A defense layer for AI coding agents

Detect · Block · Notify — a defense and monitoring layer for AI coding agents.

Your coding agent has full shell access. One prompt injection in a GitHub issue, one hallucinated rm -rf, one MCP tool response that isn't what it claims to be — and it's not a bug report anymore, it's your .env in a stranger's webhook or your home directory gone.

Belay is an open-source, local-first security layer that gates every tool call an AI coding agent makes — blocking destructive commands, secret leaks, and dangerous MCP tool calls in under 100ms, with no LLM in the decision path, no cloud round-trip, and no phone-home by default.

It auto-detects the agents you already run, blocks dangerous actions outright, escalates ambiguous-but-risky ones to you for a one-tap Allow / Deny (in the terminal, the desktop app, or your phone), and notifies you when something happens.

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What it stops

• Secret exfiltration — .env files, API keys, SSH keys, and credentials belonging to other AI tools on the same machine
• Destructive commands — rm -rf /, curl … | sh, fetch→chmod→exec droppers — including common evasion shapes (wrapper prefixes, compound chaining, heredocs, split/long flags)
• Reverse shells and command-and-control egress
• MCP tool-response injection markers — flags embedded "ignore previous instructions"-style content in a tool's response, correlated with any secret-holding session that follows
• Supply-chain, persistence, privilege-escalation, and recon patterns
• Malicious agent skills — install-time gating plus ongoing drift detection, so a skill that's benign at approval time and swapped later gets re-caught

Every rule is tagged with the OWASP Top 10 for Agentic Applications (from OWASP's Agentic Security Initiative), OWASP LLM Top 10, and MITRE ATLAS, and the static scanner emits SARIF 2.1.0 straight into your CI's code-scanning tab.

Known limitation, stated plainly: command-gate detection is pattern-based, not a full sandbox — an interpreter-wrapped call that never surfaces a recognizable shell substring (e.g. a destructive action expressed purely through a scripting language's own API) can still slip through, and a bare network call to a cloud metadata endpoint outside a skill's context isn't yet a dedicated command-gate rule. Belay is defense-in-depth, not a guarantee.

Supported agents

Most agent-safety tools protect one agent. Belay auto-detects and correctly instruments 11 — using the right native mechanism per agent, not a generic shim:

Agent	Interception
Claude Code	native hook
Codex	native hook
Cursor	native hook
Hermes	native hook
OpenClaw	exec policy
Gemini CLI	config policy
Goose	config policy
Cline	MCP proxy
Roo	MCP proxy
Antigravity	MCP proxy
Opencode	plugin

More agents land regularly — run belay detect to check yours, and see MCP proxy below for wrapping any MCP server Belay doesn't natively recognize yet.

Approve from your phone

Step away from your laptop — when a call is an Ask, Belay can send the prompt to a chat app and take your Allow/Deny reply back. Two-way on Telegram, Discord, WhatsApp, Matrix, Mattermost, and Slack; notify-only on ntfy, Teams, WeCom, and webhooks. Enrolment is a one-time pairing code, and it's default-deny — only enrolled approvers can approve, and a prompt that goes stale is auto-denied, never auto-allowed.

How it works

detect  →  protect  →  serve / desktop app
  │           │              │
  │           │              └─ live status, triage, and Allow/Deny in the desktop UI
  │           └─ gate every tool call: Deny > Ask > Allow (fail-closed)
  └─ find the AI agents installed on this machine

Belay gates each tool call deterministically. A Deny can never be downgraded by the dev-toolchain allowlist; an Ask waits for a human decision and denies on timeout. Run with --observe first to tune in log-only mode before enforcing.

How Belay is different

• Broader than a command blocklist. Tools that only block destructive shell commands don't cover secret exfiltration, MCP tool-call abuse, malicious agent skills, or host-level egress. Belay gates all of them from one rule catalog.
• Gates the tool call, not just the shell. Belay sits at the agent's tool-call boundary across native hooks (Claude Code, Codex, Cursor, Hermes), config policy (Gemini, Goose), and an MCP proxy (any MCP server) — not one integration surface.
• Local-first, not a SaaS. No cloud dependency, no LLM in the decision path, no phone-home by default, self-hostable, and the AGPL-3.0 source is yours to read end to end — inspect exactly what it does before you trust it with shell access.

Features

• Runtime gating at the tool-call boundary — native hooks for Claude Code, Codex, Cursor, and Hermes; config-policy for Gemini and Goose; exec-policy for OpenClaw. PostToolUse redacts secret-shaped strings from tool output.
• MCP proxy (mcp-proxy) — wrap any MCP server so every tools/call is gated; fail-closed. Also scans tool responses for embedded injection markers and alerts, correlated against any secret-holding session.
• Deterministic rule catalog — secrets, egress, destructive, RCE, supply-chain, persistence, priv-esc, recon, config-tamper, plus arm→sink and "lethal-trifecta" session correlation.
• Skill security scanning — a dedicated scanner for AI-agent skills: prompt-injection, SSRF/cloud-metadata theft, credential snooping, tool-description poisoning, and anti-refusal manipulation, checked at install time and on an ongoing directory watch with content-hash-keyed trust so a skill can't be swapped for something malicious after approval without re-triggering review.
• Human-in-the-loop approvals — Allow / Deny in the terminal, the desktop app, or a chat app (see Approve from your phone); timeout denies.
• Explain & Advise — every verdict carries a plain-English "why is this risky / what to do" explanation. An optional AI explainer (OFF by default, bring-your-own-key: local Ollama or a cloud provider) can add a second opinion. It is advisory only — it never makes or changes a decision, and secrets/paths are redacted before anything is sent.
• Static pre-install scanner (scan) — patterns, AST, taint, YARA, and OSV analyzers with provenance-weighted scoring and SARIF output for CI. An optional --llm cascade can filter false positives; with no API keys it runs fully local and heuristic-only.
• Tamper-evident audit — a hash-chained audit log plus evidence build / evidence verify (SHA-256 manifest over findings + SARIF).
• Honeypot canaries — decoy credential files that trip a Critical verdict on read or egress.
• Host control — a native Rust firewall and a bundled per-ecosystem vulnerability DB, with no external tools and no NVD key required. The vuln DB surfaces CISA KEV (known-exploited) badges and EPSS exploit-probability scores, and outbound destinations can be annotated with reverse-DNS + ASN / owner / country (display-only — never gates).

