100% Local · Light Postman Client · Fast HTTP requests
API Tester
Lightweight, in-browser REST client. Test HTTP endpoints with custom parameters, headers, bodies, and auth configurations securely.
Encrypted browser sandbox Zero data logging
ParameterValue
Enter a URL and click Send to make a request
Browser Sandbox (CORS Enforced)CORS Active
Browser blocks cross-origin requests without CORS headers. Run the Desktop Agent to bypass.
Desktop Companion Agent
Offline
How It Works
Bypass browser CORS, mixed-content blocks, and localhost restrictions. The agent runs locally on your machine with 100% privacy — no cloud proxies.
Step 1
Download
Click the download button above
Windows .exe · macOS .command · Linux .deb/.rpm
Or use the raw Python script (zero pip deps)
Step 2
Run
Double-click the downloaded file
A console opens on 127.0.0.1:45456
Keep it open while testing
Step 3
Allow Loopback
Click the tune (sliders) or 🔒 lock icon left of URL
Toggle "Apps on device" → Allow
Refresh the page (one-time Chrome permission)
Step 4
Test
Agent auto-connects instantly
Green "Agent Active" badge appears
All requests bypass CORS natively
Zero CORS · Full localhost access
Loopback Only
127.0.0.1 — no external access
Zero Cloud Relay
Direct machine-to-server
Zero Dependencies
Python std library only
1-Click Shutdown
Stop anytime from web UI
Verify agent is running: Run in any terminal
curl http://127.0.0.1:45456/health
Developer Reference
Free Online REST API Client with Multi-Tab Sessions
A lightweight, free, and secure browser-based Postman alternative. Test GET, POST, PUT, and DELETE requests across up to 6 independent tab sessions — complete with auth, parameters, body editors, and instant response inspection. No install. No login.
Multi-Tab Sessions
Up to 6 isolated request tabs — each with its own URL, auth, body, and response.
100% Local
All HTTP calls execute in your browser. Zero server relay. Credentials stay private.
Full Auth Support
Basic Auth (with password reveal), Bearer, JWT, and API Key in header or query.
Rich Response View
Status badges, response time, body size, raw headers, and formatted JSON output.
Multi-Tab API Session Manager
New
The tab bar at the top of the tool works exactly like browser tabs — each pill is an entirely separate request context. Open a GET in one tab, a POST in another, and a Bearer-authenticated DELETE in a third, all visible side-by-side without any state bleeding between them.
Add Tab ( + )
Click the + button on the right of the tab bar to open a fresh, blank request context. Up to 6 tabs allowed.
Switch Tabs
Click any tab pill to instantly switch. Your previous URL, method, body, auth, and response are all preserved.
Method Badge
Each tab pill shows a colour-coded method badge (GET green, POST indigo, PUT amber, DELETE red) for at-a-glance identification.
Live Spinner
A spinning indicator appears on the tab pill while its request is in-flight, so you always know which tab is loading.
Reset Current Tab
The ↺ reset button clears only the active tab's state — URL, params, body, auth, and response — leaving all other tabs untouched.
6-Tab Hard Cap
To maintain performance, the + button is disabled once you reach 6 tabs. Close an existing tab to open a new one.
Why Use an Online HTTP / API Client?
API Clients are foundational utilities during backend and frontend integrations. Instead of writing curl commands or installing desktop software, this visual tool lets you structure endpoints, configure auth, and inspect responses inside a clean browser interface — instantly accessible from any device.
Our tool is a lightweight Postman alternative that loads in seconds with no registration, no installation, and no cloud sync. It is ideal for verifying public APIs, validating webhook destinations, checking JSON schema outputs, and running multiple endpoint tests in parallel using the multi-tab session feature.
HTTP Request Anatomy
Every API request contains key building blocks that dictate how servers process payloads:
Core Request Architecture
METHOD → GET, POST, PUT, DELETE
URL → https://api.domain.com/v1/users
PARAMS → ?page=1&limit=20 (auto-appended)
HEADERS → Authorization: Bearer <token>
Content-Type: application/json
BODY → { "username": "dev_coder" }
RESPONSE → STATUS (200 OK, 404 Not Found…)
HEADERS (Cache-Control, ETag…)
BODY (JSON, HTML, plain text)
Supported Authentication Methods
Configure per-tab authentication without affecting other open sessions. Each auth type is isolated to the tab it was set in.
