cursor-mcp-bridge

cursor-mcp-bridge

MCP server that lets any agent or MCP host delegate to headless Codex, Grok, and Claude Code CLIs, with Cursor available as an opt-in fallback. Use the fleet for implementation, planning, and project exploration without burning the caller's context on raw worker output.

Worker tools take optional model and effort overrides, return a session_id, and support follow_up. Difficulty levels select a distinct default model across the three active subscriptions.

Tools

The server exposes ten tools:

| Tool | Purpose | |------|---------| | delegate | Run a task with full read/edit/shell access in cwd. Required level: 1=GPT-5.6 Luna (codex), 2=Grok 4.5 medium (grok), 3=GPT-5.6 Terra medium (codex), 4=GPT-5.6 Sol medium (codex), 5=Opus (claude). Optionally accepts an agent persona by name or inline {prompt}. | | explore | Read-only exploration on Codex with gpt-5.6-luna. question alone → broad fan-out search returning file:line refs; question+files → answer about those files; neither → general project map. breadth: "thorough" sweeps wider. Locates, does not review. | | read_slice | Surgical read-only read: returns ONLY the code relevant to want (exact lines with file:line) from the given files — the full file never enters your context. Use instead of reading large files whole. | | run_filtered | Run a shell command through Codex/Luna with full access and get back ONLY the lines relevant to want — semantic filtering of huge build/test/log output. | | web_lookup | Web/docs lookup through Codex/Luna with real web search enabled and a read-only filesystem. | | generate_image | Generate or edit an image through Codex's built-in image tool and save it inside cwd. | | plan | Phase 1: read the codebase and return an implementation plan without editing. Defaults to level 4 (Codex Sol, hard read-only); level 5 Claude is read-only by prompt only. | | build | Phase 2: implement an approved plan with full access. Defaults to level 1 (Codex Luna) and optionally accepts an agent persona. | | follow_up | Continue a prior session by session_id. | | bridge_stats | Report calls and chars returned to context per tool (needs CURSOR_BRIDGE_LOG). |

Worker tools accept cwd, model, and effort where applicable. delegate requires a level (1-5); plan and build default to levels 4 and 1 respectively. Explicit model/effort values override the selected tier.

Requirements

• Node ≥ 18
• Codex installed and authenticated for read tools and levels 1/3/4; Grok for level 2; Claude Code

for level 5.

• Optional Cursor fallback: install cursor-agent and set CURSOR_BRIDGE_ENABLE_CURSOR=1.

Install

Installing via an AI agent? Point it at INSTALL.md — an agent-facing, copy-paste guide that detects the host and registers the bridge in Claude Code, Cursor, Codex, Grok, or any generic MCP host.

git clone https://github.com/JaimeJunr/cursor-mcp-bridge.git
cd cursor-mcp-bridge
npm install
npm run build

Register in an MCP host

Claude Code: ``bash claude mcp add cursor-bridge -s user -- node /abs/path/to/cursor-mcp-bridge/dist/index.js ``

Any host — add to its mcp.json: ``json { "mcpServers": { "cursor-bridge": { "command": "node", "args": ["/abs/path/to/cursor-mcp-bridge/dist/index.js"] } } } ``

Permissions (Claude Code): claude mcp add registers the server but does not grant tool permission — without an allowlist every bridge call prompts for approval. After registering, add either "mcp__cursor-bridge__*" (full; also auto-approves mutating tools delegate/build/run_filtered/follow_up) or a read-only subset (explore/read_slice/web_lookup/plan/bridge_stats) under permissions.allow in settings.json. Full options and trade-offs: INSTALL.md §3. Cursor/Codex/other hosts have their own approval settings — consult the host.

Configuration (env)

