---
title: "List supported MCP protocol versions in protocol scopes"
description: "Root and declaration protocolVersions arrays are non-empty, contain no duplicates, and name only MCP protocol versions this specification supports."
source: "https://mcpdesc.org/docs/rules/0.9.0-rc.3/mcpdesc/protocol-versions-values/"
---

Root and declaration protocolVersions arrays are non-empty, contain no duplicates, and name only MCP protocol versions this specification supports.

## Requirement

A protocolVersions array is non-empty, has unique values, and contains only supported MCP protocol-version identifiers.

## Details

**Rule ID:** `mcpdesc.protocol-versions.values`  
**Owner:** mcpdesc  
**Surface:** Document, scoped declarations  
**Kind:** structural  
**Requirement level:** must  
**Protocol versions:** independent of the MCP protocol version  
**Document schema locations:** `#/$defs/protocolVersionScope`, `#/$defs/supportedProtocolVersion`  
**Status:** internal · **Enforcement:** internal

## Required by

* **MCP Description 0.9.0, Section 4**  
  * 4\. Versioning: [req-protocol-versions-values](https://mcpdesc.org/docs/specification/0.9.0-rc.3/versioning#req-protocol-versions-values)

## Examples

### Invalid example

Source: [expected-invalid/closed-protocol-enum.json](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft/fixtures/expected-invalid/closed-protocol-enum.json) · Selected: `/protocolVersions/0`

```json
"2027-01-01"
```

## Rule Source Code

[document.yaml](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft/validation/rules/document.yaml) at immutable tag [v0.9.0-rc.3](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft).