# Reported issues for next-devtools-mcp

Pod holds 20 of 26 problems reported by people outside the maintainer team. Issues filed by the project's own owners, members and collaborators are excluded entirely — a maintainer's release checklist is not a warning to a prospective user.

Back to [next-devtools-mcp](/mcp/next-devtools-mcp).

## Most discussed

### nextjs_call fails with 'Expected object, received string' when MCP clients serialize args as JSON string

## Bug Description

The `nextjs_call` tool fails with a Zod validation error when MCP clients pass the `args` parameter as a serialized JSON string instead of a parsed object. This is a known pattern across the MCP ecosystem where certain clients serialize object-typed parameters before sending them to the server.

**Error:**
```
Expected object, received string
```

The `nextjs_index` (action: `discover_servers` and `list_tools`) works correctly. Only `nextjs_call` (action: `call_tool`) fails b

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/132) · 2026-04-14 · closed · external user · 2 comments

### Issues with `nextjs_docs` and `nextjs-docs://llms-index`

I'm having issues where the model (in this case, GPT 5.2 Codex in OpenCode) complains it can't get the Next.js docs index or llms-index. Here's the output:

<details><summary>Details</summary>
<p>

> Thinking: Attempting to access Next.js docs  
> I’m trying to read the required nextjs-docs://llms-index resource via the read tool to comply with documentation access requirements, but previous attempts failed; I’ll retry
> reading it directly to resolve this blocker before proceeding.

> → Read ne

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/119) · 2026-01-29 · open · external user · 2 comments

### Codex goes idle after `next-devtools.init`

I have this in my AGENTS.md:

```
**Next.js Initialization**: When starting work on a Next.js project, automatically
call the `init` tool from the next-devtools-mcp server FIRST. This establishes
proper context and ensures all Next.js queries use official documentation.
```

For every new session, Codex runs `next-devtools.init` then goes idle with the message "Initialization complete." – because that's what it's told to do – and I have to respond with "Continue" or something like that. Every. S

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/109) · 2025-12-20 · closed · external user · 3 comments

### Bun Runtime

Hi, 
Can you please add the bun runtime availability that will be helpful, thank you.

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/100) · 2025-12-04 · closed · external user · 7 comments

### [Bug] Auto-discovery fails on Windows - discover_servers returns 406 due to missing Accept header

Environment

  Operating System:
  - Windows 11 (MINGW64_NT-10.0-26200)

  Versions:
  - next-devtools-mcp: 0.3.3 (latest)
  - Next.js: 16.0.3
  - Node.js: v24.9.0
  - Bun: 1.3.0 (used as package manager)
  - React: 19.2.0

  MCP Configuration (.mcp.json):
  {
    "servers": {
      "next-devtools": {
        "type": "stdio",
        "command": "bunx",
        "args": ["next-devtools-mcp@latest"],
        "env": {}
      }
    }
  }

  Next.js Configuration:
  const nextConfig: NextConfig = {
  

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/90) · 2025-11-18 · closed · external user · 5 comments

### MCP Discovery Failure on Windows with Cursor (Next.js 16)

## MCP Discovery Failure on Windows (Next.js 16)

- **Environment**
  - Windows 11
  - Node.js v25.0.0. (tried on v20 too)
  - Node/npm per `next dev`
  - `next@16.0.0`
  - `next-devtools-mcp@^0.2.1`
  - `.cursor/mcp.json` includes `next-devtools` and `Sentry` entries

- **Steps Taken**
  - Install project dependencies (`npm install`)
  - Start dev server: `npm run dev`
    - App reachable at `http://localhost:3000`
    - MCP endpoint responds (requires `Accept: text/event-stream`)
      - Power

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/56) · 2025-10-23 · closed · external user · 6 comments

### CLI: `code --add-mcp <json>` strips quotes when invoked from PowerShell on Windows

# CLI: `code --add-mcp <json>` loses quotes when invoked from PowerShell (Windows)

## Summary

Invoking `code --add-mcp '<json>'` from PowerShell (pwsh) causes the JSON double-quotes to be stripped or mangled, leading to JSON parse errors. Running the VS Code CLI implementation (`cli.js`) directly with `node` succeeds, which suggests the issue is in the PowerShell → cmd handoff or the `code` wrapper's argument handling.

---

## Environment

- OS: Windows 11 Pro (Edition: Windows 11 Pro, Versio

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/55) · 2025-10-23 · closed · external user · 2 comments

### Claude code `failed connection`

I'm adding the MCP using this command 

`claude mcp add next-devtools npx next-devtools-mcp@latest`

latest claude version, cli and vscode extension but still failed connection with the MCP :/

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/52) · 2025-10-22 · closed · external user · 2 comments

## Most recent

### browser_eval wrapper uses outdated field names: ref / startRef / endRef / selector — type, click, drag, evaluate, and fill_form all fail

## Summary

The `browser_eval` action wrapper in `dist/tools/browser-eval.js` sends parameter names that no longer match `@playwright/mcp`'s tool schemas. As a result, `type`, `click`, `evaluate`, `drag`, and `fill_form` all return InputValidationError. Only `start`, `navigate`, `screenshot`, `console_messages`, `list_tools`, and `close` work.

The bug is the same class as #94 / #98 (Playwright MCP renamed `browser_screenshot` to `browser_take_screenshot`), but for several other tools.