| Var | Default | Meaning | |-----|---------|---------| | CURSOR_BIN | cursor-agent | Path to the optional Cursor CLI fallback. | | CURSOR_BRIDGE_GROK_BIN | grok | Path to the Grok CLI. | | CURSOR_BRIDGE_CODEX_BIN | codex | Path to the Codex CLI. | | CURSOR_BRIDGE_CLAUDE_BIN | claude | Path to the Claude Code CLI. | | CURSOR_BRIDGE_ENABLE_CURSOR | _(off)_ | Set to 1/true to allow Cursor fallback when a tier's preferred CLI is missing. Otherwise the call fails with the missing CLI named. | | CURSOR_BRIDGE_MODEL | composer-2.5-fast | Default model for the optional Cursor path. | | CURSOR_BRIDGE_EXPLORE_MODEL | gpt-5.6-luna | Codex model for explore, read_slice, run_filtered, and web_lookup when the call omits model. | | CURSOR_BRIDGE_AGENT_PATHS | _(off)_ | Additional :-separated roots for named agent personas, searched before project/home .claude/agents and ~/.claude/plugins. | | CURSOR_BRIDGE_SANDBOX | bwrap | Isolates every engine in a bubblewrap sandbox with an empty $HOME, preventing global config, MCP servers, hooks, and skills from loading. Only auth, required engine state, and toolchains are bound in. Set off/0 to disable; falls back to unsandboxed if bwrap is missing. | | CURSOR_BRIDGE_FORCE | _(off)_ | If 1/true, force-enable non-interactive approval for Cursor and Claude runs. | | CURSOR_BRIDGE_TIMEOUT_MS | 1800000 (30 min) | Per-call safety-net timeout (not a work budget). Execution tools (delegate/plan/build) also get a prompt note so the worker returns partial results before being killed. | | CURSOR_BRIDGE_LOG | _(off)_ | Path to a JSONL file; when set, every call logs {tool, outChars} for bridge_stats. | | CURSOR_BRIDGE_HOOK_MODE | redirect | Hook behavior: off (no-op), nudge (non-blocking additionalContext only), or redirect (deny once + name bridge tool for WebSearch/WebFetch and whole-file large Read; fail-open on retry). Grep/Glob/Bash/Edit/Write stay nudge-only. | | CURSOR_BRIDGE_HOOK_MIN_LINES | 300 | Line threshold above which the optional hook (below) redirects/nudges whole-file Read toward read_slice. |

Security: delegate, build, and run_filtered have full access and auto-approve their work. explore, read_slice, and web_lookup use Codex's read-only sandbox. plan is hard read-only on Codex; level 5 Claude enforces read-only through its prompt. Named agents are resolved on the host, reject path traversal, and are injected without mounting agent directories.

Make the agent actually use it

Registering the tools is not enough. Two structural forces push the agent back to native tools: (1) the host rule "prefer the dedicated file/search tools", and (2) MCP tools used to be deferred — the agent had to run a tool-search to load their schemas, so always-loaded Read/Grep/WebSearch won by default. The server now publishes startup instructions (routing boundary) and marks the five core tools with _meta: { "anthropic/alwaysLoad": true } (Claude Code ≥2.1.121) so their schemas load eagerly; secondary tools stay deferred. Four fixes, strongest first:

1. Call-time hook (recommended). A PreToolUse hook that steers the agent toward the bridge at the moment it reaches for a native tool — text in a config file loses under pressure, a call-time reminder does not. This repo ships one at hooks/prefer-cursor-bridge.mjs: it runs on node (already required) and only fires where it pays. Default mode is redirect (CURSOR_BRIDGE_HOOK_MODE=redirect): for the two safe-to-block cases it returns permissionDecision: "deny" once and names the bridge tool; other cases stay non-blocking nudges. Wire it into your host's settings (Claude Code settings.json):

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Read|Grep|Glob|WebSearch|WebFetch|Bash|Edit|Write|MultiEdit",
        "hooks": [
          { "type": "command", "command": "node /abs/path/to/cursor-mcp-bridge/hooks/prefer-cursor-bridge.mjs", "timeout": 5 }
        ]
      }
    ]
  }
}

What it emits, and when — each fires at most once per session (deduplicated in a tmp file keyed by session_id), because a repeated fire is worse than none: the agent learns to ignore it and every fire costs tokens. Dedup keys are saved before emitting so redirect is one-shot and fail-open (a second identical call is allowed through).

- Read whole-file (no offset/limit) over CURSOR_BRIDGE_HOOK_MIN_LINES lines → redirect (default) or nudge toward read_slice (once per file). Partial reads are left alone. - WebSearch/WebFetch → redirect (default) or nudge toward web_lookup (once). - Grep/Glob → emits the one-time preload reminder to run the ToolSearch for any still-deferred bridge tools (nudge only — never redirected). The dedup collapses them to a single fire. - Bash whose command writes an artifact (git commit/push, git worktree add, gh pr create, gh issue create, bkt pr create) → suggests offloading that grunt-work to delegate (once, nudge only). Read-only Bash (status/diff/log/checkout) is left alone — the orchestrator needs that state, and a mechanical filter (e.g. rtk) already trims the noise. - Edit/Write/MultiEdit → once per session, reminds that a self-contained task (feature, bugfix, mechanical multi-file change, build fix) can go whole to delegate(prompt, level) — the selected worker edits with full access — instead of the orchestrator implementing it on expensive tokens. It never blocks the edit (nudge only); the once-per-session dedup means the orchestrator still edits inline freely (the nudge repositions execution, it doesn't police every edit). - The first qualifying fire of the session (whichever tool triggers it) also carries that preload reminder, so secondary schemas get loaded even in a Read-only or web-only session. - Redirect deny reasons end with a fail-open suffix: if the bridge tool isn't loaded yet, run ToolSearch first; if the native tool is genuinely needed, call it again and it will be allowed (critical under headless -p so the agent never hard-stalls).

