> ## Documentation Index
> Fetch the complete documentation index at: https://docs.0mcp.io/llms.txt
> Use this file to discover all available pages before exploring further.

# MCP 2026-07-28 compatibility

> Understand how 0mcp works with the MCP 2026-07-28 protocol era, Streamable HTTP, version negotiation, and client compatibility.

MCP 2026-07-28 is a major protocol update.

It changes how modern clients discover servers, identify requests, and communicate over HTTP. 0mcp uses **Streamable HTTP** and is being aligned with this newer protocol era while continuing to support practical client compatibility during rollout.

<Info>
  Client behavior depends on the MCP client you use. Some clients may still use an older protocol era even when the server is ready for newer behavior.
</Info>

## What changed

The 2026-07-28 protocol era moves remote MCP toward stateless HTTP requests.

Important changes include:

* Session identifiers are no longer part of the modern HTTP flow.
* Modern clients use `server/discover` to learn supported protocol versions and capabilities.
* Requests carry protocol version and identity metadata with each request.
* Modern HTTP requests include MCP headers such as `Mcp-Protocol-Version`, `Mcp-Method`, and `Mcp-Name`.
* Server results include protocol-managed result metadata.
* Long-lived resource subscriptions use newer subscription behavior instead of the older resource subscribe methods.
* Older utilities such as `ping` and `logging/setLevel` are removed or deprecated in the modern era.

For the formal specification, use the official [Model Context Protocol specification](https://modelcontextprotocol.io/specification).

## How 0mcp serves remote MCP

0mcp serves your published MCP server over **Streamable HTTP**.

Your hosted endpoint is shown on the server **Setup** page. It usually looks like:

```text theme={null}
https://your-server.0mcp.io/mcp
```

If you configure a verified custom domain, your Setup page shows the custom MCP endpoint instead.

0mcp keeps the hosted MCP layer separate from your upstream API. The MCP client calls 0mcp, and 0mcp forwards tool requests to your API according to the published server version.

## Version negotiation

Modern MCP clients can negotiate the protocol era with the server.

During rollout, this matters because not every client upgrades at the same time.

* A modern client can discover newer behavior automatically.
* A legacy client may continue using older initialization behavior.
* Some clients may require a restart before they refresh capabilities or configuration.

0mcp documentation avoids claiming universal MCP 2026-07-28 behavior for every client. The server endpoint is designed for Streamable HTTP compatibility, but the active protocol era depends on the client implementation.

## Published versions still control capabilities

The MCP protocol version does not change 0mcp's release model.

Connected clients only see the **published version** of your server.

Draft edits remain private until you publish a new version. After publishing, reconnect the client if it still shows an older tool, resource, or prompt list.

## Authentication and OAuth

0mcp uses pass-through authentication for upstream API credentials.

If your published tools require Bearer tokens or API keys, the Setup page shows the headers or environment variables your client must provide.

For OAuth-protected MCP tools, 0mcp also exposes MCP OAuth setup details when required, including:

* The MCP resource URL.
* Protected resource metadata URLs.
* Any configuration issue that must be fixed before client setup is usable.

Configure the OAuth issuer and JWKS details from server **Settings** when your source requires MCP OAuth metadata.

<Warning>
  Signing in to 0mcp does not authenticate calls to your upstream API. Your API still decides whether each forwarded request is allowed.
</Warning>

## Browser and CORS behavior

Browser-based MCP clients perform CORS preflight checks before making remote MCP requests.

Modern MCP requests may include protocol headers such as:

```text theme={null}
Mcp-Protocol-Version
Mcp-Method
Mcp-Name
```

If a browser client cannot complete the preflight request, it may fail to connect or fall back to older behavior depending on the client.

When troubleshooting browser or web playground issues, verify the request reaches 0mcp and that the client is using the endpoint copied from **Setup**.

## What this means for you

For most 0mcp users, the workflow stays the same:

1. Import an API source.
2. Review the generated tools.
3. Publish a version.
4. Copy the generated client configuration from **Setup**.
5. Reconnect the MCP client.

The protocol update mainly affects client compatibility, connection diagnostics, and the exact HTTP headers used by modern clients.

## Troubleshooting checklist

If a client does not connect:

* Confirm the server has a published version.
* Confirm serving is enabled.
* Copy the MCP endpoint again from **Setup**.
* Verify the client supports remote Streamable HTTP.
* Check whether the client requires authentication headers or OAuth setup.
* Restart or reconnect the client.
* Review [MCP connection issues](/troubleshooting/mcp-connection-issues).

If a client connects but capabilities look stale, see [Tool discovery problems](/troubleshooting/tool-discovery-problems).