export default class ErrorBuilder<T extends {}> implements IErrorBuilder<T> {
+    public type: string = "about:blank";
+    public instance?: string;
+    public kind?: T;
+
+    public constructor(public title: string, public detail: string) {}
+
+    private setProps<P extends keyof this>(prop: P, val: this[P]): this {
+        this[prop] = val;
+        return this;
+    }
+
+    /**
+     * Set additional fields on error query
+     */
+    public setKind<D extends T>(data: D): ErrorBuilder<D> {
+        return this.setProps("kind", data) as unknown as ErrorBuilder<D>;
+    }
+
+    /**
+     * Set instance or path where error raised on error query
+     */
+    public setInstance(instance: string): this {
+        return this.setProps("instance", instance);
+    }
+
+    /**
+     * Set code error type on error query
+     */
+    public setMDNCodeType(code: StatusCode): this {
+        return this.setProps("type", `https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/${code}`);
+    }
+
+    /**
+     * Set type of error URI on error query
+     */
+    public setType(type: string): this {
+        return this.setProps("type", type);
+    }
+
+    /**
+     * Set the title on error query
+     */
+    public setTitle(title: string): this {
+        return this.setProps("title", title);
+    }
+
+    /**
+     * Set the detail on error query
+     */
+    public setDetail(detail: string): this {
+        return this.setProps("detail", detail);
+    }
+
+    /**
+     * Generate the error query
+     */
+    public build(): IErrorBuilder<T> {
+        const data: IErrorBuilder<T> = {
+            type: this.type,
+            title: this.title,
+            detail: this.detail
+        };
+
+        if (this.instance !== undefined) {
+            data.instance = this.instance;
+        }
+
+        if (this.kind !== undefined) {
+            data.kind = this.kind;
+        }
+
+        return data;
+    }
+}
+
diff --git a/src/Function/OnError.ts b/src/Function/OnError.ts
index ebbb2eb..7e4b63e 100644
--- a/src/Function/OnError.ts
+++ b/src/Function/OnError.ts
@@ -1,45 +1,32 @@
 import { randomUUID } from "node:crypto";
 import type { Context, Env } from "hono";
-import type { HTTPException } from "hono/http-exception";
+import { HTTPException } from "hono/http-exception";
 import type { StatusCode } from "hono/utils/http-status";
+import ErrorBuilder from "App/Error/ErrorBuilder.js";
 import isJson from "App/Function/IsJson.js";
 import Logger from "Logger.js";
 
-type ErrorRecord = {
-    message: string;
-    errMessage?: string;
-    uuidErr?: string;
-};
-
 export default function onError(err: Error, c: Context<Env, any, any>): Response {
-    const errResponse: ErrorRecord = {
-        message: ""
-    };
-    errResponse.message = "Something happened, but don't worry maybe it's you or our developer.";
-    errResponse.errMessage = err.message;
+    const builder = new ErrorBuilder(
+        "Fatal error from server.", err.message
+    );
     let code: StatusCode = 500;
 
     // Expecting this is HTTPError
-    if (Object.keys(err).includes("status")) {
-        const newErr = err as HTTPException;
-        code = newErr.status;
-
-        errResponse.message = newErr.message;
-        delete errResponse.errMessage;
+    if (err instanceof HTTPException) {
+        code = err.status;
+        builder.setTitle("HTTP Error has thrown.");
     }
 
-    // If fatal error
     if (code === 500) {
-        errResponse.uuidErr = randomUUID();
-        Logger.child({ uuid: errResponse.uuidErr }).error(err, "Fatal error on server");
+        const uuid = randomUUID();
+        builder.setKind({ uuid });
+        Logger.child({ uuid }).error(err, "Fatal error on server");
     }
 
     const jsonMethod = isJson(c.req.header());
-    if (jsonMethod) return c.json(errResponse, code);
+    if (jsonMethod) return c.json(builder.build(), code);
 
     // You can improve on this side, this is just example.
-    let msgText = errResponse.message;
-    if (errResponse.errMessage !== undefined) msgText += `\n${errResponse.errMessage}`;
-    if (errResponse.uuidErr !== undefined) msgText += `\nUUID Code: ${errResponse.uuidErr}`;
-    return c.text(msgText, code);
+    return c.text(`Error: ${builder.title}\n${builder.detail}`, code);
 }
diff --git a/src/Function/OnNotFound.ts b/src/Function/OnNotFound.ts
index f60e75e..1810395 100644
--- a/src/Function/OnNotFound.ts
+++ b/src/Function/OnNotFound.ts
@@ -1,12 +1,16 @@
 import type { Context } from "hono";
+import ErrorBuilder from "App/Error/ErrorBuilder.js";
 import isJson from "App/Function/IsJson.js";
 
 export function onNotFound(c: Context<any, any, any>): Response {
-    const message = "Path not found.";
     const code = 404;
+    const builder = new ErrorBuilder("Not found.", "Path or route not found.");
+    builder
+        .setInstance(c.req.path)
+        .setMDNCodeType(code);
 
     const jsonMethod = isJson(c.req.header());
-    if (jsonMethod) return c.json({ message }, code);
+    if (jsonMethod) return c.json(builder.build(), code);
 
-    return c.text(message, code);
+    return c.text(builder.detail, code);
 }
diff --git a/src/Function/OnValidateError.ts b/src/Function/OnValidateError.ts
index 46d8c6d..1bb49fd 100644
--- a/src/Function/OnValidateError.ts
+++ b/src/Function/OnValidateError.ts
@@ -1,14 +1,18 @@
 import type { Context } from "hono";
 import type { ZodData } from "App/Decorator/Middleware.js";
+import ErrorBuilder from "App/Error/ErrorBuilder.js";
 import isJson from "App/Function/IsJson.js";
 
 export function onValidateError(c: Context<any, any, any>, data: ZodData<any>): Response {
-    const message = "Bad request performed.";
     const code = 400;
-    const propsOnServer = Object.keys(data);
+    const builder = new ErrorBuilder("Bad request.", "Bad request performed.");
+    builder
+        .setKind(data)
+        .setInstance(c.req.path)
+        .setMDNCodeType(code);
 
     const jsonMethod = isJson(c.req.header());
-    if (jsonMethod) return c.json({ message, propsOnServer }, code);
+    if (jsonMethod) return c.json(builder.build(), code);
 
-    return c.text(message, code);
+    return c.text(builder.detail, code);
 }