diff --git a/packages/bruno-cli/src/runner/run-single-request.js b/packages/bruno-cli/src/runner/run-single-request.js
index 0fdda11ec..0479ad951 100644
--- a/packages/bruno-cli/src/runner/run-single-request.js
+++ b/packages/bruno-cli/src/runner/run-single-request.js
@@ -16,13 +16,12 @@ const path = require('path');
 const { parseDataFromResponse } = require('../utils/common');
 const { getCookieStringForUrl, saveCookies } = require('../utils/cookies');
 const { createFormData } = require('../utils/form-data');
-const protocolRegex = /^([-+\w]{1,25})(:?\/\/|:)/;
 const { NtlmClient } = require('axios-ntlm');
 const { addDigestInterceptor, getHttpHttpsAgents, makeAxiosInstance: makeAxiosInstanceForOauth2, applyOAuth1ToRequest } = require('@usebruno/requests');
 const { getCACertificates, transformProxyConfig } = require('@usebruno/requests');
 const { getOAuth2Token, getFormattedOauth2Credentials } = require('../utils/oauth2');
 const tokenStore = require('../store/tokenStore');
-const { encodeUrl, buildFormUrlEncodedPayload, extractPromptVariables, isFormData, extractBoundaryFromContentType } = require('@usebruno/common').utils;
+const { encodeUrl, buildFormUrlEncodedPayload, extractPromptVariables, isFormData, extractBoundaryFromContentType, hasExplicitScheme } = require('@usebruno/common').utils;
 
 const onConsoleLog = (type, args) => {
   console[type](...args);
@@ -344,7 +343,7 @@ const runSingleRequest = async function (
       request.url = encodeUrl(request.url);
     }
 
-    if (!protocolRegex.test(request.url)) {
+    if (!hasExplicitScheme(request.url)) {
       request.url = `http://${request.url}`;
     }
 
diff --git a/packages/bruno-cli/tests/runner/response-fields.spec.js b/packages/bruno-cli/tests/runner/response-fields.spec.js
index f3314fdcf..a10a4408f 100644
--- a/packages/bruno-cli/tests/runner/response-fields.spec.js
+++ b/packages/bruno-cli/tests/runner/response-fields.spec.js
@@ -68,14 +68,18 @@ jest.mock('../../src/store/tokenStore', () => ({
 
 // Default: no prompt variables detected
 const mockExtractPromptVariables = jest.fn(() => []);
-jest.mock('@usebruno/common', () => ({
-  utils: {
-    encodeUrl: jest.fn((u) => u),
-    buildFormUrlEncodedPayload: jest.fn(),
-    extractPromptVariables: mockExtractPromptVariables,
-    isFormData: jest.fn(() => false)
-  }
-}));
+jest.mock('@usebruno/common', () => {
+  const ogUtils = jest.requireActual('@usebruno/common').utils;
+  return {
+    utils: {
+      encodeUrl: jest.fn((u) => u),
+      buildFormUrlEncodedPayload: jest.fn(),
+      extractPromptVariables: mockExtractPromptVariables,
+      isFormData: jest.fn(() => false),
+      hasExplicitScheme: ogUtils.hasExplicitScheme
+    }
+  };
+});
 
 const prepareRequest = require('../../src/runner/prepare-request');
 const { makeAxiosInstance } = require('../../src/utils/axios-instance');
diff --git a/packages/bruno-common/src/utils/index.ts b/packages/bruno-common/src/utils/index.ts
index 3c76116dd..7e481a6aa 100644
--- a/packages/bruno-common/src/utils/index.ts
+++ b/packages/bruno-common/src/utils/index.ts
@@ -1,4 +1,5 @@
 export {
+  hasExplicitScheme,
   encodeUrl,
   parseQueryParams,
   buildQueryString,
diff --git a/packages/bruno-common/src/utils/url/index.spec.ts b/packages/bruno-common/src/utils/url/index.spec.ts
index 178297b83..69e0b80d1 100644
--- a/packages/bruno-common/src/utils/url/index.spec.ts
+++ b/packages/bruno-common/src/utils/url/index.spec.ts
@@ -1,4 +1,4 @@
-import { encodeUrl, parseQueryParams, buildQueryString } from './index';
+import { encodeUrl, parseQueryParams, buildQueryString, hasExplicitScheme } from './index';
 