Auth Type
How It Works
Sent As
Extra Feature
Basic Auth
Base64-encodes username:password automatically
Authorization: Basic …
👁 Password visibility toggle
Bearer Token
Prefixes your raw token string
Authorization: Bearer …
—
JWT
Sends JSON Web Token as a Bearer
Authorization: Bearer …
—
API Key
Custom key name + value
Header or Query param
Configurable location
None
No auth header added
—
—
Basic Auth — Password Visibility Toggle
The password field in the Basic Auth panel includes an eye (👁) icon button. Clicking it reveals the password in plain text so you can verify the exact credentials before sending. The toggle is per-tab — different tabs can independently show or hide their passwords. Credentials are encoded only in your browser and never stored externally.
Method Examples
HTTP request templates — inspect & copy
Select any method below to view standard configurations. Open each in a different tab to test them in parallel.
Request URL
GET https://jsonplaceholder.typicode.com/todos/1
Headers: Accept: application/json
Body Payload
None
💡 Retrieves a representation of a resource. Ideal for fetching user data, configuration, or item lists. Open a new tab and paste this URL to test simultaneously.
CLI & Browser Synergy
Bidirectional cURL Integration: Import & Export in 1-Click
Seamlessly bridge terminal commands with visual debugging. Convert raw terminal cURL snippets into rich, editable UI tabs, and export active sessions back to standardized cURL scripts in seconds.
RFC 7230 Compliant
Zero Dependencies
Smart cURL ImportCLI → UI
Paste from DevTools, Postman, Swagger, or terminal docs
Click Import cURL in the top header. Our client-side parser parses complex command strings into their constituent parts:
HTTP Method: Auto-detects -X POST, -X PUT, -X DELETE, -X PATCH (defaults to GET)
URL & Parameters: Splits query strings directly into the interactive key-value Params table
Right-click any failed network call in Chrome, Firefox, or Safari DevTools, click Copy as cURL, and paste it straight into JsonifyTools to inspect and replay.
Team Reproductions & Jira
Export exact request reproductions into Slack, Jira tickets, or pull requests so backend teammates can instantly test and verify the same bug report.
CI/CD & Automation
Prototype requests visually with parameter auto-completion, then export the verified cURL command directly into GitHub Actions or deployment scripts.
Common HTTP Methods Comparison
Understanding standard HTTP semantics is essential when designing REST integrations. Use a separate tab for each method to test your full CRUD API surface in one view.
Method
Idempotent
Has Request Body
Purpose
GET
Yes
No
Fetch details of a resource without side effects.
POST
No
Yes
Create a new resource on the server.
PUT
Yes
Yes
Replace or update a complete resource model.
DELETE
Yes
No
Permanently remove a resource by ID.
HTTP Status Guide
HTTP Status Codes Quick Reference
When you dispatch requests using our online API tester, the response panel displays the exact status code returned by your server:
200 OK
Standard response for successful GET, PUT, or POST requests.
201 Created
The request succeeded and a new resource was created (common for POST).
204 No Content
Request processed successfully, but no content body is returned (common for DELETE).
400 Bad Request
Server cannot process request due to malformed JSON body or invalid syntax.
A fresh tab opens automatically. Click '+' to add up to 5 more tabs for parallel endpoint testing across GET, POST, PUT, and DELETE.
2
Enter URL & Method
Type your endpoint URL and choose the HTTP method. Paste a URL with a query string and the tool will auto-extract parameters into the Params tab.
3
Configure Auth
Go to the Auth tab. Choose Basic Auth (use the eye icon to verify your password), Bearer Token, JWT, or API Key with header/query placement.
4
Set Headers & Body
Add custom request headers in the Headers tab. Switch to Body to set a JSON or plain-text payload for POST and PUT requests.
5
Send & Inspect
Hit 'Send'. The response panel shows status code, time in ms, body size, formatted JSON or raw text output, and all response headers.
6
Reset or Switch Tab
Hit ↺ Reset to clear the current tab for a fresh call. Switch to another tab to compare responses without losing your work.
API Testing Scenarios
JSON Response Validation — verify schemas match expected shapes
Auth Token Verification — test header authentication across different tab configs
Speed Benchmarking — compare roundtrip latency across multiple endpoints in parallel
CORS Checking — detect cross-origin policy issues in browser sandboxes
Parameter Debugging — test complex query strings and body parsers side by side
Credential Auditing — use the Basic Auth password toggle to verify credentials before sending
Key Tool Features
Multi-tab sessions — up to 6 fully isolated request contexts
Per-tab reset button — clears only the active tab, other tabs untouched
Chrome-style tab bar with method badges, live spinner, and close buttons
GET, POST, PUT, and DELETE HTTP methods
URL parameter auto-extraction into editable key-value rows
Basic Auth with password visibility toggle (👁 icon)
Bearer token, JWT, and API Key (header or query) authentication
JSON and plain-text request body editors
Timing metrics — response time in milliseconds, body size in bytes
Full response parser — status code, formatted body, and all headers
100% client-side sandbox — credentials never leave your browser
No install, no registration, no cloud sync required
Zero-CORS Companion Service · Localhost & Intranet
Desktop Companion Agent: Bypass Browser CORS & Test Any API Natively
Web browsers enforce strict sandbox rules that block cross-origin calls, localhost endpoints, and private networks. The JsonifyTools Companion Agent is a lightweight, local helper service that dispatches requests natively on your operating system with zero restrictions.
