Web appActivePublished: March 14, 2026· Updated: June 20, 2026

JSON Lens

A fast, privacy-friendly JSON viewer and formatter that runs entirely in your browser.

Open toolSource code

Tech stack

AstroTypeScriptWeb Workers

What it does

JSON Lens pretty-prints, validates, and lets you explore large JSON documents without sending anything to a server. Everything happens locally in your browser.

Highlights

  • Private by design — your data never leaves the page.
  • Handles big files — parsing runs in a Web Worker so the UI stays responsive.
  • Collapsible tree + raw views — jump between a structured tree and formatted text.

Usage

Paste JSON, or drag a file onto the window:

{ "hello": "world", "items": [1, 2, 3] }

Use the tree on the left to collapse and expand nodes, and the toolbar to copy a minified or prettified version.

Status

Actively maintained and used daily.

Knowledge base

Guides and notes related to this entry.

3 articles

  • Knowledge base

    Opening large JSON safely

    Keep the UI responsive

    JSON Lens parses on a Web Worker. For files over a few MB:

    • Prefer drag-and-drop over pasting huge strings.
    • Collapse deep nodes before expanding siblings.
    • Use search instead of manually scanning.

    Stub copy for modal review.

  • Knowledge base

    Worker architecture overview

    Pipeline

    1. Main thread receives the file.
    2. Worker parses and builds a tree index.
    3. UI virtualizes rows so only visible nodes mount.

    No JSON leaves the browser. Replace this stub with diagrams later.

  • Knowledge base

    Keyboard shortcuts

    Navigation

    • j / k — move between nodes
    • Enter — expand or collapse
    • / — focus search
    • r — toggle raw vs tree

    Stub shortcuts list for the modal demo.

Tags:jsondeveloper-toolsprivacy