 describe('encodeUrl', () => {
   describe('basic functionality', () => {
@@ -260,3 +260,49 @@ describe('buildQueryString', () => {
     expect(result).toBe('seat=&table=2');
   });
 });
+
+describe('hasExplicitScheme', () => {
+  // should return false
+  const noScheme: [string, string][] = [
+    ['bare hostname', 'test-domain'],
+    ['localhost', 'localhost'],
+    ['localhost:port (key regression)', 'localhost:8080'],
+    ['localhost:port/path', 'localhost:8080/path'],
+    ['127.0.0.1:port', '127.0.0.1:3000'],
+    ['bare IP', '192.168.1.1'],
+    ['IP:port', '192.168.1.1:8080'],
+    ['hostname with path', 'example.com/api/v1']
+  ];
+
+  for (const [label, url] of noScheme) {
+    it(`false (no explicit scheme) — ${label}`, () => {
+      expect(hasExplicitScheme(url)).toBe(false);
+    });
+  }
+
+  // should return true
+  const withScheme: [string, string][] = [
+    ['http://', 'http://example.com'],
+    ['https://', 'https://example.com'],
+    ['ftp://', 'ftp://test-domain'],
+    ['ws://', 'ws://example.com/socket'],
+    ['wss://', 'wss://example.com/socket'],
+    ['custom scheme', 'myapp://deep-link']
+  ];
+
+  for (const [label, url] of withScheme) {
+    it(`true (has explicit scheme) — ${label}`, () => {
+      expect(hasExplicitScheme(url)).toBe(true);
+    });
+  }
+
+  it('{{baseUrl}}/api — no scheme injection for template variables', async () => {
+    const url = '{{baseUrl}}/api/v1';
+    expect(hasExplicitScheme(url)).toBe(false);
+  });
+
+  it('{{baseUrl}} alone — no scheme injection for template variables', async () => {
+    const url = '{{baseUrl}}';
+    expect(hasExplicitScheme(url)).toBe(false);
+  });
+});
diff --git a/packages/bruno-common/src/utils/url/index.ts b/packages/bruno-common/src/utils/url/index.ts
index 466dca59f..dae5e65cb 100644
--- a/packages/bruno-common/src/utils/url/index.ts
+++ b/packages/bruno-common/src/utils/url/index.ts
@@ -1,3 +1,45 @@
+/**
+ * Returns true when `url` already carries an explicit network scheme.
+ *
+ * Per the WHATWG URL Standard, all network-fetch schemes (http, https, ftp,
+ * ws, wss, file) require "://" — the authority component is mandatory.
+ * This means "localhost:8080" is NOT a scheme: the colon separates host from
+ * port, so callers should prepend "http://" to it.
+ *
+ * The scheme character set (ASCII alpha/digit/+/-/.) follows the WHATWG URL
+ * scheme-state parser, which accepts the same characters as all major browsers.
+ * @see https://url.spec.whatwg.org/#scheme-state
+ *
+ * @example
+ * hasExplicitScheme('https://example.com') // true
+ * hasExplicitScheme('ftp://files.example') // true
+ * hasExplicitScheme('localhost:8080')       // false — port colon, not scheme
+ * hasExplicitScheme('example.com/api')      // false — no scheme at all
+ */
+function hasExplicitScheme(url: string): boolean {
+  // All WHATWG network schemes require authority ("://").
+  const authorityStart = url.indexOf('://');
+  if (authorityStart < 1) return false;
+
+  const scheme = url.slice(0, authorityStart);
+
+  // WHATWG URL scheme-state: first character must be ASCII alpha.
+  const first = scheme[0];
+  const isAlpha = (c: string) => {
+    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
+  };
+
+  if (!isAlpha(first)) {
+    return false;
+  }
+
+  // Remaining characters must be ASCII alphanumeric, "+", "-", or ".".
+  const isSchemeChar = (c: string) => {
+    return isAlpha(c) || (c >= '0' && c <= '9') || c === '+' || c === '-' || c === '.';
+  };
+  return scheme.slice(1).split('').every(isSchemeChar);
+}
+
 interface QueryParam {
   name: string;
   value?: string;
@@ -97,6 +139,7 @@ const stripOrigin = (url: string): string => {
 };
 
 export {
+  hasExplicitScheme,
   encodeUrl,
   parseQueryParams,
   buildQueryString,
diff --git a/packages/bruno-electron/src/ipc/network/index.js b/packages/bruno-electron/src/ipc/network/index.js
index 1445a0979..73fbf34d1 100644
--- a/packages/bruno-electron/src/ipc/network/index.js
+++ b/packages/bruno-electron/src/ipc/network/index.js
@@ -10,7 +10,7 @@ const { ipcMain } = require('electron');
 const { each, get, extend, cloneDeep, merge } = require('lodash');
 const { NtlmClient } = require('axios-ntlm');
 const { VarsRuntime, AssertRuntime, ScriptRuntime, TestRuntime, formatErrorWithContextV2 } = require('@usebruno/js');
-const { encodeUrl } = require('@usebruno/common').utils;
+const { encodeUrl, hasExplicitScheme } = require('@usebruno/common').utils;
 const { extractPromptVariables } = require('@usebruno/common').utils;
 const { interpolateString } = require('./interpolate-string');
 const { resolveAwsV4Credentials, addAwsV4Interceptor } = require('./awsv4auth-helper');
@@ -108,9 +108,8 @@ const configureRequest = async (
   collectionPath,
   globalEnvironmentVariables
 ) => {
-  const protocolRegex = /^([-+\w]{1,25})(:?\/\/|:)/;
   const hasVariables = request.url.startsWith('{{');
-  if (!hasVariables && !protocolRegex.test(request.url)) {
+  if (!hasVariables && !hasExplicitScheme(request.url)) {
     request.url = `http://${request.url}`;
   }
 
diff --git a/packages/bruno-electron/tests/network/index.spec.js b/packages/bruno-electron/tests/network/index.spec.js
index 5fa443132..6df3dc876 100644
--- a/packages/bruno-electron/tests/network/index.spec.js
+++ b/packages/bruno-electron/tests/network/index.spec.js
@@ -1,15 +1,80 @@
 const { configureRequest } = require('../../src/ipc/network/index');
 
