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

# Versioning Published MCP Servers

<Note>
  The MCP Registry is currently in preview. Breaking changes or data resets may occur before general availability. If you encounter any issues, please report them on [GitHub](https://github.com/modelcontextprotocol/registry/issues).
</Note>

MCP servers **MUST** define a version string in `server.json`. For example:

```json server.json highlight={6} theme={null}
{
  "$schema": "https://static.modelcontextprotocol.io/schemas/2025-12-11/server.schema.json",
  "name": "io.github.username/email-integration-mcp",
  "title": "Email Integration",
  "description": "Send emails and manage email accounts",
  "version": "1.0.0",
  "packages": [
    {
      "registryType": "npm",
      "identifier": "@username/email-integration-mcp",
      "version": "1.0.0",
      "transport": {
        "type": "stdio"
      }
    }
  ]
}
```

The version string **MUST** be unique for each publication of the server. Once published, the version string (and other metadata) cannot be changed.

## Version Format

The MCP Registry recommends [semantic versioning](https://semver.org/), but supports any version string format. When a server is published, the MCP Registry will attempt to parse its version as a semantic version string for sorting purposes, and will mark the version as "latest" if appropriate. If parsing fails, the version will always be marked as "latest".

<Warning>
  If a server uses semantic version strings but publishes a new version that does *not* conform to semantic versioning, the new version will be marked as "latest" even if it would otherwise be sorted before the semantic version strings.
</Warning>

As an error prevention mechanism, the MCP Registry prohibits version strings that appear to refer to ranges of versions.

| Example        | Type                | Guidance                       |
| -------------- | ------------------- | ------------------------------ |
| `1.0.0`        | semantic version    | **Recommended**                |
| `2.1.3-alpha`  | semantic prerelease | **Recommended**                |
| `1.0.0-beta.1` | semantic prerelease | **Recommended**                |
| `3.0.0-rc.2`   | semantic prerelease | **Recommended**                |
| `2025.11.25`   | semantic date       | Recommended                    |
| `2025.6.18`    | semantic date       | Recommended **(⚠️Caution!⚠️)** |
| `2025.06.18`   | non-semantic date   | Allowed **(⚠️Caution!⚠️)**     |
| `2025-06-18`   | non-semantic date   | Allowed                        |
| `v1.0`         | prefixed version    | Allowed                        |
| `^1.2.3`       | version range       | Prohibited                     |
| `~1.2.3`       | version range       | Prohibited                     |
| `>=1.2.3`      | version range       | Prohibited                     |
| `<=1.2.3`      | version range       | Prohibited                     |
| `>1.2.3`       | version range       | Prohibited                     |
| `<1.2.3`       | version range       | Prohibited                     |
| `1.x`          | version range       | Prohibited                     |
| `1.2.*`        | version range       | Prohibited                     |
| `1 - 2`        | version range       | Prohibited                     |
| `1.2 \|\| 1.3` | version range       | Prohibited                     |

## Best Practices

### Use Semantic Versioning

Use [semantic versioning](https://semver.org/) for version strings.

### Align Server Version with Package Version

For local servers, align the server version with the underlying package version in order to prevent confusion:

```json server.json highlight={2,7} theme={null}
{
  "version": "1.2.3",
  "packages": [
    {
      "registryType": "npm",
      "identifier": "@my-username/my-server",
      "version": "1.2.3",
      "transport": {
        "type": "stdio"
      }
    }
  ]
}
```

If there are multiple underlying packages, use the server version to indicate the overall release version:

```json server.json highlight={2,7,15} theme={null}
{
  "version": "1.3.0",
  "packages": [
    {
      "registryType": "npm",
      "identifier": "@my-username/my-server",
      "version": "1.3.0",
      "transport": {
        "type": "stdio"
      }
    },
    {
      "registryType": "nuget",
      "identifier": "MyUsername.MyServer",
      "version": "1.0.0",
      "transport": {
        "type": "stdio"
      }
    }
  ]
}
```

### Align Server Version with Remote API Version

For remote servers with an API version, the server version should align with the API version:

```json server.json highlight={2,6} theme={null}
{
  "version": "2.1.0",
  "remotes": [
    {
      "type": "streamable-http",
      "url": "https://api.myservice.com/mcp/v2.1"
    }
  ]
}
```

### Use Prerelease Versions for Registry-only Updates

If you anticipate publishing a server multiple times *without* changing the underlying package or remote URL — for example, to update other parts of the metadata — use semantic prerelease versions:

```json server.json highlight={2} theme={null}
{
  "version": "1.2.3-1",
  "packages": [
    {
      "registryType": "npm",
      "identifier": "@my-username/my-server",
      "version": "1.2.3",
      "transport": {
        "type": "stdio"
      }
    }
  ]
}
```

<Warning>
  According to semantic versioning, prerelease versions such as `1.2.3-1` are sorted before regular semantic versions such as `1.2.3`. Therefore, if you publish a prerelease version *after* its corresponding regular version, the prerelease version will **not** be marked as "latest".
</Warning>

## Aggregator Recommendations

MCP Registry aggregators **SHOULD**:

1. Attempt to interpret versions as semantic versions when possible
2. Use the following version comparison rules:
   * If one version is marked as "latest", treat it as later
   * If both versions are valid semantic versions, use semantic versioning comparison rules
   * If neither versions are valid semantic versions, compare published timestamp
   * If one version is a valid semantic version and the other is not, treat the semantic version as later