Port 45456 Active Bridge
The Problem: Browser Sandboxing & CORS
✕Strict CORS Block: Modern browsers refuse cross-origin HTTP calls unless target servers send exact Access-Control-Allow-Origin headers.
✕Blocked Localhost & Docker: HTTPS web apps cannot call http://localhost:3000 or local microservices due to browser Mixed Content & Private Network Access blocks.
✕Stripped Request Headers: Browsers silently drop or forbid critical headers like User-Agent, Cookie, Host, and Origin.
✕Self-Signed SSL Failures: Local staging microservices running self-signed development certificates trigger fatal SSL exceptions in browser engines.
The Solution: Desktop Companion Agent
✓Zero CORS Restrictions: Requests are executed natively outside the browser runtime, returning complete responses with zero cross-origin errors.
✓Full Localhost & LAN Access: Effortlessly test APIs running on 127.0.0.1, localhost:8080, Docker containers, and corporate intranet subnets.
✓100% Header Fidelity: Transmits custom User-Agent, session cookies, and authentication headers exactly as you defined them with zero stripping.
✓Permissive SSL Testing: Includes built-in support for dev certificates, self-signed microservices, and internal staging environments.
Why It's 100% Secure, Easy & Transparent
Local Loopback Only
The agent listens exclusively on 127.0.0.1:45456. It is completely inaccessible from the outside internet or local Wi-Fi.
Zero Cloud Relaying
Your API requests travel directly from your computer to your target server. No payload, auth header, or response body ever touches an external third-party proxy.
Pure Standard Library
Built with Python's standard library with zero external pip packages. The complete source code is open and inspectable in under 300 lines of clean code.
Instant One-Click Control
Start the agent whenever you need native testing, and cleanly terminate it at any time by clicking the Stop Agent button in the UI or pressing Ctrl+C.
Available Native Packages for All Platforms
Free download · No telemetry · No sign-up
Windows (.exe)
8.5 MB
Single standalone executable. Double-click to run. Requires zero installation and no Python setup. Runs a clean local console on port 45456.
Standalone Executable
macOS (.command)
1.0 KB
Double-click command script that leverages macOS's built-in python3, or run via our 1-liner curl install command.
Native Python3 Script
Linux (.deb / .rpm)
~3.5 KB
Official packages for Ubuntu/Debian (.deb · 3.9 KB) and Fedora/RHEL (.rpm · 3.5 KB) for native system package managers.
Debian & Red Hat Packages
Universal Python
10 KB
Run anywhere with python jsonifytools_agent.py. Compatible with Python 3.8+ on Windows, macOS, Linux, FreeBSD, and WSL.
Cross-Platform Script
How The Agent Architecture Connects
Zero-CORS Request Lifecycle
Step 1 · Client
JsonifyTools Web UI
You configure tabs, auth, headers, and body payloads in the browser.
⇄↓127.0.0.1:45456⇄
Local Loopback
Step 2 · Bridge
Desktop Companion Agent
Dispatches HTTP calls natively via OS sockets outside browser CORS sandboxes.
⇄↓Native Socket⇄
Zero CORS Block
Step 3 · Target
Target API Endpoint
localhost:3000, Docker containers, private LANs, or external cloud APIs.
Security and Privacy Guarantee
Unlike desktop tools that aggregate histories and sync credentials to centralized cloud services, this web client is completely local and private. Every fetch runs sandboxed in your browser's native Fetch API. No request data, headers, tokens, or body payloads ever touch our servers.
Multi-tab session data lives entirely in React component state for the lifetime of the page. Refreshing or closing the tab clears everything instantly. API keys set in one tab are isolated from all other tabs by design — no accidental credential bleed between sessions.
💡 Tip: Ensure your target API is served over HTTPS to protect transmission across local networks. Basic Auth credentials are Base64-encoded in-browser — always use HTTPS in production.
Frequently Asked Questions
Everything about multi-tab sessions, authentication, CORS, reset, and privacy.
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