-describe('index: configureRequest', () => {
-  it('Should add \'http://\' to the URL if no protocol is specified', async () => {
-    const request = { method: 'GET', url: 'test-domain', body: {} };
+// Integration tests: full configureRequest (URL must survive cookie-jar parse)
+describe('index: configureRequest — URL normalization', () => {
+  it('prepends http:// to localhost:port', async () => {
+    const request = { method: 'GET', url: 'localhost:8080', body: {} };
     await configureRequest(null, {}, request, null, null, null, null);
-    expect(request.url).toEqual('http://test-domain');
+    expect(request.url).toEqual('http://localhost:8080');
   });
 
-  it('Should NOT add \'http://\' to the URL if a protocol is specified', async () => {
+  it('prepends http:// to localhost', async () => {
+    const request = { method: 'GET', url: 'localhost', body: {} };
+    await configureRequest(null, {}, request, null, null, null, null);
+    expect(request.url).toEqual('http://localhost');
+  });
+
+  it('prepends http:// to 127.0.0.1:port', async () => {
+    const request = { method: 'GET', url: '127.0.0.1:3000', body: {} };
+    await configureRequest(null, {}, request, null, null, null, null);
+    expect(request.url).toEqual('http://127.0.0.1:3000');
+  });
+
+  it('prepends http:// to example.com/api/v1', async () => {
+    const request = { method: 'GET', url: 'example.com/api/v1', body: {} };
+    await configureRequest(null, {}, request, null, null, null, null);
+    expect(request.url).toEqual('http://example.com/api/v1');
+  });
+
+  it('does not prepend http:// to http://example.com', async () => {
+    const request = { method: 'GET', url: 'http://example.com', body: {} };
+    await configureRequest(null, {}, request, null, null, null, null);
+    expect(request.url).toEqual('http://example.com');
+  });
+
+  it('does not prepend http:// to https://example.com', async () => {
+    const request = { method: 'GET', url: 'https://example.com', body: {} };
+    await configureRequest(null, {}, request, null, null, null, null);
+    expect(request.url).toEqual('https://example.com');
+  });
+
+  it('does not prepend http:// to ftp://test-domain', async () => {
     const request = { method: 'GET', url: 'ftp://test-domain', body: {} };
     await configureRequest(null, {}, request, null, null, null, null);
     expect(request.url).toEqual('ftp://test-domain');
   });
+
+  it('does not prepend http:// to ws://example.com/socket', async () => {
+    const request = { method: 'GET', url: 'ws://example.com/socket', body: {} };
+    await configureRequest(null, {}, request, null, null, null, null);
+    expect(request.url).toEqual('ws://example.com/socket');
+  });
+
+  describe('with variables in the url and no interpolation values', () => {
+    it('does not prepend http:// to {{baseUrl}}/api/v1 (template variable)', async () => {
+      const url = '{{baseUrl}}/api/v1';
+      const request = { method: 'GET', url, body: {} };
+      expect.assertions(2);
+      try {
+        await configureRequest(null, {}, request, null, null, null, null);
+      } catch (err) {
+        expect(err.message).toBe('Invalid URL');
+      } finally {
+        expect(request.url).toEqual(url);
+      }
+    });
+
+    it('does not prepend http:// to {{baseUrl}} alone (template variable)', async () => {
+      const url = '{{baseUrl}}';
+      const request = { method: 'GET', url, body: {} };
+      expect.assertions(2);
+      try {
+        await configureRequest(null, {}, request, null, null, null, null);
+      } catch (err) {
+        expect(err.message).toBe('Invalid URL');
+      } finally {
+        expect(request.url).toEqual(url);
+      }
+    });
+  });
 });
diff --git a/packages/bruno-tests/collection/url-serialization/scheme.bru b/packages/bruno-tests/collection/url-serialization/scheme.bru
new file mode 100644
index 000000000..6c3618d3b
--- /dev/null
+++ b/packages/bruno-tests/collection/url-serialization/scheme.bru
@@ -0,0 +1,16 @@
+meta {
+  name: scheme
+  type: http
+  seq: 1
+}
+
+get {
+  url: localhost:8081/ping
+  body: none
+  auth: none
+}
+
+assert {
+  res.status: eq 200
+  res.body: eq pong
+}