</> Developer API

Do more with the
AI Humanizer API

Use our state-of-the-art API to detect and humanize AI content

Starting at $0.10 per 1K words.

View Pricing View Documentation
const res = await fetch("https://v2-humanizer.rephrasy.ai/api/", {
  method: "POST",
  headers: {
    "Authorization": "Bearer <your-api-key>",
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    text: "AI-generated text here.",
    model: "v3",
    words: true
  })
});

const data = await res.json();
// => { output: "Humanized text...", costs: { total: 1.5 } }
200 OKREST API v1

AI-friendly integration

Paste the Rephrasy API context into your AI tool and ask it to build your integration with you.

/rephrasy.ai/llms.txt
Use ClaudeUse ChatGPTUse Lovable
Text HumanizerText DetectorImage Humanizer
POST /api/v2-humanizer.rephrasy.ai

Text Humanizer API

Detect and humanize AI-generated text at scale — rewrite it to read naturally and pass AI detectors. A simple, fast, reliable JSON API.

From $0.10 / 1K wordsFlat or word-based billing

Authentication

Authorization: Bearer <your-api-key>

All requests and responses are JSON.

Credits

Two billing modes. Flat: 1 credit per call. Word-based (words: true): 0.1 credit flat + 0.1 credit per 100 words. Add costs: true to see the exact charge in the response.

const res = await fetch("https://v2-humanizer.rephrasy.ai/api/", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_API_KEY",
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    text: "AI-generated text here.",
    model: "v3",
    words: true
  })
});

const data = await res.json();
// => { output: "Humanized text...", new_flesch_score: 68.8 }
200 OKText API v1

Parameters

FieldTypeRequiredDescription
textstringRequiredThe AI-generated text to humanize (max 12,000 chars for plain text).
modelstringRequiredModel to use — v3, Undetectable Model v2, Undetectable Model, or SEO Model; or a Writing Style ID. Each model targets different detectors.
stylestringOptionalOptional style for v3 — creative, journalistic, or professional. Defaults to v3's normal behavior.
wordsbooleanOptionalEnable word-based pricing (default false).
costsbooleanOptionalReturn cost information in the response (default false).
languagestringOptionalOutput language, e.g. English, German, French. Auto-detected if omitted.

Returns output plus new_flesch_score (readability 0–100 — higher is easier to read). 200 OK on success; 401 invalid API key; 422 invalid input.

NEWinput_format

Structured input (HTML / Markdown)

Add the optional input_format field to POST /api/ to send a whole document instead of plain text — only the visible text is humanized and the structure is rebuilt around it.

FieldTypeDefaultDescription
input_formatstring"text""text", "html", or "markdown". With html/markdown, only the visible text is humanized and the document structure is rebuilt around it.

How it works

  1. Parses the document and pulls out only the human-readable text.
  2. Humanizes that text with the model you selected.
  3. Rebuilds the document — tags, attributes, code, and links come back untouched.

Works with every model, including the SEO Model.

Never modified

HTML tag structure, script, style, code and pre blocks, link hrefs, Markdown code fences, inline code, and link URLs.

curl -X POST https://v2-humanizer.rephrasy.ai/api/ \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "ft_clean-v3",
    "input_format": "html",
    "words": true,
    "text": "<article><h1>The Future of Remote Work</h1><p>It is crucial to leverage modern tools.</p><pre><code>keep --this</code></pre></article>"
  }'

# => {
#   "output": "<article><h1>What lies ahead for remote work</h1><p>You really want to make the most of modern tools.</p><pre><code>keep --this</code></pre></article>",
#   "new_flesch_score": 71.2
# }
# The <h1> and <p> text is rewritten; the <code> block is preserved exactly.

Limits & pricing

  • HTML / Markdown input is capped at 200,000 characters (plain text stays at 12,000).
  • Structured input costs 2.5× the normal charge, on both flat and word-based billing.
  • Word-based billing counts only the visible words we rewrite — never the surrounding markup. A 50 KB HTML page wrapping 200 words is billed on those 200 words (× 2.5), not on the markup.
NEW

Model v3 — Best model for GPTZero with advanced style options

Read about the new model and how to use it →

Make sure you check out our
Detector API

POST /detect_apidetector.rephrasy.ai

AI Detector API

Score any text for AI-generated content — an overall 0–100 score (0 = human, 100 = AI), or per-sentence scores in depth mode.

1 credit / call$0.10 per detection · flat

Authentication

Authorization: Bearer <your-api-key>

All requests and responses are JSON.

Credits

Flat: 1 credit per call, regardless of text length. Charged on a successful 200 response.

const res = await fetch("https://detector.rephrasy.ai/detect_api", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_API_KEY",
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    text: "Rephrasy rephrases AI generated text.",
    mode: ""            // "" = overall score, "depth" = per-sentence
  })
});

const data = await res.json();
// => { scores: { overall: 1.4 }, sentences: { ... } }
200 OKDetector API v1

Parameters

FieldTypeRequiredDescription
textstringRequiredThe text to check for AI content.
modestringOptionalDetail level — leave empty for an overall score, or send depth for per-sentence scores.

Returns scores.overall (0–100; 0 = human, 100 = AI). In depth mode, sentences maps each sentence to its score. 200 OK on success; 401 invalid API key; 422 invalid input.

What You Can Build

Developers and agencies use the Rephrasy API to power their own products and workflows.

Bulk Content Pipelines

Process hundreds of articles or documents in parallel. Integrate into your existing content workflow via a single POST request.

SaaS Products

Build your own AI humanizer tool on top of Rephrasy. White-label the API or offer it as a feature inside your product.

Browser Extensions

Call the API from a Chrome extension to humanize text inline — directly on Google Docs, WordPress, or any web editor.

Agency Automation

Connect Rephrasy to Zapier, Make, or n8n to automatically humanize AI drafts before they hit your CMS or client delivery.

NEWsynthid-humanizer.rephrasy.ai

Image Humanizer API

Remove invisible AI watermarks (SynthID, StableSignature), detect AI provenance, and humanize images programmatically. Supports single images and batches up to 100.

10 credits / imageSame credit balance as text API

Authentication

Authorization: Bearer <your-api-key>

Website key = high-priority queue · User API key = normal queue

Credits

Credits are deducted at batch submission. Insufficient balance → 402 error, no images processed. Batches auto-delete after 24 hours.

Also available

GET/batches/{id}
GET/batches/{id}/download
POST/remove/visible
POST /batches
# 1 — Submit batch
curl -X POST https://synthid-humanizer.rephrasy.ai/batches \
  -H "Authorization: Bearer <your-api-key>" \
  -F "files=@photo1.png" \
  -F "files=@photo2.jpg"

# => { "batch_id": "a3f9c2b1", "job_count": 2, "status": "queued" }

# 2 — Poll until done (every 5–10 s)
curl https://synthid-humanizer.rephrasy.ai/batches/a3f9c2b1 \
  -H "Authorization: Bearer <your-api-key>"

# => { "status": "done", "done": 2, "total": 2, "download_ready": true }

# 3 — Download ZIP (batch deleted after this)
curl -O https://synthid-humanizer.rephrasy.ai/batches/a3f9c2b1/download \
  -H "Authorization: Bearer <your-api-key>"
200 OKImage API v1

Batch status values

queuedWaiting in queue — queue_position shows place
processingGPU is working on this batch
doneAll images finished, ready to download
failedProcessing failed — check per-job error field

Error codes

400No files / more than 100 files
401Missing or invalid API key
402Insufficient credits
404Batch not found or already downloaded
425Batch not done yet (too early to download)
NEWv1-humanizer.rephrasy.ai

Custom Writing Styles API

Train a reusable writing style from your own before/after examples, then humanize any text in that style. Perfect for giving every end-user their own voice.

20 credits / training1 credit / humanize call

Authentication

Authorization: Bearer <your-api-key>

All requests and responses are JSON.

Credits

Training a style costs 20 credits, charged only after success. Each humanize call costs 1 credit. No cap on the number of styles — usage is metered by credits.

POST /api/styles
curl -X POST https://v1-humanizer.rephrasy.ai/api/styles \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Client 42 voice",
    "external_ref": "client-42",
    "sentences": [
      {"original": "The product offers many benefits to users.",
       "rewritten": "Honestly? This thing just makes life easier. Here is why."},
      {"original": "It is important to consider several factors.",
       "rewritten": "A few things matter here — let us walk through them."}
    ]
  }'

# => {
#   "style_id": "aB3xY7...",
#   "name": "Client 42 voice",
#   "external_ref": "client-42",
#   "status": "completed"
# }
200 OKWriting Styles API v1

Error codes

400API Key is required — missing Authorization header
400Invalid API Key — key not recognized
400Insufficient Credits for the action
403Writing style does not belong to this user
404Writing style not found
500Failed to analyze writing style — training failed, no credits charged, retry

Notes: styles cannot be deleted via the API. Only styles created with your API key are returned.

Bulk Credits — Unbeatable API Pricing

No per-seat fees, no rate limits. Buy credits once, use them any time. The more you buy, the cheaper each request gets.

5,000

credits

$275

$0.0550 / credit

100k words for $11.00
Most Popular

10,000

credits

$500

$0.0500 / credit

100k words for $10.00

20,000

credits

$950

$0.0475 / credit

100k words for $9.50

50,000

credits

$2,250

$0.0450 / credit

100k words for $9.00

* Based on 100 × 1,000-word requests with word-based pricing enabled (2 credits each = 200 credits total)

Real cost — humanizing 100,000 words

100 requests of 1,000 words each, word-based pricing enabled (words: true):

Rephrasy API (10K bulk)

$10.00

$0.10 per 1K words — no subscription, no monthly cap

WriteHuman Premium

$17.25

$69/mo plan pro-rated for 100K of 400K words

Undetectable AI Premium

$47.25

$15.75/mo × 3 months needed for 100K words

* Competitor prices based on publicly listed plans. WriteHuman: $69/mo Premium. Undetectable AI: $15.75/mo Premium (35K words/mo).

Ready to integrate?

Sign up, subscribe to any plan, and find your API key in your account dashboard. Start making requests in minutes.

Get API KeyAPI Docs

AI Humanizer API designed for developers

Our AI Humanizer API is designed for developers who want to humanize AI generated content in bulk. The API is designed to be simple, fast and reliable. For API only plans, please contact us directly!

  • Get a subscription with Rephrasy

    Rephrase content on the fly with our powerful API.

  • Use the Rephrasy AI Detector

    Detect AI content with our powerful AI detection tool on scale.

  • Combine both, AI Detector and Humanizer for the best results

    Use Rephrasy's AI detector and humanizer together for the best results.

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Convert AI to Human Text — Free AI Humanizer

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