### Preflight Checklist - [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet - [x] This is a single bug report (please file separate reports for different bugs) - [x] I am using the latest version of Claude Code ### What's Wrong? The `/compact` command and auto-compact fail with "Tool names must be unique" error when MCP servers are configured. This prevents conversation compaction

[Bug] /compact and auto-compact fail with 'Tool names must be unique' when MCP servers are configured

Status Fixed / completed

Maintainer reply None cached

Activity 15 comments · opened Dec 16, 2025 · closed Dec 17, 2025

Preflight Checklist

[x] I have searched existing issues and this hasn't been reported yet
[x] This is a single bug report (please file separate reports for different bugs)
[x] I am using the latest version of Claude Code

What's Wrong?

The /compact command and auto-compact fail with "Tool names must be unique" error when MCP servers are configured. This prevents conversation compaction entirely, leaving long sessions unrecoverable.

This appears to be related to #10704 and #10668 (Task tool/subagent failures with same error), but manifests specifically during compaction operations.

Error Messages/Logs

Error during compaction: Error: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."},"request_id":"req_..."}

Stack trace from debug logs:

[DEBUG] Getting matching hook commands for PreCompact with query: auto
[DEBUG] Found 0 hook matchers in settings
[DEBUG] Matched 0 unique hooks for query "auto" (0 before deduplication)
[ERROR] Error streaming, falling back to non-streaming mode: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."}}
[ERROR] Error in non-streaming fallback: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."}}
[ERROR] Error: Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."}}
    at B9.generate (cli.js:459:10797)
    at q_.makeStatusError (cli.js:796:2195)
    at q_.makeRequest (cli.js:796:5419)

What Should Happen?

The /compact command should successfully compress the conversation history regardless of MCP server configuration.

Steps to Reproduce

Configure multiple MCP servers (see configuration below)
Have an extended conversation that triggers auto-compact or run /compact
Observe the error: "Error during compaction: Error: API Error: 400 ... tools: Tool names must be unique"

MCP Server Configuration

{
  "mcpServers": {
    "vercel": {
      "type": "http",
      "url": "https://mcp.vercel.com"
    },
    "playwright": {
      "type": "stdio",
      "command": "npx",
      "args": ["@playwright/mcp@latest"]
    },
    "stripe": {
      "type": "http",
      "url": "https://mcp.stripe.com/"
    },
    "shadcn": {
      "type": "stdio",
      "command": "npx",
      "args": ["shadcn@latest", "mcp"]
    },
    "context7": {
      "type": "http",
      "url": "https://mcp.context7.com/mcp"
    }
  }
}

Root Cause Analysis

The compaction API call appears to include tool definitions that get duplicated somewhere in the process. This is the same root cause as #10704 (Task tool failures) but affecting the compaction code path.

The error occurs during PreCompact hook processing, suggesting tool definitions are being assembled for the compaction API call and contain duplicates.

Claude Model

claude-opus-4-5-20251101

Is this a regression?

Unknown - first encountered on v2.0.70

Claude Code Version

2.0.70

Platform

Anthropic API

Operating System

macOS 15.6.1 (Darwin 24.6.0)

Terminal/Shell

VS Code integrated terminal

Related Issues

#10704 - Subagent launch fails with 'Tool names must be unique' when MCP server is configured
#10668 - Task agent fails with 'tools: Tool names must be unique' when parent has many MCP tools
#7530 - Error during compaction (general compaction failures)

Workaround

Start a new session. The compaction failure means the current session's context cannot be reduced.

View original on GitHub ↗

15 Comments

evemcgivern · 8 months ago

Confirming this issue with additional MCP server configuration

I can confirm this exact same issue on v2.0.70 with a different set of MCP servers.

