Castl — Your 3D print model library for the Mac

Features

Know what you have. Find it when you need it.

Four things Castl does well — for STL, OBJ, and 3MF files, plus the zip archives they arrive in.

▦

See

A library you can browse, not a folder you have to remember.

✓Real rendered 3-D thumbnails, in a grid or a sortable list
✓Full 3-D viewer with a print-bed grid, wireframe & bounds overlays
✓Quick Look-style preview on the Space bar
✓Open side-by-side viewer windows to compare models

◍

Know

Every mesh analyzed once, at import — before it wastes filament.

✓Exact dimensions, triangle count, volume & surface area
✓Watertight, manifold, and degenerate-triangle checks
✓Problem models flagged automatically in their own scope
✓One-click handoff to PrusaSlicer, Bambu Studio, OrcaSlicer, or Cura

⌘

Organize

Collections for projects. Tags for everything else.

✓Designer, license, source link, and notes on every model
✓Bulk editing for cataloging a whole haul at once
✓Search that speaks 3-D printing: tag:calibration designer:"Jane"
✓Models findable in Spotlight — results open right in Castl

⟳

Automate

Point Castl at a folder and let your library file itself.

✓Watch folders auto-import new files — subfolders and zips included
✓Content fingerprinting catches exact duplicates, even renamed
✓Your call every time: skip, link to the original, or keep both
✓Missing files noticed and relinked, not silently forgotten

⧉

Duplicate Model

dragon_bust_final(2).stl is already in your library as dragon_bust_v3.

New file ~/Downloads/dragon_bust_final(2).stl

In library ~/Models/dragons/dragon_bust_v3.stl

Identical file content — SHA-256 9f31acc2e802f1d4…

SkipLink to ExistingKeep Both

Native · macOS 14+

Your files stay yours. All of them, once.

Castl fingerprints every file's content, so the same model can't sneak in twice — renamed, re-downloaded, or buried in a zip. And whatever it catalogs, it never rewrites.

✓Managed copies in Castl's library, or in-place indexing that leaves files exactly where they are
✓No repairs, no re-saves, no "optimizing" — deleting a model removes only the catalog entry
✓App Sandbox, no accounts, no telemetry — and a Liquid Glass icon on macOS 26 Tahoe
✓A bundled user guide in the Help menu, readable offline

The details

Requirements & privacy.

Requirements

macOS 14 (Sonoma) or later

Apple Silicon or Intel · STL, OBJ, 3MF & zip

Privacy

No data collected

No accounts, no network requests — your models and library stay on your Mac. Read the → Privacy policy

License

Buy once on the App Store

No account, no subscription, no telemetry

Every model you own.
One library.