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ThumbGate MCP Server

Community
Self-improving firewall for AI coding agents that gates tool calls before they run
Category
Dev Tools #108 of 438
Stars
★ 29 Popular
Transport
stdio (local process)
Runtime
Node.js 18+
Credentials
No credential needed
License
MIT
Last commit
Tools
13
61FMRS · C

A thoughtfully engineered local-first gating layer: no LLM on the enforcement path, auditable decisions, break-glass recovery, and honest disclosure of limits. Its value hinges on hook interception — hard enforcement only on PreToolUse-capable agents — and the docs candidly note advisory-mode limits, estimate-based savings, and unshipped roadmap items. Well suited to teams wanting a cross-agent, learning rule store; overkill for simple static denylists.

Strongest · Documentation 14/20 Weakest · Reliability 8/20

Reliability
8/20
Security and permissions
13/20
Maintenance
13/20
Documentation
14/20
Setup experience
13/20
Why each score
Reliability 8/20
server.json clearly declares stdio transport and a fixed launch command (npx -y thumbgate serve), and the README explicitly warns against npm start (which launches the unrelated HTTP API from a sibling service). Beyond that, no tool list, parameter schema, or test evidence specific to this stdio server is provided; the README's CI badge and eval/monitor npm scripts appear to target a separate 'task outcome' subsystem, not proven to cover this server's init/tool-list handshake. Per the static calibration rule, without verifiable execution evidence (CI + committed tests) covering this server's key paths, reliability is capped at 12; given the thin evidence (no tool manifest, no server-specific tests visible), it is scored 8.
Security and permissions 13/20
THUMBGATE_MCP_PROFILE defaults to the least-privilege 'essential' profile, only expanding scope when explicitly set — a good least-privilege signal. The README also candidly discloses that only detected secret leaks and self-disable commands hard-block by default; other high-risk classes (rm -rf, force-push, off-scope edits, deploys) only warn-and-log by default and require THUMBGATE_STRICT_ENFORCEMENT=1 to deny, and for Cursor/Cline/OpenCode the gate_check is merely advisory (the agent can ignore it). This is not a red-line case, since the server itself does not execute the dangerous action — it only renders a verdict on another tool's call — and the limitation is clearly disclosed. Since no source-level tool/permission list could be verified, and there is an external network surface toward thumbgate.ai for licensing/billing, full marks are not warranted.
Maintenance 13/20
The project is MIT-licensed and the npm package is at version 1.36.1, indicating ongoing iteration; the README references a CI badge, a Changesets process, and release-confidence documentation, suggesting some release governance. However, 48 open issues against only 25 stars is a comparatively high ratio that may indicate unresolved backlog or slower responsiveness, and no recent-commit evidence is available. Scored as active but with governance/responsiveness gaps.
Documentation 14/20
The README is extremely thorough, covering install, architecture, CLI reference, built-in checks, recovery flow (break-glass), pricing, and FAQ, and links out to THREAT_MODEL.md, VERIFICATION_EVIDENCE.md, and other docs. However, a large portion is marketing/sales content (pricing tiers, enterprise pitch, SEO landing links) rather than technical reference, and since this repository ships 3 MCP servers, many tool names mentioned in the README (capture_feedback, gate_check, record_task_outcome, etc.) are not clearly attributed to this specific server.json stdio server versus its siblings — there is no formal parameter-level tool reference scoped to this server.
Setup experience 13/20
The manifest specifies a single, clear launch path (npx -y thumbgate serve over stdio), and the README has a dedicated section clarifying the correct MCP/registry install command and warning against a common misconfiguration (npm start launching the wrong HTTP service). This is clear and low-friction. However, per the static calibration rule, without source-verifiable test/CI evidence covering this exact path, setup is capped at 15; within that ceiling it is scored a relatively high but non-maximal 13.

Static review · not runListed 2026-09-07

Read the FMRS scoring method →

Fit and risk

What it can accessReads local filesWrites / deletes local filesRuns commands or code

Best for

  • Developers running AI coding agents in production or high-blast-radius workflows who need an external enforcement boundary
  • Engineering/security/platform teams wanting auditable, inspectable gate decisions
  • Teams converting repeated corrections into reusable rules instead of relying on model memory

Not for

  • Small teams happy with a small static hand-written denylist (native hooks suffice)
  • Those expecting gating to improve model generation quality (it intercepts execution only)
  • Cursor/Cline/OpenCode users handling irreversible actions, since advisory verdicts can be ignored

Required permissions

  • Runs locally over stdio; reads/writes ~/.claude or in-repo .claude config, hooks, and lesson stores
  • Writes local state (.thumbgate/), JSONL logs, and task-outcome receipts
  • Requires modifying the agent's MCP and PreToolUse hook configuration files
  • Task-outcome decisions need THUMBGATE_HUMAN_REVIEWER_ID and an independently revocable human reviewer key

Risks and side effects

  • Advisory integrations (Cursor, Cline, OpenCode, Amp) can be ignored by the agent — no true blocking of irreversible actions
  • In strict mode, false positives from stale or noisy rules can block legitimate work; recovery relies on break-glass
  • Ships warn-by-default: most high-risk commands are not blocked unless strict enforcement is on
  • Dashboard token/dollar savings are estimates, not measured provider usage
  • Lesson DBs contain sensitive engineering context and must stay gitignored in per-project installs
  • Regulated-industry templates are roadmap directions, not shipped compliance capabilities

Setup

Before you start

Runtime:Node.js 18+

Other optional settings (2)
THUMBGATE_MCP_PROFILE optional Optional MCP tool profile override (essential | default | readonly | locked). Omit to keep the factory least-privilege essential profile; only set when expanded tools are intentional.
THUMBGATE_STRICT_ENFORCEMENT optional Set to 1 to preserve deny decisions for every matched blocking rule; by default most matched gates warn and log instead of blocking.

