---
title: "Keep newer client input responses closed"
description: "In MCP 2026-07-28, sampling, elicitation, and roots responses are closed input responses rather than open results. Remove undefined fields; _meta is defined only for the sampling r"
source: "https://mcpdesc.org/docs/rules/0.9.0-rc.3/mcp/input-response-closed/"
---

In MCP 2026-07-28, sampling, elicitation, and roots responses are closed input responses rather than open results. Remove undefined fields; \_meta is defined only for the sampling response. Earlier versions’ open-result behavior does not carry forward to these types.

## Requirement

In MCP 2026-07-28, sampling, elicitation, and roots responses are input responses, not results, and accept only the fields their types define.

## Details

**Rule ID:** `mcp.input-response.closed`  
**Owner:** mcp  
**Surface:** InputResponse  
**Kind:** structural  
**Requirement level:** must  
**Status:** internal · **Enforcement:** internal

## Protocol version applicability

| 2024-11-05     | 2025-03-26     | 2025-06-18     | 2025-11-25     | 2026-07-28 |
| -------------- | -------------- | -------------- | -------------- | ---------- |
| not-applicable | not-applicable | not-applicable | not-applicable | applies    |

## Required by

* **MCP Description 0.9.0, Sections 3.6 and 9.4**  
  * 3\. Document Structure: [req-carried-closed-reject](https://mcpdesc.org/docs/specification/0.9.0-rc.3/document-structure#req-carried-closed-reject)
  * 1. Tools: [req-interaction-protocol-version-valid](https://mcpdesc.org/docs/specification/0.9.0-rc.3/tools#req-interaction-protocol-version-valid)

## Based on

* **Tier 1 — MCP schema.ts and normative specification text:** MCP 2026-07-28 schema.ts, type InputResponse (CreateMessageResult, ListRootsResult, ElicitResult); none extends Result; only CreateMessageResult defines \_meta, through SamplingMessage  
  * [validation/mcp-schemas/2026-07-28/schema.ts#L541-L542](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/dae694f61a31f7a3ec2af3aff709e11f70f61e48/schema/2026-07-28/schema.ts#L541-L542)
  * [validation/mcp-schemas/2026-07-28/schema.ts#L2190-L2228](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/dae694f61a31f7a3ec2af3aff709e11f70f61e48/schema/2026-07-28/schema.ts#L2190-L2228)
  * [validation/mcp-schemas/2026-07-28/schema.ts#L3120-L3149](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/dae694f61a31f7a3ec2af3aff709e11f70f61e48/schema/2026-07-28/schema.ts#L3120-L3149)
  * [validation/mcp-schemas/2026-07-28/schema.ts#L2725-L2744](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/dae694f61a31f7a3ec2af3aff709e11f70f61e48/schema/2026-07-28/schema.ts#L2725-L2744)

## Examples

### Invalid example

Source: [expected-invalid/closed-step-responses-2026.json](https://github.com/mcpdesc/mcpdesc-specification/blob/v0.9.0-rc.3/spec/draft/fixtures/expected-invalid/closed-step-responses-2026.json) · Selected: `/tools/0/interactionExamples/approved/steps/0/response`

```json
{
  "roots": [
    {
      "uri": "file:///workspace/example"
    }
  ],
  "_meta": {
    "trace": "r1"
  }
}
```

## Rule Source Code

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