## Versi

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/136) · 2026-05-15 · closed · external user · 0 comments

### Docs: warn that NEXT_DEVTOOLS_HOST env var can redirect MCP off localhost

`NEXT_DEVTOOLS_HOST` silently overrides the `localhost` default in [`src/_internal/nextjs-runtime-manager.ts:39`](https://github.com/vercel/next-devtools-mcp/blob/main/src/_internal/nextjs-runtime-manager.ts#L39):

```ts
const MCP_HOST = process.env.NEXT_DEVTOOLS_HOST ?? "localhost"
```

…and is used to construct the fetch target at lines 68 and 306. But the README (checked in v0.3.10 and at HEAD on the default branch) has zero mentions of `NEXT_DEVTOOLS_HOST`, so nothing warns a developer that 

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/133) · 2026-04-21 · closed · external user · 0 comments

### Gives warning on Windows 11

When working in Windows 11 inside Git Bash this MCP server gives the following warning for Claude Code:

`[Warning] [next-devtools] mcpServers.next-devtools: Windows requires 'cmd /c' wrapper to execute npx`

The same seems to be the cause of Claude Code not being able to auto-discover other MCP servers.

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/130) · 2026-04-04 · open · external user · 0 comments

### MCP server failed on exit

* Claude Code v2.1.71
  * No `statusLine` configured
* next-devtools-mcp 0.3.10
* next 16.1.6
* macOS Sequoia 15.7.4
* Apple M1 Pro

Everything works correctly. Claude reports (`/mcp`)

> next-devtools · :heavy_check_mark: connected

After prompting to make sure, Claude reports

> The ... dev server is running on port 4200, and the next-devtools MCP connected successfully.

However when exiting Claude (e.g. with `/exit`), it consistently reports

> 1 MCP server failed

With this being the only M

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/126) · 2026-03-09 · closed · external user · 0 comments

### Dependency security risk - Anthropic's MCP TypeScript SDK has a ReDoS vulnerability

Dependency security risk - Anthropic's MCP TypeScript SDK has a ReDoS vulnerability

@modelcontextprotocol/sdk < v1.25.2 affected
patched version v1.25.2 and higher

Impact
A ReDoS vulnerability in the UriTemplate class allows attackers to cause denial of service. The partToRegExp() function generates a regex pattern with nested quantifiers (([^/]+(?:,[^/]+)*)) for exploded template variables (e.g., {/id*}, {?tags*}), causing catastrophic backtracking on malicious input.

Who is affected: MCP 

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/124) · 2026-02-18 · closed · external user · 1 comment

### Chromium Support

If working on linux arm64, the only chrome browser build is chromium. Any plans on supporting chromium?

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/123) · 2026-02-10 · closed · external user · 0 comments

### Security: next-devtools-mcp pins vulnerable undici (GHSA-g9mf-h72j-4rw9)

## Problem
`next-devtools-mcp` depends on a vulnerable version of `undici` flagged by `npm audit`.

Advisory: GHSA-g9mf-h72j-4rw9
Undici has an unbounded decompression chain in HTTP responses on Node.js Fetch API via Content-Encoding (resource exhaustion).

`npm audit` reports:
- undici 7.0.0 - 7.18.1: moderate severity
- next-devtools-mcp depends on vulnerable versions of undici

## Current versions (from lockfile)
- next-devtools-mcp: 0.3.10
- undici: 7.16.0 (pinned as a direct dependency of n

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/120) · 2026-02-06 · closed · external user · 0 comments

### CVE-2026-0621

There's a [security vulnerability](https://github.com/modelcontextprotocol/typescript-sdk/issues/965) introduced by **@modelcontextprotocol/sdk** 

Affected versions: < 1.25.2
[Patched](https://github.com/modelcontextprotocol/typescript-sdk/pull/1365) version: [1.25.2](https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/v1.25.2)

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/114) · 2026-01-09 · closed · external user · 0 comments

### Won't calling `process.exit(0)` in browser-eval-manager cause a bug?

`src/_internal/browser-eval-manager.ts`

```ts
// browser-eval-manager.ts
process.on("SIGINT", async () => {
await stopBrowserEvalMCP()
process.exit(0) <--- this part
})

process.on("SIGTERM", async () => {
await stopBrowserEvalMCP()
process.exit(0) <--- this part
})
```

Won't telemetry data be lost if I exit immediately?

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/113) · 2026-01-09 · open · outside contributor · 0 comments

### Playwright `screenshot` tool fills context window

The Playwright `screenshot` tool seems to fill the model's context window with base64-encoded image data. Could this data be omitted from the tool response, with the model directed to just read the screenshot image file? 

```
⏺ next-devtools - browser_eval (MCP)(action: "screenshot")
  ⎿  ⚠ Large MCP response (~25.1k tokens), this can fill up context quickly         
  ⎿ {"success":true,"action":"screenshot","result":{"content":[{"type":"text","text"
    :"### Result\nTook the viewport screensh

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/104) · 2025-12-09 · closed · outside contributor · 0 comments

### CVE-2025-66414

https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-w48q-cv73-mx4w

Transitive dependency @modelcontextprotocol/sdk 1.21.0 is introduced via
> next-devtools-mcp 0.3.6  @modelcontextprotocol/sdk 1.21.0

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/103) · 2025-12-09 · closed · external user · 0 comments

### nextjs_index can’t find dev server in Codex CLI even though Next 16 MCP endpoint is reachable

I’m trying to use next-devtools-mcp from the Codex CLI and running into a situation where nextjs_index reports no dev servers, even though:

a Next.js 16 dev server is running and healthy, and
the MCP endpoint at /_next/mcp is reachable from the same environment.
This exact project works with Next DevTools in GitHub Copilot; the problem only appears when using the MCP server via Codex.

Environment

Host: Windows 11 + WSL2
MCP client: Codex CLI (running inside WSL/Ubuntu)
Project: Next.js 16 app

[Read the thread](https://github.com/vercel/next-devtools-mcp/issues/99) · 2025-12-01 · closed · external user · 0 comments

The remaining reports are on [the project's issue tracker](https://github.com/vercel/next-devtools-mcp/issues).