A fast, tree-based viewer and editor for JSON files on Windows, inspired by Microsoft's
XML Notepad.
Built with C# / .NET 9 WinForms. No third-party packages.
Editing a large JSON file in a text editor means counting brackets and hunting for commas. JsonNotepad shows the document the way XML Notepad shows XML: a tree of names on the left and values on the right, with in-place editing, undo, and drag-and-drop restructuring. It stays responsive on files of hundreds of megabytes.
Viewing
- Two-column tree: names on the left, values on the right, with type badges, dotted tree lines and a draggable divider
- Virtualized rendering: millions of values scroll smoothly
- Text View: syntax-highlighted, pretty-printed text, virtualized for very large documents. Double-click a line to jump to its node in the tree
- Status bar with the JSONPath of the selection, type and size, plus encoding, line endings and indentation
- Light and dark themes (Options ▸ Theme)
Editing
- In-place editing of names and values
- Enter edits, Esc cancels, Ctrl+Enter adds a line break inside a string
- Numbers and booleans are validated as you type
- Insert ▸ Object / Array / String / Number / Boolean / Null ▸ Before / After / Child
- Change To: convert between types while keeping content (stringify and parse embedded JSON, object ⇄ array)
- Nudge Up/Down/Left/Right (Ctrl+Shift+arrows) and drag and drop (Ctrl to copy)
- Cut / Copy / Paste of subtrees as JSON text, including
"key": valuefragments - Duplicate, Sort Properties (optionally recursive), Edit as JSON (Ctrl+E)
- Unlimited-feeling undo/redo with compound steps (Replace All is one undo)
Finding and navigating
- Find / Replace (Ctrl+F / Ctrl+H): match case, whole word, regex, names and/or values
- Type-to-find in the tree, Go to Path (Ctrl+G), Copy Path (Ctrl+Shift+C)
Validating
- JSON Schema validation (drafts 4–2020-12 core vocabulary, local
$ref), runs in the background while you edit - Uses Tools ▸ Assign Schema, or a root
"$schema"pointing to a local file - Duplicate-key warnings
- Error list with click-to-navigate and F4 for the next error
Files
- Detects encoding (UTF-8/16/32, with or without BOM), indentation and line endings, and preserves them on save
- Output Format: Preserve / Indented / Compact (minified)
- Accepts comments and trailing commas (JSONC); both are configurable
- Crash-safe atomic saves, reload prompt when the file changes on disk, recent files, a location bar, drag files onto the window
- Statistics: counts per type, depth, largest containers and most frequent keys
| Option | How |
|---|---|
| Microsoft Store | coming soon |
| Installer | JsonNotepad-setup.exe (needs the .NET 9 Desktop Runtime) or JsonNotepad-setup-standalone.exe (includes .NET) |
| Portable | JsonNotepad-portable.zip, unzip and run (needs the .NET 9 Desktop Runtime) |
| All releases | GitHub Releases |
| Build from source | Requires the .NET 9 SDK |
git clone https://github.com/ismailian/JsonNotepad.git
cd JsonNotepad
dotnet build -c Release
dotnet run --project src/JsonNotepad.App -c Release -- samples/bookstore.jsonsamples/bookstore.json references bookstore.schema.json through $schema, so it opens with live validation errors you can try fixing.
dotnet run --project tests/JsonNotepad.Core.Tests -c Release # all tests
dotnet run --project tests/JsonNotepad.Core.Tests -c Release -- --exclude-category perf
dotnet run --project tests/JsonNotepad.Core.Tests -c Release -- Undo # filter by name| Script | Purpose |
|---|---|
build/build.ps1 |
Restore, build and test |
build/package-msix.ps1 -Bundle |
x64 + arm64 .msixbundle for the Store |
build/package-msix.ps1 -CreateDevCertificate |
Signed package for sideloading |
build/package-inno.ps1 |
Classic setup.exe (requires Inno Setup); -FrameworkDependent for the small variant |
build/package-release.ps1 |
Stage all GitHub release assets (stable names) + checksums + release notes |
build/package-site.ps1 |
Copy the small downloads into site/downloads for Cloudflare Pages |
build/version.ps1 minor |
Bump the version |
build/generate-icons.ps1 |
Regenerate the icon and Store assets |
| Action | Keys |
|---|---|
| Edit value / rename | Enter / F2 |
| Insert sibling / child | Ctrl+Enter / Ctrl+Shift+Enter |
| Nudge node | Ctrl+Shift+↑ ↓ ← → |
| Expand / collapse | → / ←, Num + / Num −, Num * (subtree) |
| Switch name/value column | Tab |
| Tree / Text / Error list | Ctrl+1 / Ctrl+2 / Ctrl+3 |
| Validate / next error | F5 / F4 |
| Find / next / previous | Ctrl+F / F3 / Shift+F3 |
| All shortcuts | F1 |
JsonNotepad.App (WinForms shell: MainForm, dialogs, settings, ActionRegistry)
│
├── JsonNotepad.Controls (owner-drawn, virtualized: JsonTreeView, JsonTextView, ErrorListView, themes)
│
└── JsonNotepad.Core (net9.0, no UI: model, streaming parser, writer, undo/redo,
JSONPath, find/replace, JSON Schema, background services)
Design patterns: Command + Composite (undo), Facade (NodeEditor, DocumentSession), Observer (model events), Builder (parser), Flyweight (name table), Strategy (find, conversions) and snapshot-based background processing. Read more:
| Document | Contents |
|---|---|
| docs/architecture.md | Layers, types, threading model, patterns |
| docs/xmlnotepad-analysis.md | What we learned from XML Notepad's source and how each idea was adapted |
| docs/performance.md | Large-file techniques and measurements |
| docs/packaging.md | Versioning, MSIX, Microsoft Store, Inno Setup, release checklist |
Issues and pull requests are welcome. Please read CLAUDE.md; it doubles as the contributor guide for conventions (no NuGet packages, Core stays UI-free, every edit goes through a command, background work uses snapshots). Run the test suite before submitting.
JsonNotepad's design is modeled on XML Notepad by Microsoft (MIT License). No XML Notepad code is included; see the analysis for what was learned from it.