Set CURSOR_BRIDGE_HOOK_MODE=nudge for the old non-blocking behavior, or off to disable. To reset the dedup and see the fires again, start a new session (or delete cursor-bridge-nudged-<session_id>.json from your OS temp dir — os.tmpdir(), e.g. /tmp on Linux, not necessarily $TMPDIR).

Preloading at session start (SessionStart)

The PreToolUse preload above only fires when the agent uses the Grep/Read tool. But under pressure agents often reach for Bash grep instead, which matches no PreToolUse matcher — so the preload reminder never arrives. Wire the same hook for SessionStart to close that hole: the preload reminder then lands in context before the first tool decision, regardless of how the agent searches.

{
  "hooks": {
    "SessionStart": [
      { "hooks": [{ "type": "command", "command": "node /abs/path/to/cursor-mcp-bridge/hooks/prefer-cursor-bridge.mjs", "timeout": 5 }] }
    ]
  }
}

On SessionStart the hook emits the ToolSearch preload as additionalContext and pre-marks preload as seen in the session's dedup file, so the PreToolUse piggyback never repeats it.

Reaching subagents too (SubagentStart)

The nudges above only steer the main loop. Spawned subagents never see them, so wire the same hook for SubagentStart as well:

{
  "hooks": {
    "SubagentStart": [
      {
        "hooks": [
          { "type": "command", "command": "node /abs/path/to/cursor-mcp-bridge/hooks/prefer-cursor-bridge.mjs" }
        ]
      }
    ]
  }
}

On SubagentStart the hook injects a compact cursor-bridge preference into every spawned subagent via additionalContext (subagentStartContext(agent_type)). When agent_type is Explore it appends an extra line: that Explore run was spawned on the orchestrator's expensive model (Explore inherits the session model, capped at Opus), so it should route all reading through explore/read_slice (which run on Codex Luna) and keep the expensive shell to orchestration only.

Coexisting with context-mode. The bridge and context-mode use separate channels (context-mode may still do its own thing; this hook only emits additionalContext), so they coexist cleanly — no updatedInput race, no delay, no import of context-mode's routing.

2. Preload any still-deferred tools. The five core tools are already alwaysLoad on Claude Code ≥2.1.121. For secondary tools (or older hosts), tell the agent to load schemas once per session. Add to your CLAUDE.md/AGENTS.md:

At the start of any session involving code reading/exploration, run tool-search once for
`read_slice, explore, run_filtered, web_lookup` (and any secondary bridge tools you need) so
their schemas are loaded if the host still defers them.

3. Reconcile the conflict in CLAUDE.md. State the precedence explicitly:

The host rule "prefer dedicated file/search tools" applies to the EDIT path (Edit needs the
file content → native Read). For PURE reading/locating/web (no edit), cursor-bridge takes
precedence over native Read/Grep/Glob/WebSearch/WebFetch. Read a large file whole with native
Read ONLY when you are about to edit it.

4. Delegate execution, not just exploration. The bridge is not only for reading — delegate runs implementation work with full read/edit/shell access, so the orchestrator shouldn't burn its own tokens on self-contained tasks. State this in CLAUDE.md so the agent routes doing, not just finding, to the cheap worker:

You are the ORCHESTRATOR. delegate(prompt, level) is the DEFAULT for BOTH execution AND judgment.
`level` picks a distinct tier: 1=GPT-5.6 Luna (codex), 2=Grok 4.5 medium, 3=GPT-5.6 Terra medium
(codex), 4=GPT-5.6 Sol medium (codex), 5=Opus (claude). The worker has full read/edit/shell access
in cwd when you delegate. The constant win is context economy: the worker's raw output never enters
your context. Delegate it, then review the result; edit inline only for a quick one-off you're
already positioned for. Use plan(task) then build(plan) when you want a strong read-only planning
phase followed by a cheaper executor. Pass agent:"name" or agent:{prompt:"..."} when the worker
needs a specialized persona.

Develop

npm test       # vitest — unit tests for model resolution / arg building
npm run dev    # run from source via tsx

License

MIT