The short version is this: Grammarly is better for most people, and ProWritingAid is better specifically for long-form technical writing. But the gap is real, and which side of it you land on depends on what you actually write.
If you're producing API documentation, internal developer guides, README files, runbooks, or onboarding docs for other engineers, the two tools have different strengths. Picking the wrong one won't ruin your writing, but it will add friction to your workflow.
What Grammarly does well (and where it gets annoying for technical writers)
Grammarly is fast. That's the main thing. You open a doc, start typing, and suggestions appear in real time. The browser extension works inside Notion, Google Docs, Confluence, Linear, and pretty much everywhere else you write. For general editing, the experience is smooth.
The problem for technical content is that Grammarly has opinions. Strong ones. It really wants you to write in active voice. That sounds reasonable until you realize that a lot of technical documentation uses passive voice deliberately. "The function is called with two arguments" is actually clearer in many doc contexts than "you call the function with two arguments," and Grammarly will flag it every single time.
It also has trouble with technical vocabulary at first. Write something like "the endpoint returns a 404 if the resource doesn't exist" and it might want to change something. It gets better the more you train it with custom words, but that takes time.
Where Grammarly earns its money: catching real mistakes. Typos, wrong tense, a sentence that ran on way longer than it needed to. For a quick proofread before publishing or sending, it's genuinely useful and stays mostly out of the way.
What ProWritingAid handles better
ProWritingAid works differently. Instead of real-time suggestions on each sentence, you run full reports on your document. There's a Readability Report, a Consistency Report, a Sticky Sentences Report, and about twenty others. You don't run them all. You run the ones that matter for your use case.
For technical documentation, the Consistency Report is the one worth paying for on its own. It catches things like writing "API key" in some sections and "api-key" in others, or switching between "click" and "select" for the same action. Grammarly won't catch those. ProWritingAid will.
The style suggestions are also less opinionated. ProWritingAid shows you patterns in your writing without pushing you toward a specific voice. It's more "here's what I noticed" and less "here's how you should write."
The downside is that it's slower. The analysis takes a few seconds to run, and the interface is clunkier than Grammarly's. It doesn't work well as a real-time companion while you're drafting. It works better as a review tool: you finish a section, run a report, then go through the suggestions.
A practical comparison
Say you're writing a getting started guide for a developer tool. It's got numbered steps, code blocks, some notes about edge cases. As you type, Grammarly runs in the background and catches the typo in step 3 before you even finish the sentence. Useful, not intrusive.
Now say you've written a 3,000-word internal specification. You want to check that your terminology is consistent throughout, spot paragraphs that are too dense to read clearly, and make sure you haven't written the same thing three different ways. ProWritingAid is better here. The full-document reports give you something Grammarly's sentence-by-sentence approach doesn't.
Pricing
Grammarly Premium runs about $12 to $15 per month on an annual plan. The free version covers spelling and basic grammar.
ProWritingAid Premium is around $10 per month annually. The lifetime plan is $399, which a lot of writers buy once and stop thinking about. If you're going to use it for years, the lifetime deal makes the math easy.
Which one should you actually get?
If you're writing short-form content, emails, quick internal docs, or you just want something running in the background while you work: Grammarly. The browser extension is excellent and the real-time feedback works well for everyday writing.
If you write long technical documents, developer guides, specifications, or anything where consistent terminology matters across a lot of pages: ProWritingAid. The consistency reports are more useful for that kind of work than anything Grammarly offers.
A lot of technical writers end up with both. Grammarly runs in the background for day-to-day writing, and ProWritingAid gets used for the proper review pass before publishing something important. They cover different parts of the editing process, so using both isn't as redundant as it sounds.