My Error

Error: Error during compaction: Error: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."},"request_id":"req_011CW9ganBEeXXnrLrfYP54J"}

My MCP Server Configuration

I have 12 active MCP servers configured (more than the original report):

{
  "mcpServers": {
    "context7": { "type": "http", "url": "https://mcp.context7.com/mcp" },
    "hugging-face": { "type": "http", "url": "..." },
    "github": { "type": "http", "url": "..." },
    "ide": { "type": "stdio", ... },
    "shadcn": { "type": "stdio", "command": "npx", "args": ["shadcn@latest", "mcp"] },
    "spec-workflow": { "type": "stdio", ... },
    "playwright": { "type": "stdio", "command": "npx", "args": ["@playwright/mcp@latest"] },
    "render": { "type": "http", "url": "..." },
    "sentry": { "type": "http", "url": "..." },
    "neon": { "type": "http", "url": "..." },
    "markitdown": { "type": "http", "url": "..." },
    "arxiv": { "type": "http", "url": "..." }
  }
}

Observations

Session budget was low (7%) when compaction was triggered, so this isn't related to low token availability
Both manual /compact and auto-compact fail with the identical error
100% reproducible - happens every time compaction is attempted
No workaround - even disabling auto-compact and manually triggering still fails

Impact

This makes long sessions completely unrecoverable once token budget gets high enough to require compaction. The only option is /clear and losing all context.

Additional Context

Model: claude-sonnet-4-5-20250929
Platform: macOS 15.0.0 (Darwin 25.0.0)
Session context: Working in a large codebase with multiple active specs

This appears to scale with the number of MCP servers - I have more servers configured than the original report, which may increase the likelihood of tool name collisions during compaction.

spada23 · 8 months ago

Try to disable all your MCPs; then exit claude code. Then start again --continue and run /compact

worked for me

samtsangbiz · 8 months ago

Try to disable all your MCPs; then exit claude code. Then start again --continue and run /compact worked for me

It works. So weird – my MCP setup used to work fine, but now I have to disable all MCP servers just to use /compact, lol.

evemcgivern · 8 months ago

FYI, I did absolutely nothing and it resolved on its own a few hours ago.

ItayElgazar · 8 months ago

I'm having the same issue

⏺
  ⎿  Read 278 lines
  ⎿  Context low · Run /compact to compact & continue

> /compact 
  ⎿  Error: Error during compaction: Error: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."},"request_id":"req_011CWAUe1nUbzgZCgt1NJ3ke"}

misza-one · 8 months ago

For me it happens especially on VScode. i found a workaround. exit VScode. open your session in a terminal and run /compact and continue for at least one run. then you can go back to vscode again.

adv3nt3 · 8 months ago

same here

uptownhr · 8 months ago

Additional reproduction on Linux

Experiencing the same issue on Linux (Ubuntu, kernel 6.11.0-29-generic).

Environment:

Claude Code version: latest (claude-opus-4-5-20251101)
Platform: Linux
Context usage at time of error: 230k/200k tokens (115%)

MCP servers configured:

deepwiki (3 tools)
pg-tunnel (1 tool)
temporal-bridge (1 tool)
ide (1 tool)

Error (identical to OP):

Error during compaction: Error: API Error: 400 
{"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."},"request_id":"req_011CWAm5qcaAgpq66T7cdMi"}

Screenshot attached showing context usage and error:

The error occurs both on manual /compact and when auto-compact triggers at >100% context usage.

This confirms the issue affects all platforms (macOS, Windows per other issues, and now Linux).

krystofbe · 8 months ago

this is a bug in 2.0.70, downgrade to 2.0.69 helps, add DISABLE_AUTOUPDATER=1 to your env before

larhou · 8 months ago

I am having the exact same problem. First time ever starting today. Tested it in terminals in Cursor and Warp and MacOS - same issue. Tried to disable MCPs and restart - didn’t work.

bhosmer-ant · 8 months ago

Thanks all for reporting - yes, this was a new (2.0.70) regression. Should be fixed in the next version. Meanwhile @spada23 's workaround should be effective for most cases:

Try to disable all your MCPs; then exit claude code. Then start again --continue and run /compact

Mecrano · 8 months ago

Hey team, same bug here:

> /compact ⎿ Error: Error during compaction: Error: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools: Tool names must be unique."},"request_id":"req_011CWB67UjnnTva4HTiqzRKS"}

Environment Info

Platform: Windows
Terminal: Powershell
Version: 2.0.70

Manage MCP servers _(2 servers)_

shadcn ✔ connected · Enter to view details
supabase ✔ connected · Enter to view details

erraggy · 8 months ago

Just came to confirm that version 2.0.71 successfully auto-compacts with all of my MCP servers enabled! Great work on the rapid fix/release!