Run npx thumbgate init to auto-detect and wire your agent's integration, or run it as a stdio MCP server directly: npx -y thumbgate serve. Optional THUMBGATE_MCP_PROFILE (essential | default | readonly | locked) overrides the tool profile; THUMBGATE_STRICT_ENFORCEMENT=1 enables strict blocking. Do not use npm start for MCP — that launches the HTTP API, not the stdio server.

.mcp.json
{"mcpServers":{"thumbgate":{"command":"npx","args":["-y","thumbgate","serve"]}}}

Shown for Claude Code. Other clients may use a different file or key (VS Code uses "servers") — the configurator below converts it.

.vscode/mcp.json
{
  "servers": {
    "thumbgate": {
      "command": "npx",
      "args": [
        "-y",
        "thumbgate",
        "serve"
      ]
    }
  }
}

Goes in your project's .vscode/mcp.json (VS Code uses a "servers" key).

Terminal
claude mcp add thumbgate -- npx -y thumbgate serve

Run it in a terminal; replace any <…> placeholders with your own values first.

Check that it works

After configuring the client with {"mcpServers":{"thumbgate":{"command":"npx","args":["-y","thumbgate","serve"]}}}, start the client and confirm the thumbgate server appears with tools such as gate_check and capture_feedback; alternatively run 'npx thumbgate doctor' to health-check the hooks and MCP wiring.

Troubleshooting

  1. Run npx thumbgate doctor to check hooks, MCP wiring, and agent readiness
  2. Ensure you use npx thumbgate serve (stdio), not npm start which starts the HTTP API
  3. Restart the agent session after changing MCP or hook settings so configs reload
  4. If a gate over-fires, use npx thumbgate break-glass --reason=... to open a short recovery window
  5. Verify THUMBGATE_STRICT_ENFORCEMENT and THUMBGATE_MCP_PROFILE environment variables match expectations
  6. For per-project installs, confirm .claude/memory/feedback/ is gitignored

Things to try

Once connected, you can ask your AI assistant things like:

  • Check whether running 'rm -rf tests/' would trigger any prevention rules
  • Capture a thumbs-down lesson: never run DROP on production tables
  • Show me the active prevention rules and lessons guarding this repo
  • What has ThumbGate actually blocked so far? Show gate stats and the enforcement matrix

Tools 13

gate_check read-only
Evaluates a proposed tool call before execution and returns an allow/warn/deny verdict
capture_feedback writes
Captures thumbs-up/down feedback as a structured local lesson
open_feedback_session writes
Opens a feedback session to add context beyond a thumbs-down
append_feedback_context writes
Appends concrete context to an open feedback session
finalize_feedback_session writes
Finalizes the session and infers a lesson from the full conversation
record_task_outcome writes
Records a task-level receipt marked working only with completion, verification, and evidence
search_lessons read-only
Searches the local lesson corpus (Pro capability)
prevention_rules read-only
Lists active prevention rules
Show 5 more tools
get_reliability_rules read-only
Retrieves the reliability rules list
gate_stats read-only
Shows gate blocking statistics
enforcement_matrix read-only
Shows the enforcement matrix of what has actually been blocked
get_branch_governance read-only
Shows branch/release governance status
approve_protected_action writes
Grants a scoped, expiring approval for a protected action

Use cases

Flag or block git push --force to protected branches before it runs
Turn recurring failures (deleted test dirs, production DROPs) into prevention rules
Hard-block detected secret exfiltration by default
Share one local lesson and rule store across multiple agents
Use a 5-minute break-glass window to recover when a gate over-fires

Supported clients

Claude Code
Claude DesktopPartial support
CursorPartial support
Codex
Gemini CLI
ClinePartial support
OpenCodePartial support
AmpPartial support

Listed from the project's documentation, not tested by this site.

Overview

ThumbGate is a local-first Pre-Action Checks engine that runs as a stdio MCP server and via PreToolUse hooks to evaluate proposed AI agent tool calls before execution. It captures thumbs-up/down feedback as local lessons, promotes repeated failures into prevention rules, and hard-blocks detected secret leaks plus direct self-disable commands (process kill, env bypass) by default. Other high-risk classes (rm -rf, force-push, fetch-and-run) warn and log by default; THUMBGATE_STRICT_ENFORCEMENT=1 preserves deny decisions for every matched blocking rule. Gate decisions are deterministic (literal/AST matching with local bge-small embeddings via LanceDB) — no LLM runs on the enforcement path. Claude Code, Codex, and Gemini CLI get hard interception; Cursor, Cline, OpenCode, and Amp get advisory gate_check only. Free tier: 2 feedback captures/day (10 total), 3 active auto-promoted prevention rules; Pro at $19/mo adds unlimited rules, lesson recall/search, and a personal dashboard. MIT-licensed.

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Source revision e088a6d6df56 Data synced 2026-10-19 Read the FMRS scoring method