Grammar
Replace “are” with “is”.
Grammar Checker APIGrammar correction for production workflows.
Correct grammar, spelling, and punctuation while preserving voice, meaning, language, and paragraph structure. Get corrected text plus a complete word-level diff.
Input
12 words
This are a sample sentence with some grammar mistake inside of it.
Corrected text
- Result 2 edits
- Input words 12
- Changed true
- Variant Auto
Agreement
Replace “mistake” with “mistakes”.
Input
12 words
curl -X POST https://developer-portal.walterwrites.ai/api/grammar/correct/
-H "Content-Type: application/json"
-H "X-API-Key: YOUR_API_KEY"
-d '{
"content": "This are a sample sentence with some grammar mistake inside of it."
}'
Output
"status": "success",
"corrected_text": "This is a sample sentence with some grammar mistakes inside of it.",
"diff": [
{ "type": "replace", "original": "are", "corrected": "is", "start": 5, "end": 8 },
{ "type": "replace", "original": "mistake", "corrected": "mistakes", "start": 45, "end": 52 }
],
"edits_count": 2,
"changed": true,
"input_words": 12Build grammar review into any writing product.
A synchronous endpoint with a complete diff, stable character offsets, and optional English-variant targeting.
Complete word-level diff
Render track changes from replace, insert, and delete operations that reference the submitted text.
Minimal-change correction
Correct writing mechanics while preserving voice, meaning, language, and paragraph structure.
English variant control
Use automatic detection or target en-US, en-GB, en-CA, en-AU, or en-IN.
Clean-text handling
Text that needs no correction is returned unchanged with an empty diff.
Safe retries
Use an idempotency key to avoid duplicate processing and duplicate charges during retries.
Script-aware billing
The response returns the word count used for billing, with 1 credit charged per word.
Pair grammar correctionwith the rest of Walter.
Use one developer portal and scoped API keys for humanization, AI text detection, grammar correction, plagiarism scanning, and AI image detection.
AI Detector API
LiveAnalyze text for AI-generated content with confidence scores and sentence-level details.
AI Humanizer API
LiveTransform AI-generated text into natural, human-like content through a documented REST endpoint.
AI Voice Detector API
Coming soonAudio detection is planned for a future Walter API release.
Plagiarism Checker API
LiveScan text against web sources and return a score, matched URLs, and highlighted character ranges.
Grammar Checker API
LiveCorrect grammar, spelling, and punctuation and return corrected text plus a complete word-level diff.
AI Image Detector API
LiveUpload an image and receive a real, fake, or inpainting verdict with confidence and per-class probabilities.
Start free. One credit pool, every API.
Grammar corrections use 1 credit per word. Every request returns the script-aware word count used for billing.
Need enterprise pricing?
Talk to us about higher-volume workloads and enterprise deployment requirements.
Frequently asked questions.
Documented answers about the endpoint, response, limits, billing, and safe production use.
Is the Walter Grammar Checker API live?
Yes. Send a POST request to /api/grammar/correct/ with an API key that has the grammar_checker scope.
What does the Grammar Checker API return?
It returns corrected text, a complete word-level diff, issue notes, edit counts, input counts, execution time, and the remaining credit balance. Diff offsets refer to the text exactly as submitted.
What are the request limits?
Requests must contain at least 5 words and may contain up to 10,000 words or 75,000 characters.
How is grammar checking billed?
Grammar correction costs 1 credit per word using the API’s script-aware count. Failed corrections are refunded automatically.
Can I select an English variant?
Yes. Set target_variant to auto, en-US, en-GB, en-CA, en-AU, or en-IN. Auto is the default and preserves the input’s variant.
How should retries be handled?
Send an Idempotency-Key header. Reusing the same key with the same text within five minutes returns the original response without another charge.
Ship your first Grammar Checker API request.
Create an API key with the required scope, follow the documented request format, and keep the returned evidence in your existing review workflow.
Developer resources.
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