Feature: Allow disabling specific built-in tools to reduce context overhead

[Lumos-789]

Problem

Claude Code loads ~30 built-in system tools at startup, consuming approximately 16,000+ tokens (8% of a 200K context window) before any conversation begins. This is fixed overhead that cannot be configured.

Many of these tools are unused by specific users/workflows:

• NotebookEdit — irrelevant for non-Jupyter users
• EnterWorktree / ExitWorktree — git worktree users are a minority
• CronCreate / CronDelete / CronList / ScheduleWakeup — scheduling tools rarely used
• ListMcpResourcesTool / ReadMcpResourceTool — MCP resource browsing rarely needed
• TaskCreate / TaskUpdate / TaskList / TaskGet / TaskOutput / TaskStop — task management used by some, not all

Proposal

Add a disabledTools configuration option in settings.json:

{
  "disabledTools": [
    "NotebookEdit",
    "EnterWorktree",
    "ExitWorktree",
    "CronCreate",
    "CronDelete",
    "CronList",
    "ScheduleWakeup",
    "ListMcpResourcesTool",
    "ReadMcpResourceTool"
  ]
}

Disabled tools would not have their JSON Schema definitions loaded into the system prompt, saving 2,000-4,000+ tokens per conversation turn.

Impact

• Token savings: ~2-4K tokens per turn. Over a 50-turn conversation, that is 100K-200K tokens saved.
• Cost savings: At $5/M input tokens (Opus), disabling 5 unused tools saves ~$0.50-1.00 per long conversation.
• Attention quality: Fewer tool definitions means less context dilution and better instruction adherence (per "Lost in the Middle" research).
• Zero risk: Only hides tools the user explicitly opts out of. No behavior change for users who don not configure this.

Alternative Considered

MCP servers are already configurable (add/remove per project scope). Built-in tools should have similar opt-out capability for parity.

Environment

• Claude Code version: latest
• Model: glm-5.1
• OS: macOS Darwin 25.4.0

[NielsFestjens]

You can add them to "permissions" "deny" and then they will not be added to the context.
You can also add tools from MCPs here so you only get the ones you actually use.

[Lumos-789]

worked, many thanks~

[github-actions]

Closing for now — inactive for too long. Please open a new issue if this is still relevant.