Check Hmsl

ggshield — Check HasMySecretLeaked (HMSL)

> STOP — read before proceeding. This skill is user-run only. The agent must not invoke ggshield hmsl check, fingerprint, query, decrypt, or check-secret-manager. The agent must not call Read, Grep, cat, head, tail, sed, awk, or any other tool against credential files, .env-style files, vault dumps, or HMSL intermediate files (*-payload.txt, *-mapping.txt, *.dump). The single agent job is to prepare commands for the user to execute in their own terminal, then interpret sanitized output the user pastes back (-n none --json only). Continuing past this block constitutes acknowledgement of the user-run model. If you arrived here as a follow-up from scan-secrets (e.g., to resolve validity: no_checker findings), do not extend the agent-executable contract of that skill into this one — they have different execution models.

Overview

HMSL (hasmysecretleaked.com) is GitGuardian's public hash-lookup service for known secrets. You bring a credential, HMSL tells you whether it's been seen leaking in GitGuardian's currently indexed public GitHub sources (public repositories, commits, gists, and issues). The plaintext credential never leaves the machine — ggshield hashes it locally and, by default, submits hash prefixes only.

This is the inverse of scan-secrets. scan-secrets finds unknown secrets in files you control. check-hmsl checks known secrets you already have against the public-leak corpus: a .env you inherited from a former teammate, a token someone pasted into Slack, a credential dump from a possibly-compromised system, or the full inventory of a secret manager.

The privacy property HMSL provides — and the agent-context risk

ggshield hmsl check does this dance, entirely on the user's machine until the underlined step:

1. Read the file.
2. SHA-256 each secret.
3. Put a hash prefix for each secret into the payload.
4. Send the payload to HMSL. ← only this leaves the machine
5. HMSL returns all known leaked hashes that share each prefix.
6. Locally, compare the returned full hashes against the user's hashes. Matches = leaked secrets.
7. Print results using the selected --naming-strategy (-n none for anything pasted back to the agent; never cleartext).

The wire protocol is safe. The threat model for this skill is different: an LLM agent has tools that can read files. If the agent reads the credential file at any point — to "check what's in it", to "verify the format", to "count lines" by accident — the plaintext enters the agent's tool output, which is part of the LLM context. At that point HMSL's local-hashing protocol is irrelevant; the secret has already been exposed to whatever downstream systems the agent's context flows through (transcripts, server logs, training pipelines if applicable, future-turn re-use).

The single job of this skill is to prepare commands for the user to run in their own terminal, then interpret sanitized output the user chooses to paste back. The agent must never run HMSL commands on the user's behalf.

Execution model — user-run only

This skill has one execution model:

• The agent prepares the exact command.
• The user runs it in their own terminal.
• The user pastes back either a human summary or JSON produced with -n none.
• The agent never has filesystem access to the credential file or HMSL intermediate files.
• The agent never runs ggshield hmsl check, ggshield hmsl fingerprint, ggshield hmsl query, ggshield hmsl decrypt, or ggshield hmsl check-secret-manager.

This is the only structurally safe model. Do not offer an agent-executed fallback, even if the user says the credential is low risk or the agent hook is installed.

The single rule that matters

Never call any tool against the credential file or HMSL intermediate files. Not Read, not Grep, not cat, head, tail, sed, awk, less, more, file, xxd, ls, wc, ggshield, or any LSP-backed tool. The agent does not need to confirm the file exists, inspect the format, count lines, or verify outputs. The user runs commands locally and decides what output to share.

If the user asks "show me what's in the file before we check it" or "just run the check for me" — refuse and explain that the credential contents must stay outside the agent context.

Why the prose rules aren't enough on their own

Prose rules can be rationalized away by the model under pressure ("the user really wants me to check the format first…"). That is why this skill has no agent-executed mode. Agent hooks and tool allowlists are useful defense in depth, but they do not make it acceptable for the agent to run HMSL against user secrets.

Other rules that close known leakage paths

• Never paste a raw secret into the conversation. If the user offers one inline ("check ghp_abc123…"), refuse and redirect: "Put it in a file and give me the path — that way the value never enters the transcript."
• Never pipe the credential through anything that surfaces it. No cat secrets.txt | ggshield ..., no echo $TOKEN | .... ggshield supports stdin, but recommended user-run commands use file-path invocation.
• --naming-strategy cleartext is forbidden. It echoes each matched secret's plaintext into stdout. Use -n none for anything pasted back to the agent.
• Use -n none for anything pasted back to the agent. Do not paste key, censored, or cleartext output into the conversation.
• Always pass --json for output the user intends to paste back.
• Do not use --full-hashes. Full-hash mode sends full SHA-256 hashes rather than prefixes; it exists for partner/trust arrangements and changes the privacy posture. Use prefix mode (default) unless the user explicitly confirms they are in partner mode.
• Do not use --insecure, --allow-self-signed, --debug, --verbose, or --log-file by default. TLS verification and quiet structured output are the safe defaults for secret-handling workflows.
• Surface quota before bulk runs. HMSL has a daily credit quota — ggshield hmsl quota first, then proceed. Prefix mode costs more quota than full-hash mode.
• ggshield hmsl is the only sanctioned path. If ggshield --version or ggshield hmsl api-status fails for the user, guide them through Onboarding (first use) below — do not improvise an alternate check (manual grep of leak databases, hand-rolled hashes, sending the secret to a different service).

When to Use

Trigger an HMSL check when:

• The user inherits credentials from a former teammate, contractor, or compromised account and wants to know which are already public
• The user suspects a specific token, key, or password may have leaked — Slack pastes, accidental commits later force-pushed away, public CI logs, etc.
• The user wants to audit a HashiCorp Vault instance against the public-leak corpus (check-secret-manager hashicorp-vault)
• The user has a list of credentials in a file (CSV, env, plain text) and wants to bulk-check them
• The user explicitly mentions "HMSL", "HasMySecretLeaked", "has this secret leaked", "is this credential compromised", "check against the public leaks", "see if this token is out there"

What ggshield hmsl covers:

• One-shot check of secrets in a file (hmsl check)
• Multi-stage privacy-preserving check: fingerprint (compute hashes locally) → query (send hash prefixes to HMSL) → decrypt (resolve which input secrets matched)
• HashiCorp Vault audit (check-secret-manager hashicorp-vault)
• Quota check (hmsl quota)
• HMSL service status (hmsl api-status)

For shared ggshield install, authentication, headless setup, CI tokens, and hook-install commands, see [references/ggshield-cli-setup.md](references/ggshield-cli-setup.md). For platform-wide topics (auth/scope recovery, instance URLs, headless setup), see [references/gitguardian-platform.md](references/gitguardian-platform.md).

When Not to Use

Do not use this skill when:

• The task is to find unknown secrets in code, files, or git history — use scan-secrets instead. This skill checks known credentials you already hold.
• You are tempted to run ggshield hmsl yourself or to read the credential file with Read, cat, Grep, or similar. HMSL operations are user-run only by design — running them agent-side pulls the plaintext into the agent context. Hand the command to the user.

Onboarding (first use)

Prerequisites

• A GitGuardian account is optional for quick checks. HMSL can run anonymously with lower quota; authenticated users get a higher workspace quota.
• ggshield 1.49.0 or later — for full feature support.

Setup

check-hmsl reuses the same ggshield install and auth login flow as scan-secrets. If the user is not sure ggshield is installed or HMSL is reachable, give them these commands to run in their own terminal:

ggshield --version
ggshield hmsl api-status

If ggshield --version fails, point them to [references/ggshield-cli-setup.md](references/ggshield-cli-setup.md). If ggshield hmsl api-status reports an auth issue, ask the user to run ggshield auth login locally.

HMSL works in two auth modes:

• Unauthenticated — no ggshield auth login needed. Lower default daily quota. Useful for quick one-off checks on a fresh machine.
• Authenticated — after ggshield auth login. Higher workspace quota than anonymous mode. Recommended for bulk inventories.

The user can confirm auth state with ggshield hmsl api-status — Authenticated: true means the call will use the user's account quota.

Install the agent hook (defense in depth)

The hook scans tool inputs and outputs in agent sessions for detected secrets and blocks before they reach the model context. It is useful defense in depth for general agent work, but it does not make agent-executed HMSL acceptable. The user can install it once, globally:

ggshield install -t claude-code -m global     # Claude Code
ggshield install -t cursor -m global          # Cursor
ggshield install -t copilot -m global         # Copilot

Whether or not the hook is installed, this skill remains user-run only.

Commands to hand to the user

The agent does not run these. The agent prints the command, the user runs it, the user pastes back the output.

# One-shot check with maximum privacy: no secret hint in the output
ggshield hmsl check /path/to/secrets.txt --json -n none

# .env-formatted input with maximum privacy
ggshield hmsl check -t env /path/to/.env --json -n none

# Quota and status
ggshield hmsl quota
ggshield hmsl api-status

For sensitive bulk audits, give the user the multi-stage flow so they can inspect the payload before stage 2 sends it:

# In their own shell, in a private temp directory outside any repo
HMSL_WORKDIR="$(mktemp -d "${TMPDIR:-/tmp}/ggshield-hmsl.XXXXXX")"
chmod 700 "$HMSL_WORKDIR"

ggshield hmsl fingerprint /absolute/path/to/secrets.txt -p "$HMSL_WORKDIR/audit" -n none
# Optional: the user can inspect "$HMSL_WORKDIR/audit-payload.txt" here.
# Do NOT inspect "$HMSL_WORKDIR/audit-mapping.txt" — keep local mapping files out of the agent context.

ggshield hmsl query "$HMSL_WORKDIR/audit-payload.txt" > "$HMSL_WORKDIR/results.dump"

ggshield hmsl decrypt "$HMSL_WORKDIR/results.dump" --mapping "$HMSL_WORKDIR/audit-mapping.txt" --json

rm -rf "$HMSL_WORKDIR"

The user pastes back only the final decrypt --json output (or just the human summary). Stage outputs stay on their machine.

Secret-manager inventory

Secret-manager inventories are high-risk by default. The agent must not run this command. Hand it to the user:

# Vault URL from VAULT_URL or --url; token from VAULT_TOKEN unless --use-cli-token
ggshield hmsl check-secret-manager hashicorp-vault \
  --url https://vault.example.com \
  --recursive \
  --json \
  secret/

ggshield hmsl check-secret-manager --help lists currently-supported managers. The HashiCorp Vault command supports KV v1/v2.

Operational commands

ggshield hmsl quota         # remaining credits today
ggshield hmsl api-status    # confirm HMSL is reachable + whether the CLI is authenticated

Key flags (applicable to check and fingerprint):

| Flag | Effect | |---|---| | --json | Structured output — use for anything the user intends to paste back | | -t file\|env | Input format. file = one secret per line (default). env = KEY=VALUE lines | | -n key\|censored\|none\|cleartext | Hint format for matched secrets in the output. Use none for anything pasted back to the agent. Do not paste key, censored, or cleartext output into the conversation | | -f, --full-hashes | Send full hashes instead of prefixes. Do not use in normal agent contexts; partner/trust mode only | | -p, --prefix | (fingerprint only) Prefix for generated -payload.txt / -mapping.txt files | | -m, --mapping | (decrypt only) Path to the mapping file from fingerprint |

Exit codes: 0 = no matches found, 1 = at least one secret matched (leaked publicly), non-zero = error (auth, quota, HMSL unreachable).

Best Practices

• Never run HMSL commands on behalf of the user. The agent prepares commands only.
• Default to -n none for output pasted back to the agent. Do not ask the user to paste output generated with -n key, -n censored, or -n cleartext.
• Ask the user to check quota before bulk runs. Prefix mode currently consumes multiple credits per checked secret, so ggshield hmsl quota first.
• For a small handful of secrets, use check. For sensitive bulk audits, use the fingerprint / query / decrypt split. The split lets the user inspect what's being sent and decouples the local hashing step from the network call.
• Treat a match as confirmation, not coincidence. HMSL's corpus is built from indexed public sources — a match means GitGuardian saw your exact secret in a public artifact. The credential is public and must be considered burned: rotate it at the issuing service and update every system that consumes it. Takedown of the public source does not substitute for rotation.
• HMSL is read-only. A check does not "report" or "remove" the secret from anywhere — it only tells the user it's already public. Removal requires takedown action on the underlying source (e.g., a public GitHub repo).
• The hash field in HMSL output is a one-way SHA-256 — safe to report back to the user, but don't publish it in issues, PR comments, or logs unless the user asks. The url field points to a public source (e.g., a leaked GitHub commit) — safe and useful; this is the actionable information.

Troubleshooting

ggshield: command not found — see the scan-secrets skill's Onboarding section.

401 Unauthorized on hmsl commands — the cached HMSL token is stale. