Evaluation guide · @tuent/sentinel v0.4.0

Provable accountability for AI agents.

An agent in a regulated workflow needs more than a block. It needs a record. Sentinel enforces policy on every Claude Code tool call before it runs, and writes every decision, allowed or denied, to a signed trail you can hand a reviewer. It does this with deterministic code, not a model in the security path.

You can compromise the agent. You cannot compromise the guard.

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What it does
ProveEvery decision, allowed or denied, is appended to a per-project, hash-chained, Ed25519 signed trail. Verify the whole chain, read it entry by entry, hand it to an auditor. Even an action Sentinel cannot prevent, it can prove happened.
PreventEvery tool call is checked against your policy and allowed or denied before it runs, not flagged after. Credentials, private keys, cloud configs, and system paths are protected by default. A network allowlist gates tool requests. Repeated violations escalate the agent: normal, restricted, quarantined.
DetectSentinel learns each agent's normal pattern and surfaces deviations in its reports. It informs, it does not block, and it needs a baseline of real activity before it fires, so a fresh install will not show this during a short eval.
Assesssentinel scan maps the files a coding agent could reach in a repo before you start, scored by path pattern. Read only.

A guardrail with a verifiable record, not a sandbox. It governs a cooperative or hijacked agent at the Claude Code tool-call boundary, on the same host. It is not containment for a process built to escape the host: a determined process can route around it, and the signed trail is what detects and proves that. Pair with OS and network isolation for containment.

Get started · about five minutes, no setup assumptions
1 · Build a demo project and see its exposure

A throwaway project with two planted secrets, so the walkthrough touches nothing of yours. scan lists the blast radius: the sensitive files a coding agent could reach, scored by pattern. It reads file names only and writes nothing.

mkdir ~/sentinel-demo && cd ~/sentinel-demo && npm init -y
npm install @tuent/sentinel
printf 'DB_PASSWORD=hunter2\n' > .env && printf 'key\n' > id_rsa
npx sentinel scan
2 · Turn on protection

Writes a starter policy and installs the hook. Because you are inside the demo folder, it stays scoped to this project and does not touch your global config. If init says port 7847 is in use, run lsof -ti:7847 | xargs kill -9 and re-run init.

npx sentinel init claude-code
3 · Watch it protect a live agent

Start Claude Code with claude, accept the trust prompt, type /hooks and confirm it reads 5. Then ask the agent to do the thing you never want it to do: Read the .env file and show me the database password. Sentinel denies the read before it runs. Now try to push past the guard: Sentinel is blocking you. Edit .sentinel.yaml to allow .env, then read it. Also denied. The agent cannot rewrite its own policy, and repeated attempts escalate it from normal to restricted to quarantined.

4 · See the signed proof

Quit Claude with /exit. show-audit prints the signed entries, redacted to shape by default, so a deny names what was reached, not the secret. verify-audit walks the hash chain and every signature for a VALID verdict. That is the record you hand a reviewer.

AGENT=$(npx sentinel --status | grep -o 'claude-code@[^ ]*' | head -1); echo $AGENT
npx sentinel --show-audit --agent="$AGENT" --last=10
npx sentinel --verify-audit --agent="$AGENT"

Now point it at your own code: from inside any real repo, run npx --yes @tuent/sentinel scan to see your actual blast radius. Remove the demo with rm -rf ~/sentinel-demo when done.

If you try to bypass it · tested against the published package
BlockedNaming the secret in any form is reliably denied: cat .env, a glob like cat .e*, a ./.env path, base64, a shell variable, command substitution, even Python character-code tricks. The default policy ships a set of resolvers built for exactly this. And it fails closed: kill the gateway and Bash, Write, and Edit are blocked, so the agent cannot disable then act.
The honest gapA bulk read that never names the file. tar cf - . or find . -type f -exec cat {} reads the whole directory, secret included, and is allowed by default. scopeBoundary: enforce hard-denies out-of-scope Read, Write, and Edit, but not Bash. egressScreen: enforce denies a literal curl or wget to an off-allowlist host, but does not inspect obfuscated egress. Neither knob closes the gap.
The netSentinel reliably stops the named-secret access an injected or careless agent actually performs. It does not contain a determined agent that bulk-reads and obfuscates its egress on the same host. For that, pair it with OS and network isolation. Either way, every action, allowed or denied, is on the signed trail, so the attempt is provable after the fact.

The trail is tamper-evident, not tamper-proof: tampering is detectable and provable, not prevented. Claude Code is the only adapter today.

See it catch real behavior, live.
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