For platforms, agencies and developers

AI humanizer API: which humanizers actually ship one

Searching for a humanizer API turns up marketing pages rather than documentation. Most tools in this category are browser products with a paste box, and several describe an API they do not publish.

Undetected.ai does not have an API. No endpoint, no key, no programmatic access. This page is the research we did instead: who does have one, what shape it takes, and what to check before you integrate anybody.

The Humanizer

Live rewrite

Paste your AI-written text

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Tone

Strength:

2 free runs a day, up to 200 words each. We save your run so you can get back to it, and a delete button appears with the result. See privacy.

AI-pattern score

This is our own AI-pattern score, measured here on sentence rhythm, template phrases, vocabulary variety and passive voice. It is not a GPTZero, Turnitin, Originality.ai, Copyleaks or ZeroGPT result, and it does not predict one. Worth knowing: we also ask the rewrite to vary sentence length, drop template phrases and prefer the active voice, so some of the drop is built in. Read the two panels below, not just the number.

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After ·

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See who publishes an API See our pricing

Browser product · Vendor claims dated · No API here, and none announced

The short answer

Only a minority of AI humanizers publish a real API. Undetectable.ai includes one on every paid tier, which is the cheapest self-serve route in. WriteHuman publishes a documented REST API priced by word, with JavaScript, Python and cURL examples. Walter Writes does not document a REST API but does ship an MCP server, as does WriteHuman, so an AI agent can call the humanize step as a tool. QuillBot has no public paraphrase or humanize API at all. Undetected.ai has no API either: it is a browser product, and we would rather say that here than let you find out after you have planned an integration around it.

Last updated August 22, 2026. Competitor API and MCP availability was read off each vendor's own documentation on July 31, 2026.

What an API is for

Three things teams build with a humanizer API

These are good reasons to want one, and good reasons to choose a vendor that has one rather than a vendor that describes one.

A humanize step in a product

If your app generates drafts, ads, listings or descriptions with a model, the humanize call becomes the last stage of the generation pipeline. Your users get output that reads like a person wrote it, and you never build the rewriting layer yourself.

A bulk pass over a backlog

Agencies and publishers with hundreds of AI-assisted drafts want them run in a batch rather than one by one. This is the use case a paste box genuinely cannot serve, however good the rewrite is.

A pre-publish gate in a CMS

Score every draft on the way to publish and hold back the ones that read as machine-written. This one needs a score in the response, not just a rewrite, which is worth checking vendor by vendor: several return text alone.

What Undetected.ai is

A browser product, described accurately

So there is no confusion about what you would be buying. Everything in this table is something you can check on this page, today, without an account.

Question	Answer
Programmatic access	None. There is no endpoint and no API key, and no date has been committed to for one.
Agent callable (MCP)	No.
Input	Text pasted into the box on this page, plus the tone you want (standard, academic, casual or SEO) and a light-to-strong strength control.
Output	Humanized prose that preserves the facts, argument and structure of the original.
The score	Our own AI-pattern score, measured on sentence rhythm, template phrases, vocabulary variety and passive voice, shown before and after with the reasons behind each number. It is not a GPTZero, Turnitin, Originality.ai, Copyleaks or ZeroGPT reading, and we have no access to those services.
Volume	Up to 1,500 words a run. Planned plans carry a monthly allowance of words and runs: 15,000 words across 60 runs a month at $9, up to 250,000 words across 400 runs a month at $39. Pricing is planned, not yet available. You cannot buy Undetected.ai today. These are the prices we intend to launch with. The humanizer itself is live: create a free account and use it now.
Data handling	Your text and its rewrite are stored for 90 days so you can get back to them, then deleted; you can delete any of them yourself sooner. We train nothing on them. Processing goes through Google's Gemini API — the privacy page states what Google may do with text on the tier we run on today.

The landscape

Which AI humanizers actually ship an API

Each vendor's own docs were read on July 31, 2026. If a row says the pricing is not published, that is because the vendor does not publish it, not because we did not look.

Tool	API	Agent callable (MCP)	How access works
Undetectable.ai	Yes, and unusually it is included on every paid tier rather than gated behind an enterprise plan	Not published	Self-serve. Buy any plan from about $5 a month billed yearly and the API comes with it
WriteHuman	Yes, a documented REST API with JavaScript, Python and cURL examples, priced by word	Yes, it publishes an MCP server	Self-serve, word-priced separately from the browser plans
Walter Writes AI	Not documented publicly	Yes, it publishes an MCP server	Browser plans from $8 a month billed yearly; the MCP server is the programmatic route
QuillBot	No publicly documented paraphrase or humanize API	No	Browser and extension only, at $8.33 a month billed yearly
Undetected.ai (us)	No. Browser only	No	Paste into the box. If an integration is what you need, one of the rows above is your answer, not this one
The detectors	Copyleaks, Originality.ai and GPTZero all sell detection APIs, and none of them sells a humanizer	Varies	Useful as the scoring half of a pipeline, never the rewriting half

Two things in that table are worth acting on. First, if you want the cheapest possible programmatic access with no sales conversation, Undetectable.ai bundling the API into every paid tier is genuinely hard to beat, and it is the recommendation even though it costs us the reader. Second, MCP is the interesting shift: two vendors now ship servers that let an AI agent call the humanize step as a tool, which means the rewrite can happen inside an agent workflow rather than inside your application code. If you are building agents rather than apps, ask about MCP before you ask about REST.

