# Coauthor Coauthor is a set of tools, instructions, and skills that let AI agents read and edit the CKEditor 5 documents of your users. Your agent connects to them through an MCP server in CKEditor Cloud Services. Your backend can call the same tools over REST, without an AI model. Coauthor runs CKEditor 5 on the server, with the editor bundle that you upload to Cloud Services. It checks every edit in this editor before it applies the edit. The agent’s edits reach the document as direct changes or as Track Changes suggestions. Coauthor runs no AI model of its own. You choose the agent and its model. To learn what Coauthor is for and when to use it, see [Coauthor](../../../../../ckeditor5/latest/features/editing-toolkit/editing-toolkit-coauthor.md) in the CKEditor 5 documentation. This guide shows how to set up Coauthor and connect your agent to it. ![Your agent asks Coauthor for changes. The changes arrive in the document as suggestions, and people accept or reject each one.](https://ckeditor.com/docs/cs/latest/assets/img/agent-toolkit/overview.png) > **Note** > > Coauthor is in Early Access, in CKEditor Cloud Services only. See [Availability](#availability). ## What Coauthor adds to your agent Without Coauthor, your agent gets the HTML through your API, rewrites it with its own tools, and saves it back. With Coauthor, the agent sends each edit to Coauthor, which checks it in your editor and applies it as a separate change. People can review each change. * **Editor compatibility.** Coauthor tells the agent which features your editor has, such as charts or footnotes, and gives it a short guide for each one. Coauthor validates each edit using CKEditor 5 and your editor bundle before applying it. * **No lost content.** Coauthor rejects edits that would result in lost content, such as a chart, a style, or a comment that your editor would drop. It tells the agent what would be lost, so the agent can correct the edit and try again. An agent that rewrites the HTML does not learn what your editor drops. * **Review by users.** The agent’s edits arrive as separate, granular changes, not as a rewritten document. Users can review and accept or reject the agent’s suggested changes. * **Editing at the same time.** Users can keep writing while the agent works, and the agent’s edits merge with their changes. Saving a rewritten document could overwrite changes made by other users. * **Limited access.** [Permissions](permissions.md) limit what the agent can do. An agent that saves through your API can save anything that the API allows. To learn how Coauthor handles an edit, see [How Coauthor works](how-it-works.md). ## Agents and models Coauthor works with any agent framework and any model, including small ones. Your agent needs no library to use it. * **Any MCP client.** Your agent connects to one MCP address. Claude Code, Cursor, and agents that you build with the Claude Agent SDK, the OpenAI Agents SDK, the Vercel AI SDK, LangChain, or your own code can all use it. * **Frontier models.** Your agent can use the leading models from OpenAI, Anthropic, and Google, such as GPT-6 Sol, Claude Opus 5.5, Claude Sonnet 5.5, and Gemini 4 Argon. * **Small models.** We build and test Coauthor on small, low-cost models, such as Claude Haiku 5.5, GPT-6 Luna, and DeepSeek V4.1 Flash. * **Open-weight models.** Your agent can use a model that you host yourself, such as gpt-oss-120b, Qwen3.8-27B, Mistral Large 4, or Kimi K3.1 Pro. * **Your infrastructure.** The agent may run on a user’s computer or in a cloud. To connect your agent, see [Connect an agent](connect-an-agent.md). ## Use cases [](../../../../../ckeditor5/latest/features/editing-toolkit/use-cases/editing-toolkit-agent-apps.md)[](../../../../../ckeditor5/latest/features/editing-toolkit/use-cases/editing-toolkit-custom-chat.md)[](../../../../../ckeditor5/latest/features/editing-toolkit/use-cases/editing-toolkit-backend-agents.md)[](../../../../../ckeditor5/latest/features/editing-toolkit/use-cases/editing-toolkit-with-ckeditor-ai.md)[](../../../../../ckeditor5/latest/features/editing-toolkit/use-cases/editing-toolkit-deterministic-scripts.md) ## Coauthor or CKEditor AI CKEditor AI is our agent, built into your editor. Coauthor lets your own agent edit the documents, wherever the agent runs. You can use CKEditor AI and Coauthor with the same documents. | | CKEditor AI | Coauthor | | ---------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- | | **The agent** | Ours. You add your style guide and tools with [extensions](../../ckeditor-ai/extensions/overview.md). | Yours, with your prompts and tools. | | **Where users work with it** | [AI Chat, Quick Actions, Review and Translate](../../../../../ckeditor5/latest/features/ai/ckeditor-ai-overview.md) in your editor, and [Document Processing](../../ckeditor-ai/document-processing.md) from your backend. | Wherever your agent runs. The editor gets no new AI buttons. | | **The model** | Our [models](../../ckeditor-ai/models.md) on SaaS, paid with [AI credits](../../ckeditor-ai/usage-and-billing.md). Your own [providers](../../ckeditor-ai/extensions/model-providers.md) on-premises. | Your agent’s model, billed by your provider. No other model sees your documents. | | **How edits arrive** | The user previews the changes, then applies them or adds them as suggestions. | Separate, granular changes, applied directly or as suggestions, merged with what users typed. | | **What you build** | The [AI plugins](../../../../../ckeditor5/latest/features/ai/ckeditor-ai-integration.md) and a [token endpoint](../../ckeditor-ai/authentication.md). | Your agent, a backend that signs its tokens, and an editor bundle with `DocumentCompare`. See [Set up your environment](set-up.md). | | **Deployment** | [SaaS](../../ckeditor-ai/saas.md) or [on-premises](../../ckeditor-ai/on-premises.md). | SaaS, in Early Access. On-premises is coming soon. | ## Availability * **CKEditor Cloud Services (SaaS):** in Early Access. We turn on Coauthor for an environment that you already have, or for a trial environment. [Contact us](https://ckeditor.com/contact/) to join. * **On-premises:** coming soon. ## Next steps * **[Quick start](quick-start.md):** edit a document in a trial environment, first with Claude Code, then with your own code. * **[How Coauthor works](how-it-works.md):** follow one job from the agent’s first call to the change in the document. * **[Set up your environment](set-up.md):** connect your own agent. * **[Security and compliance](security-and-compliance.md):** how Coauthor handles and protects your document data. --- Full index of the Cloud Services documentation: [llms.txt](../../../../llms.txt)