Install

Linux & macOS (CLI):

curl -fsSL https://dl.belay.secblok.io/install.sh | bash

Windows (desktop app, PowerShell 5.1+):

irm https://dl.belay.secblok.io/install.ps1 | iex

Prefer not to pipe a script for a security tool, understandably — read it first, or grab a direct binary and verify its checksum yourself:

# Read before running
curl -fsSL https://dl.belay.secblok.io/install.sh -o install.sh
less install.sh && bash install.sh

# ...or download a checksummed desktop installer directly
# Windows:      belay-setup-x64.exe
# macOS (arm):  belay-aarch64.dmg     macOS (Intel): belay-x64.dmg
# Linux (.deb): belay-amd64.deb       Linux (AppImage): belay-amd64.AppImage
# https://github.com/SECBLOK/belay/releases/latest

Every download is checked against a published SHA256SUMS/.sha256 before installing, refusing on a mismatch. The Windows and macOS installers are currently unsigned while a code-signing/notarization certificate is pending — Windows SmartScreen and macOS Gatekeeper may warn on first run ("More info → Run anyway" / right-click → Open).

Uninstall anytime with belay uninstall (add --purge to also remove ~/.belay).

Quick start

Once installed, drive Belay with the belay binary already on your PATH (or launch the desktop app, which walks you through the same flow):

# 1. See which agents are installed
belay detect

# 2. Protect one in log-only mode first (tune, no enforcement)
belay protect <agent> --observe

# 3. Enforce
belay protect <agent>

# 4. Run the local backend (the desktop app renders the UI)
belay serve

Review activity with belay status (the last audit rows) and belay logs (a longer tail).

belay serve exposes a local API + SSE backend on 127.0.0.1 — it is not a web dashboard. The desktop app is the user interface. Enable boot-start with belay install-service --enable (systemd / launchd).

Build from source

Contributors can build the single static binary from a checkout:

cargo build --release --bin belay

The primary Linux target is a fully-static musl build (--target x86_64-unknown-linux-musl), which needs the musl toolchain — install musl-tools (Debian/Ubuntu: sudo apt install musl-tools) so musl-gcc is available.

Contributions are welcome — see CONTRIBUTING.md. Contributions require a CLA + DCO sign-off.

Platform support

Platform	CLI	Desktop app
Linux x86_64	Released — fully-static musl build, runs on any libc	Released — .deb / .AppImage
macOS (Intel + Apple Silicon)	Released	Released — .dmg, both architectures
Windows	Released	Released — NSIS installer (unsigned, cert pending)
Linux aarch64	Coming soon	Coming soon

FAQ

How do I stop my AI coding agent from running rm -rf or other destructive commands? Install Belay and run belay protect <agent>. Destructive commands — including common evasion shapes like wrapper prefixes, compound chaining, and heredocs — are denied outright at the tool-call boundary before they execute.

Can an AI agent leak my API keys or .env secrets? Not once protected — Belay's rule catalog denies reads/egress of secret-shaped strings and redacts them from tool output; honeypot canary files trigger a Critical verdict on any access.

Does Belay work with Claude Code, Cursor, Codex, Cline, and Gemini CLI? Yes — see Supported agents for the full list and how each is intercepted.

What's the difference between an AI agent security tool and a network firewall? A firewall controls network traffic; Belay controls what an agent is allowed to do at the tool-call level — reading files, running commands, calling MCP tools — before any of it reaches the OS or network. (Belay also includes a native host firewall as one layer among several — see Features.)

Is there an open-source alternative to a hosted AI-agent-safety SaaS? Yes — Belay's Community edition is AGPL-3.0-or-later, local-first, and self-hostable; no telemetry, no phone-home. See Editions & licensing.

Documentation

Full docs live at https://belay.secblok.io/doc (landing page: https://belay.secblok.io) — guides, the complete CLI reference, and configuration.

Editions & licensing

Belay is open-core.

• Community — everything above, free and open source under AGPL-3.0-or-later.
• Enterprise — a commercial license adds centralized capabilities: fleet management, organizations / multi-tenancy, device management & enrollment, cross-device correlation, SSO (OIDC) + SCIM, a hosted/curated advisory feed (EPSS + CISA-KEV enrichment), audit push, and compliance reporting.

For AGPL-incompatible use or the Enterprise edition, see COMMERCIAL-LICENSE.md or contact [email protected].

Published by SECBLOK (Secblok Pty Ltd) · https://www.secblok.io

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