It's one of the most common searches in this space: "Grammarly API." The short answer is yes — Grammarly operates a developer platform with real REST APIs. The longer answer surprises most people: none of those APIs correct grammar. You cannot send text to Grammarly and get back a list of corrections to render in your own product.

This article explains what Grammarly's developer APIs actually do as of August 2026, where they genuinely fit, and which proofreading APIs to evaluate when corrections — not scores — are the requirement.

What Grammarly's developer platform offers

The platform at developer.grammarly.com is a set of enterprise APIs authenticated with OAuth 2.0:

  • Analytics API — organization-level usage and engagement reporting.
  • License Management API — administer seats and subscriptions programmatically.
  • Writing Score API — upload a document, receive a numeric quality score.
  • AI Detection API (beta) — estimate whether text was AI-generated.
  • Plagiarism Detection API (beta) — check text against web sources.

Read that list as a product manager and a pattern emerges: these APIs measure writing and administer Grammarly accounts. They are built for enterprises that already use Grammarly and want to fold it into BI dashboards, compliance checks, and content gates. Grammarly previously offered an embeddable Text Editor SDK that rendered its own suggestion UI inside your app, but the current developer platform no longer lists it — the focus has moved to the evaluation APIs above.

A closer look: the Writing Score API

The Writing Score API is the closest thing Grammarly has to a "check this text" endpoint, so it deserves a careful look. The flow is asynchronous and file-based:

# 1. Create a score request
curl -X POST 'https://api.grammarly.com/ecosystem/api/v2/scores' \
  -H 'Authorization: Bearer <ACCESS_TOKEN>' \
  -H 'Content-Type: application/json' \
  -d '{ "filename": "article.docx" }'
# → { "score_request_id": "...", "file_upload_url": "https://..." }

# 2. Upload the file to the pre-signed URL (within 120 seconds)
curl -T article.docx "<file_upload_url>"

# 3. Poll for the result
curl 'https://api.grammarly.com/ecosystem/api/v2/scores/<score_request_id>' \
  -H 'Authorization: Bearer <ACCESS_TOKEN>'

The completed response contains five numbers — a general score plus engagement, correctness, delivery, and clarity:

{
	"status": "COMPLETED",
	"score": {
		"general_score": 0.86,
		"engagement": 0.86,
		"correctness": 0.89,
		"delivery": 0.86,
		"clarity": 0.83
	}
}

The constraints tell you what this API is for. Documents can be up to 4 MB and 100,000 characters with a 30-word minimum; formats are .doc, .docx, .odt, .txt, and .rtf. New score requests are capped at 10 per second, and Grammarly retains uploaded documents for at most 24 hours.

This is a well-designed API for scoring documents at scale: gating a CMS publish button on a minimum correctness score, tracking writing quality across a support team, or sampling content for review. It is not designed for, and cannot be used for, showing a user what to fix — the response contains no issues, no ranges, and no replacements.

What you can't build with it

If your product idea involves any of the following, Grammarly's platform is a dead end:

  • Underlining errors in your own editor — there are no edit ranges to underline.
  • Suggestion cards with accept/reject — there are no suggestions to accept.
  • Real-time, as-you-type checking — an asynchronous file-upload flow with polling cannot keep up with keystrokes.
  • Your own brand on the correction experience — without an embeddable UI or raw edits, there is no experience to brand.

This isn't a criticism of Grammarly's strategy; it's a boundary. Correction is the company's consumer product, and its APIs serve the enterprise around that product. If you need corrections inside your product, you need a proofreading API instead.

What a correction API looks like

For contrast, here is the same interaction against AmberPen — synchronous, text-in, edits-out:

curl https://api.amberpen.dev/proofread \
  -H "authorization: Bearer $AMBER_PEN_API_KEY" \
  -H "content-type: application/json" \
  -d '{ "text": "The new settings works across every workspace." }'
{
	"mode": "correct",
	"edits": [
		{
			"id": 0,
			"start": 17,
			"end": 22,
			"original": "works",
			"replacement": "work"
		}
	]
}

Each edit is an exact range in the text you sent, plus its replacement. Your app decides everything else: underline the range, show a popover, let the user accept or dismiss, log nothing. An optional evaluate pass adds a plain-language explanation, a category, and relevance-ranked replacements to every edit. Median response time is 217 ms, fast enough for as-you-type checking — see the benchmarks for methodology.

Alternatives that return real corrections

API Notes Watch out for
AmberPen Structured edits with explanations, streaming, incremental re-checking, custom dictionaries; leads JFLEG fluency and CWEB recall benchmarks Second to GrammarBot Neural on CWEB precision
Sapling Neural edits API with SDKs and a broader writing-assistant feature set 620 ms median latency; lower precision on web text
GrammarBot Neural Highest CWEB precision in our AmberPen vs GrammarBot Neural comparison ~1 s median latency — batch, not real-time
LanguageTool Open source, self-hostable, broad language support Rule-based recall ceiling (found 18% of CWEB errors)
Harper Free, runs entirely on-device, ~2 ms per sentence English only; much lower measured quality
Trinka Academic and technical writing, on-premise option Custom enterprise pricing; unpublished latency

Our grammar checker API comparison goes deeper on each, including pricing models and benchmark detail.

The decision in one paragraph

Choose Grammarly's developer APIs when you already run Grammarly Enterprise and want to measure writing quality or administer licenses — the Writing Score API does that job well. Choose a proofreading API when your product needs to show and apply corrections: you want structured edits, real-time latency, vocabulary control, and pricing that scales with characters rather than seats. For that second job, you can create a free AmberPen test key and make your first corrected request in minutes.

Before you commit to any of them, two things are worth checking yourself: how grammar correction is measured, so you can read every vendor's quality claims skeptically, and what you'll actually pay, which models per-seat, per-character, and per-token billing against the same workload.