Fix Run-On Sentences on Mac — Clean Up Your Writing in One Keystroke

Run-on sentences are the silent saboteurs of professional writing. They pile clause on top of clause until the reader loses track of the point entirely. You know the feeling — you reread a paragraph you just wrote and realize it's three thoughts fused into one breathless block.

If you want to fix run-on sentences without memorizing grammar rules or switching to a browser-based tool, WunderType gives you a faster path. It's a macOS menu bar app that uses AI-powered Custom Prompts to transform your text system-wide. Select the offending text, press a keyboard shortcut, and get back clean, properly structured sentences in place.

How to Fix Run-On Sentences with One Shortcut

WunderType works through Custom Prompts — reusable text actions, each with its own instruction and keyboard shortcut. The Sentence Refiner prompt reads your selected text, identifies where one thought ends and another begins, and rewrites the passage with correct punctuation and sentence boundaries. It works in Mail, Notes, Pages, Google Docs, Slack, and every other app on your Mac.

No copying text to a website. No pasting into a grammar checker. Select, press ⌥⇧⌘R, done.

See the Difference: Run-On Sentences vs. Properly Structured Text

Here's a paragraph that collapses multiple ideas into run-on sentences:

Before

The marketing team really needed to finalize the campaign brief, which was a bit of a mess to be honest. We had a lot of ideas floating around and the CEO wanted it done by Friday.

Select it, press ⌥⇧⌘R, and WunderType delivers tightened, well-structured prose:

After

The marketing team needed to finalize the campaign brief, which was disorganized. Many ideas were circulating, and the CEO's Friday deadline added urgency.

The transformation addresses several problems at once. Filler phrases like "really," "a bit of," and "to be honest" are stripped away. The loose comma splice is restructured so each sentence carries a single, clear thought. Vague language — "a lot of ideas floating around" — becomes precise: "Many ideas were circulating." The buried deadline detail is surfaced as its own grammatical unit, giving it the emphasis it deserves.

What Are the 5 Rules to Fix a Run-On Sentence?

Five reliable methods exist for fixing run-on sentences:

1. Period and capital letter — split the run-on into two independent sentences.
2. Semicolon — join closely related independent clauses when a full stop feels too abrupt.
3. Comma plus coordinating conjunction — connect clauses with a comma followed by and, but, or, nor, for, so, or yet.
4. Subordinating conjunction — make one clause dependent using because, although, when, or while.
5. Restructure entirely — rewrite the sentence so the ideas flow naturally without a mechanical fix.

WunderType's Sentence Refiner applies these rules contextually. It reads the meaning, decides which technique fits best, and rewrites accordingly — the kind of contextual judgment that separates it from grammar checkers that flag problems without fixing them well.

Set Up Your Sentence Refiner Prompt

1. Click the WunderType icon in your Mac's menu bar and open Custom Prompts
2. Create a new prompt named "Sentence Refiner" with an instruction like: Rewrite the selected text to fix run-on sentences. Break fused sentences into properly punctuated independent clauses. Remove filler words and tighten phrasing. Preserve the original meaning and tone. Output only the rewritten text.
3. Assign ⌥⇧⌘R as the keyboard shortcut — it now works in every app on your Mac

Beyond Run-Ons: Build a Complete Editing Toolkit

Run-on sentences are one category of writing problem. You can create additional Custom Prompts for other common issues:

• Sentence Refiner — fixes run-on sentences and comma splices into clean, structured prose
• Passive Voice Fixer — rewrites passive constructions into active, direct sentences
• Conciseness Editor — trims wordy phrases and redundancies without changing meaning
• Tone Adjuster — shifts casual drafts to formal register or vice versa

Each prompt gets its own keyboard shortcut. You build a personal editing suite that works everywhere on your Mac.

Your Writing, Your Mac, Your Privacy

WunderType connects to OpenAI or runs entirely offline through Ollama. With a local model, your documents and drafts never leave your Mac — no cloud processing, no third-party access to sensitive writing.

Download WunderType from the Mac App Store and stop letting run-on sentences undermine your writing.