75trust / 100

Guard Shell

by ShellPermit in Developer tools

x402 APIPassing, checked 1 h ago

Decide whether an agent-authored bash command complies with an execution policy, using a real shell tokenizer rather than pattern matching. Catches recursive deletes, force pushes, cluster and infrastructure teardown, raw device writes, path escapes, privilege escalation, and curl-piped-to-shell through pipelines, substitutions, quoting games and base64. Returns reason codes with spans and an optional short-lived permit bound to the exact canonical command. Never executes anything.

POST
https://shellpermit.schemasure.com/v1/guard/shell
Price
$0.03
per call in USDC
Uptime
100%
last 30 days
Response time
359 ms
475 ms slowest 5%
Last check
Passed
1 h ago, next any minute now

Run a free test callHow to call it

Reliability

All checks passedSome failedAll failedNot checked

Status and outage history · Atom feed · Watch with other listings

How to call it

POST https://shellpermit.schemasure.com/v1/guard/shell

Each call costs $0.03 in USDC on Base, paid with the request over x402.

Run a free test callOne unpaid request, the way an agent sends it. You see the payment challenge it gets back. Nothing is charged.

Example request

From the listing.

POST https://shellpermit.schemasure.com/v1/guard/shell
content-type: application/json

{
  "audience": "executor:acme-prod-01",
  "command": "rm -rf ./dist && npm run build",
  "issue_permit": true,
  "policy": {
    "allow_destructive": true,
    "allow_network_egress": false,
    "allowed_roots": [
      "/srv/app"
    ],
    "cwd": "/srv/app"
  },
  "shell": "bash"
}

Parameters

ParameterTypeRequiredDescription
audiencestringNoIdentity of the ONE executor the permit is for. Required when issue_permit is true. Wildcards are rejected.
commandstringYes
envobjectNoEnvironment the executor will run with, used only for static expansion so that paths like "$HOME/.cache" can be resolved and decided rather than reported as unresolvable.
issue_permitbooleanNo
policyobjectNo
shellstringYesRequired. Only bash is supported in v1: a permit issued under one shell's grammar and executed under another is a parser differential with a signature on it. One of: bash.
subjectstringNoOpaque caller label recorded as the permit subject.

Example response

The provider's example. We can't check it without paying.

{
  "confidence": 1,
  "evidence": [],
  "ok": true,
  "result": {
    "canonical_command": "rm -f -r ./dist && npm run build",
    "cmd_fingerprint": "a1b2c3d4e5f60718",
    "cmd_hash": "sha256:0f4c…1c2d",
    "permit": "eyJhbGciOiJFZDI1NTE5Iiwia2lkIjoi…"
  },
  "risk_codes": [],
  "verdict": "pass",
  "warnings": [
    "cmd_fingerprint is ADVISORY and must not be used for authorization."
  ]
}

Call it from code

The curl command shows the payment challenge. The JavaScript and Python versions pay and call, and never pay more than $0.03.

curl: see the payment challenge
# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://shellpermit.schemasure.com/v1/guard/shell' \
  -H 'content-type: application/json' \
  --data-raw '{"audience":"executor:acme-prod-01","command":"rm -rf ./dist && npm run build","issue_permit":true,"policy":{"allow_destructive":true,"allow_network_egress":false,"allowed_roots":["/srv/app"],"cwd":"/srv/app"},"shell":"bash"}'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - -X POST 'https://shellpermit.schemasure.com/v1/guard/shell' \
  -H 'content-type: application/json' \
  --data-raw '{"audience":"executor:acme-prod-01","command":"rm -rf ./dist && npm run build","issue_permit":true,"policy":{"allow_destructive":true,"allow_network_egress":false,"allowed_roots":["/srv/app"],"cwd":"/srv/app"},"shell":"bash"}' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode
JavaScript: pay and call
// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.03 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.03" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.03 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fshellpermit.schemasure.com%2Fv1%2Fguard%2Fshell&method=POST
const res = await pay("https://shellpermit.schemasure.com/v1/guard/shell", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "audience": "executor:acme-prod-01",
    "command": "rm -rf ./dist && npm run build",
    "issue_permit": true,
    "policy": {
      "allow_destructive": true,
      "allow_network_egress": false,
      "allowed_roots": [
        "/srv/app"
      ],
      "cwd": "/srv/app"
    },
    "shell": "bash"
  }),
});
console.log(res.status, await res.text());
Python: pay and call
# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.03 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.03"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://shellpermit.schemasure.com/v1/guard/shell",
        json={
            "audience": "executor:acme-prod-01",
            "command": "rm -rf ./dist && npm run build",
            "issue_permit": True,
            "policy": {
                "allow_destructive": True,
                "allow_network_egress": False,
                "allowed_roots": [
                    "/srv/app",
                ],
                "cwd": "/srv/app",
            },
            "shell": "bash",
        },
    )
    print(res.status_code, res.text)

Security scan

No findings

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