A small macOS utility

Fillet

Choose the right app at the moment you open a file. Fillet sits between Finder and your Markdown or JSON editor, showing a quiet picker instead of sending every file to the same default application.

Built for Markdown and JSON files on macOS 13 or later.
Download Fillet on the Mac App Store
Fillet showing a centered picker to open File.md in BBEdit, Code, TextEdit, or Typora
Fillet appears between the file and the final application, then gets out of the way.
Purpose

Pick the app that should open a file before it opens.

File types

Markdown, .markdown, and JSON files.

Privacy

Local-only behavior with no tracking or collected data.

What it does

A deliberate pause before macOS chooses for you.

Some files do not have a single obvious home. A Markdown file might belong in a notes app, a code editor, a writing tool, or a previewer. A JSON file might need inspection, editing, validation, or quick reference. Fillet gives those moments a small, centered chooser so the right application is a click away.

  • I

    Confirm the file

    See the file name and detected file type before anything opens, so you know exactly what is about to move.

  • II

    Choose from compatible apps

    Pick from macOS suggestions or your saved app list for that file type, without changing your mind permanently.

  • III

    Keep preferences per type

    Configure different choices for Markdown and JSON, then let Fillet remember the short list you actually use.

How to use it

Set Fillet once, then choose naturally from Finder.

01

Install Fillet

Download Fillet from the Mac App Store so macOS can offer it as a file-opening option.

02

Associate a file type

In Finder, select a Markdown or JSON file, open Get Info, choose Fillet under Open with, and apply it to that type.

03

Open a file

Double-click the file. Fillet appears with the file details and the available applications.

04

Pick or configure

Click an app to open the file there, or use Settings to add and remove saved choices for the current file type.

FAQ

Basic questions before using Fillet.

Fillet is intentionally small: it does not edit your files, sync them, or replace your tools. It helps you choose the right tool at the right moment.

What file types does Fillet support?

Fillet currently declares support for Markdown files, including .md and .markdown, plus JSON files.

Does Fillet become the editor?

No. Fillet is a chooser. It confirms the file and file type, then opens the file in the application you select.

How do I cancel without opening the file?

Press Esc or click the close button in the picker. Fillet closes and leaves the file untouched.

Can I set different app choices for different file types?

Yes. Fillet saves application choices per detected macOS file type, so Markdown and JSON can each have their own shortlist.

Does Fillet send my files anywhere?

No. The supplied app materials describe Fillet as local-only, with no tracking, collected data, tracking domains, or networked file handling.

Works with Actium

Annotation-aware opening for Actium workflows.

Fillet can work alongside Actium to recognise files with annotations and make Actium part of the opening decision. Instead of treating every Markdown or JSON file the same way, Fillet can surface Actium when the file carries context that belongs there.

  • Detect annotations

    When a file includes Actium-readable annotations, Fillet can identify that extra context before the file is opened.

  • Open directly in Actium

    Actium can be offered as an optional destination, letting annotated files move straight into the application that understands them.