Invisible watermarks
for text.

Hide a short ID in any text and read it back later: label AI output, let agents sign what they write and trace leaks per recipient. The text looks and copies the same. REST API, MCP server and Agent Skill.

Get Your API Key Read The Docs

Signed by an agent, pasted into a chat:

Release 4.12: exported invoices now include the customer VAT number.

decoded: a=release-bot · 13 invisible characters, 1 API call

and paste it anywhere: it looks the same. Decode it with a free account.

Why TextWatermark?

Steganography

Unicode Precision

Attach invisible Unicode variation selectors to visible characters; the text looks and reads the same.

Reversibility

Lossless Decode

Read the exact payload back after copy-paste between apps, chat and email. Robust mode also reports when the text was cut short or changed.

Integration

Built for Agents

REST API with an OpenAPI schema, a remote MCP server and an Agent Skill. Any language that can send HTTPS works.

Reliability

Transparent Status

Live service health on our public status page. DPAs available on request.

What teams use it for

Five workflows with tested code, costs and limits.

AI apps & agents

Label AI-generated text

An invisible label on every response, streamed or not.

Agent builders

Agents sign their output

Verify origin and unchanged words before trusting a text.

Publishers & companies

Trace leaks per recipient

One identical-looking copy per person, each with an encrypted id.

Writers & legal teams

Prove authorship, detect edits

Unchanged, edited, cut short or not yours: one check tells.

Education

AI tutor answers in student work

Find labelled tutor text in submissions, and use it fairly.

All use cases and which mode to choose →

Developer-Centric Toolkit

API Reference

View Full API Reference

Interactive API Console

Configure your request:

Select Demo Scenario:

API Key (not needed: this console shows sample responses and sends nothing):

POST

JSON Request Body:

Response:

// API response will appear here

Impressed by the demo? Sign up now to integrate TextWatermark with your own content and secure your data.

Create Your Free Account

Straightforward Pricing Plans

Choose the plan that fits your needs. Start for free, scale as you grow.

Monthly

Annual (Save 20%)

Free

$0/mo

100 credits to get started

100 one-time credits
Fast & robust watermarking
1 API key

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Frequently Asked Questions

How does text watermarking work?

We attach invisible Unicode variation selectors to the visible characters of your text. The words, spacing and layout stay exactly the same; the selectors carry your payload (for example a document or recipient id), and the API reads it back later. Normalizing the text, retyping it, OCR or having a model rewrite it removes the selectors, so treat the mark as evidence when it is present, not as proof of origin when it is absent.

Is the watermarking process secure?

It depends on the mode. A plain watermark is hidden, not encrypted: anyone with a TextWatermarking API token can read it, so embed an opaque id (for example doc-8841) and keep the details in your own system. For private payloads, create a signing channel and bind your API token to it; the payload is then encrypted with AES-256-GCM and only tokens on that channel can read it, and changed text fails the check. All API traffic uses HTTPS.

What are the limits on Unicode character embedding?

Any script works as the carrier text, including Turkish, Arabic, CJK and emoji, and the payload can be any UTF-8 string. The limit is length: each mode needs a minimum number of visible characters for a given payload (plain mode needs very little; keyed and robust modes need about 8 visible characters per payload byte). The MCP tool watermark_capacity checks this for free before you spend a credit.

Do you offer uptime guarantees or SLAs?

We don't offer a contractual uptime SLA today. You can see live service health on our status page. If you need specific support commitments for your use case, contact us and we'll tell you honestly what we can provide.

Invisible watermarks for text.