---
title: "Project a valid source and declared protocol version"
description: "Native projection first validates the source and checks that the requested MCP protocol version appears at the root. Fix source errors or select a declared version. These failures "
source: "https://mcpdesc.org/docs/rules/0.9.0-rc.3/mcpdesc/projection-source-valid/"
---

Native projection first validates the source and checks that the requested MCP protocol version appears at the root. Fix source errors or select a declared version. These failures come from the projection operation, not a new document-validation phase.

## Requirement

Native projection starts from a document without validation errors and from a protocol version in its root protocolVersions.

## Details

**Rule ID:** `mcpdesc.projection.source-valid`  
**Owner:** mcpdesc  
**Surface:** Native projection  
**Kind:** mcpdesc-semantic  
**Requirement level:** must  
**Status:** delegated · **Enforcement:** external

## Protocol version applicability

| 2024-11-05 | 2025-03-26 | 2025-06-18 | 2025-11-25 | 2026-07-28 |
| ---------- | ---------- | ---------- | ---------- | ---------- |
| applies    | applies    | applies    | applies    | applies    |

## Required by

* **MCP Description 0.9.0, Section 4.14, steps 1 and 2**  
  * 4\. Versioning: [req-native-projection-source-valid](https://mcpdesc.org/docs/specification/0.9.0-rc.3/versioning#req-native-projection-source-valid)
  * 1. Versioning: [req-native-projection-protocol-version-declared](https://mcpdesc.org/docs/specification/0.9.0-rc.3/versioning#req-native-projection-protocol-version-declared)

## Notes

Implemented by @mcpdesc/core; this repository checks the fixtures with scripts/test-projection-fixtures.mjs.

## Examples

### Projection fails

Source: [projection-fixtures/tool-source-invalid.json](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft/projection-fixtures/tool-source-invalid.json) · Selected: `/expectedError`

```json
"projection-source-invalid"
```

### Projection fails

Source: [projection-fixtures/tool-protocol-version-not-declared.json](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft/projection-fixtures/tool-protocol-version-not-declared.json) · Selected: `/expectedError`

```json
"projection-protocol-version-not-declared"
```

### Projection fails

Source: [projection-fixtures/prompt-protocol-version-not-declared.json](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft/projection-fixtures/prompt-protocol-version-not-declared.json) · Selected: `/expectedError`

```json
"projection-protocol-version-not-declared"
```

## Rule Source Code

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