# Gander: Quick Look previews for Markdown, Mermaid, JSON and SQLite on Mac

> Gander is a Quick Look extension for macOS by 65FN LLC. Select a developer file in Finder and press Space to see a rich preview: Markdown (GitHub-flavoured, with Mermaid diagrams, math, footnotes, alerts and emoji), Mermaid files, JSON and JSON Lines, SQLite databases (read-only), .env files (values hidden until revealed), YAML, TOML, source code, archives, GZIP text, folders and MIDI. It also draws Finder thumbnails. Everything runs locally; no data is collected.

Gander turns the Quick Look preview in Finder into a real viewer for the files developers open every day: Markdown with Mermaid diagrams, JSON, SQLite, .env files and 30+ more types. No editor, no switching apps.

- **Name:** Gander (on the App Store: Gander: Quick Look Preview)
- **What it is:** A Quick Look preview and Finder thumbnail extension for macOS
- **Developer:** 65FN LLC
- **Requires:** macOS 15 or later
- **Where to get it:** Mac App Store, coming soon
- **Privacy:** Data Not Collected; no network access
- **Category:** Developer Tools
- **File types:** 40 file extensions, plus dotfiles, extensionless files and folders
- **Version:** 1.0

## See it in 29 seconds

Every preview in the video is a real render from Gander’s Quick Look extension.

Video: https://ganderfinder.com/video/gander-tour-en.mp4 (29 s, no narration)

What the video shows:

- 0:00 A Finder window shows a sample project called nimbus, and README.md is selected.
- 0:02 Space is pressed, and Quick Look opens README.md as rendered Markdown.
- 0:04 The README scrolls past a Mermaid flowchart, a table and a task list.
- 0:06 Mermaid files open as diagrams: a sequence diagram, a Gantt roadmap and a git graph.
- 0:10 nimbus.sqlite opens read-only: rows from two tables, then the Structure tab.
- 0:14 A JSON Lines log shows one record per line, and one record expands as formatted JSON.
- 0:18 A .env file opens with every value hidden, Show values reveals them, then they are hidden again.
- 0:22 YAML, TOML, Python and a ZIP archive preview in turn.
- 0:25 Closing title: “Press Space. Take a gander.”

## A viewer for each file in your project

Gander gives each kind of file a preview built for it. Previews follow your Mac’s light or dark appearance, and every image on this page is a real render from the app.

### Markdown, rendered the way GitHub shows it

README files open rendered, with the Raw source one click away. Everything in GitHub-flavoured Markdown works, plus the extras that usually need a browser.

- Tables, task lists, strikethrough and autolinks
- Math with `$…$` and `$$…$$`, and footnotes
- GitHub alerts: Note, Tip, Important, Warning and Caution
- `:emoji:` shortcodes, and `mermaid` code blocks drawn as diagrams

![README.md rendered: the Nimbus Weather API title, a Tip alert and a Mermaid flowchart of how a request flows.](https://ganderfinder.com/img/features/md-render-2x.webp)
![The same README scrolled to an Endpoints table and a Release checklist with ticked and unticked tasks.](https://ganderfinder.com/img/features/md-scroll-2x.webp)

### Mermaid diagrams without a browser

`.mmd` and `.mermaid` files open as diagrams, with the source on the next tab. Gander draws flowcharts, sequence, class, state and ER diagrams, XY charts, pie charts, mindmaps, timelines, Gantt charts, user journeys, git graphs, quadrant charts, C4 and requirement diagrams.

![roadmap.mmd as a Gantt chart: the Nimbus 3.0 roadmap with bars for radar tiles and heat index alerts.](https://ganderfinder.com/img/features/mmd-gantt-2x.webp)
![branches.mmd as a git graph with main and radar-v2 branches and a v2.4.0 tag.](https://ganderfinder.com/img/features/mmd-git-2x.webp)
![architecture.mmd as a sequence diagram: User, iOS App, Forecast API and Postgres exchanging requests.](https://ganderfinder.com/img/features/mmd-seq-2x.webp)

### JSON and JSON Lines you can actually read

JSON opens instantly, even large files, with Tree and Raw views. JSON Lines and NDJSON logs show one record per line. Click a line number to expand that record as indented JSON, in the file’s own key order, and click again to fold it.

![forecast.json in the Tree view: city, country and the current conditions as nested keys.](https://ganderfinder.com/img/features/json-tree-2x.webp)
![api-requests.jsonl with record 6 expanded as indented JSON, showing an upstream timeout error.](https://ganderfinder.com/img/features/jsonl-open-2x.webp)

### Look inside SQLite databases

`.sqlite`, `.sqlite3` and `.db` files open read-only, so the database is never modified and no journal files appear beside it. Structure lists every table’s columns, types, keys and indexes. Content shows the rows, table by table, up to the first 200 of each.

![nimbus.sqlite on the Structure tab: the api_keys and cities tables with column types, primary keys and NOT NULL flags.](https://ganderfinder.com/img/features/sqlite-structure-2x.webp)
![nimbus.sqlite on the Content tab: the cities table with 12 rows of names, countries, latitudes and longitudes.](https://ganderfinder.com/img/features/sqlite-content-2x.webp)

### Secrets stay hidden until you choose

Environment files open with every value masked. Keys stay visible, and likely secrets such as passwords, tokens, API keys and private keys are marked SECRET. Values appear only when you choose Show values, and copying from the hidden view never copies a real value.

![.env.production with Show values on: plain values such as the port and log level next to flagged secrets.](https://ganderfinder.com/img/features/env-shown-2x.webp)
![.env.production in the default Hidden view: every value masked, with keys like STRIPE_API_KEY marked SECRET.](https://ganderfinder.com/img/features/env-hidden-2x.webp)

### Config, code, archives and the rest

YAML, TOML, `.cfg` and `.config` files open as typed, colour-coded structures, and `package.json` gets an overview of its name, version, scripts and dependencies. Swift, Python, JavaScript and shell scripts are syntax-highlighted, and the line numbers stay out of anything you copy. ZIP, XIP, tar and `.tar.gz` archives list their contents without extracting, GZIP files show their text, and MIDI files play.

![forecast_service.py with Python syntax highlighting and numbered lines.](https://ganderfinder.com/img/features/code-py-2x.webp)
![package.json overview: the nimbus-dashboard name, version 2.4.0 and its scripts.](https://ganderfinder.com/img/features/pkg-2x.webp)
![nimbus-2.4.0.zip listing the files inside the archive.](https://ganderfinder.com/img/features/zip-2x.webp)

### Real thumbnails in Finder

In icon, gallery and column view, Finder shows a page of the file itself: rendered Markdown, coloured JSON, YAML and code, Mermaid sources and archive contents. Thumbnails of `.env` files show keys only, never values.

## Nothing leaves your Mac

Gander reads the file you’re previewing and nothing else. It has no account, no analytics and no networking code, and its extensions run in Apple’s App Sandbox without network access. The App Store privacy label is **Data Not Collected**.

- Runs 100% on your Mac
- No account, no subscription
- Nothing is uploaded

Read the privacy policy: https://ganderfinder.com/privacy

## Set up in under a minute

1. Install Gander from the Mac App Store.
2. Open Gander once. Its window shows whether Quick Look is using it, and lets you choose which file types and Markdown extras it handles.
3. In Finder, select a file and press Space.

Still seeing the standard preview? Turn on Gander in **System Settings › General › Login Items & Extensions › Quick Look**. The Gander window has a button that opens that page.

## Supported file types

Select any of these in Finder and press Space. The last column says whether Finder also shows a Gander thumbnail.

| Kind | Extensions | What you see | Finder thumbnail |
|---|---|---|---|
| Markdown | `.md`, `.markdown`, `.mdown`, `.markdn` | Rendered GitHub-flavoured Markdown with Mermaid, math, footnotes, alerts and emoji, plus the Raw source | Yes |
| Mermaid | `.mmd`, `.mermaid` | The diagram, plus the source | Yes |
| JSON | `.json` | Tree and Raw views, fast even for large files | Yes |
| JSON Lines | `.jsonl`, `.ndjson` | One record per line; click a line number to expand it | Yes |
| package.json | `package.json` | Name, version, scripts and dependencies | Yes |
| YAML | `.yaml`, `.yml` | A typed, colour-coded structure | Yes |
| TOML | `.toml` | A typed, colour-coded structure | Yes |
| Config files | `.cfg`, `.config` | A typed, colour-coded structure | Yes |
| SQLite | `.sqlite`, `.sqlite3`, `.db` | Read-only Structure and Content tabs, up to 200 rows per table | No |
| Environment files | `.env`, `.env.*`, `*.env` | Keys with values hidden until you choose Show values | Yes, keys only |
| Source code | `.swift`, `.py`, `.js`, `.mjs`, `.cjs`, `.sh`, `.bash`, `.zsh` | Swift, Python, JavaScript and shell with syntax highlighting and line numbers | Yes |
| Plain text | `.txt`, `.text`, `.ini`, dotfiles, files with no extension | The text, read safely; binary files are left to macOS | Yes |
| Archives | `.zip`, `.xip`, `.tar`, `.tgz`, `.tar.gz` | The list of files inside, without extracting | Yes, except XIP |
| GZIP | `.gz`, `.gzip` | The decompressed text, up to 32 KB | No |
| Folders | any folder | The list of items inside | No |
| MIDI | `.mid`, `.midi`, `.smf`, `.kar` | Play, pause and scrub | No |

## Questions and answers

### What is Gander?

Gander is a Quick Look extension for macOS, made by 65FN LLC. When you select a file in Finder and press Space, Gander draws a rich preview for developer files such as Markdown, Mermaid diagrams, JSON, SQLite databases and `.env` files. It also draws Finder thumbnails for most of them.

### Which Macs does Gander run on?

Any Mac with macOS 15 or later.

### Does Gander upload or collect my files?

No. Gander has no networking code and collects no data. Previews are drawn on your Mac, and the App Store privacy label is Data Not Collected.

### Does previewing an SQLite database change it?

No. Gander opens databases read-only and immutable, so it never writes to the file or creates `-wal`, `-shm` or journal files beside it. Rows that exist only in an uncommitted `-wal` file aren’t shown, and the preview says so.

### Will Gander show the secrets in my .env files?

Only when you ask. Every value is hidden when the preview opens; keys stay visible, and likely secrets are marked SECRET. Choose Show values to reveal them. Finder thumbnails of `.env` files show keys only.

### Can Gander draw Mermaid diagrams inside Markdown?

Yes. A fenced code block marked `mermaid` is drawn as a diagram inside the rendered page, and `.mmd` or `.mermaid` files open as diagrams on their own.

### I pressed Space and still see the standard preview. What now?

Open Gander once, then go to System Settings › General › Login Items & Extensions › Quick Look and make sure Gander is turned on. If another app previews the same file type, turn that one off. Then select the file in Finder and press Space again.

### Why don’t SQLite files get a Gander thumbnail?

macOS doesn’t let third-party thumbnail extensions handle SQLite files, so Finder keeps its own icon. Pressing Space still opens the full Gander preview.

### Can I turn some previews off?

Yes. The Gander window has a switch for each file category and for each Markdown extra: math, footnotes, GitHub alerts and emoji. Switch a category off and Gander stops handling that type.

### Why do images in my Markdown show as text?

Quick Look previews can’t load images, so Gander shows each image as a picture icon and its alt text.

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