We keep every vendor claim on this site dated and re-checked. The full method, and every claim in this category you can verify for nothing, is in the AI humanizer that actually works.

Before you integrate anyone

What matters when the rewrite happens inside your own product

When the humanize step is behind your API, your users blame you for a bad one. These are the three questions worth answering before you write the integration.

Does it return a score you can act on?

A humanizer that returns only text forces you to trust it. One that returns a reading lets you gate on a threshold, retry, or show the user something. Ask what the number actually measures, too: an in-house heuristic and a third-party detector result are very different things to build a gate on.

Does the meaning survive?

Synonym-swapping humanizers score well and read badly, and inside an API that failure is invisible until a customer complains. Run your own worst paragraph through every candidate before you compare prices, and read the output rather than the score.

What happens to your customers' text?

Content sent through an API usually belongs to your customers, not to you. Get the retention period, the training policy and the name of the upstream model provider in writing, because "we do not train on it" says nothing about who you passed it to.

Good questions

Questions about the AI humanizer API

Does Undetected.ai have an AI humanizer API?

No. Undetected.ai is a browser product: you paste text, pick a tone, and read the rewrite. There is no endpoint, no API key and no programmatic access, and we are not going to describe one before it exists. If an API is what you need today, the table on this page shows which vendors publish one and how access works at each.

Which AI humanizers have an API?

Fewer than the search results suggest. Read off each vendor's own documentation on July 31, 2026: Undetectable.ai includes an API on every paid tier, and WriteHuman publishes a documented REST API with JavaScript, Python and cURL examples priced by word. Walter Writes does not document a REST API publicly. QuillBot has no public humanize or paraphrase API at all. Undetected.ai does not have one either.

What is the best AI humanizer API?

It depends which constraint binds. For the cheapest self-serve access with no sales conversation, Undetectable.ai bundles an API into every paid tier from about $5 a month billed yearly. For transparent per-word pricing and copy-paste code samples, WriteHuman publishes the clearest documentation. Those are the two worth evaluating first, and neither of them is us.

How do I get an AI humanizer API key?

With the self-serve vendors you buy a plan and the key appears in your dashboard, which is how Undetectable.ai and WriteHuman work. Vendors that price by volume issue the key at onboarding after a rate is agreed. Either way you should have a key in hand and a test call working before you write any integration code, because the shape of the response is what your code has to live with.

Is there a free AI humanizer API?

Not in any usable sense. Free browser tiers in this category run from 125 words per request to 750 words a month, and none of them extends to programmatic access, because an API with a free allowance would be scraped within a day. Some vendors will give you trial credits during an evaluation. Budget for paid access from the start if you are putting this in production.

Can an AI agent call a humanizer as a tool?

Yes, and this is the newest change in the category. WriteHuman and Walter Writes both publish MCP servers, which let an AI agent invoke the humanize step as a tool rather than requiring your application code to make an HTTP call. If you are building agent workflows rather than traditional apps, ask any vendor about MCP support before you evaluate their REST API.

Is there an open-source AI humanizer?

There are open-source projects on GitHub that paraphrase text with a local model, and they are a reasonable starting point if you want to own the whole stack. What they do not give you is a score in the same response, ongoing adjustment as detectors change, or anyone to call when output quality drops. Detection models get updated constantly, so an unmaintained rewriter degrades quietly rather than breaking loudly.

What would I build with a humanizer API?

The three common builds are a humanize step inside a content platform, a bulk pipeline that cleans a batch of AI-assisted drafts before publishing, and a pre-publish check inside a CMS. All three are reasons to want an API, and all three are reasons to pick a vendor that has one rather than a vendor that says it is coming.

Is my text stored or used for training?

In the web app, yes it is stored: your text and its rewrite are saved for 90 days so you can get back to them, then deleted automatically, and you can delete any of them yourself at any time. We train nothing on them. Processing happens through Google's Gemini API, and our privacy page states plainly what Google may do with text on the tier we currently run on. Read that page before you send anything that belongs to a client.

Can I use Undetected.ai for a lot of text without an API?

Up to a point. A run handles up to 1,500 words, and the planned paid plans carry a monthly allowance of both words and runs — 250,000 words across 400 runs on the largest. That is a real volume for a person working through a backlog, and it is not a substitute for an integration, because somebody still has to paste each piece.

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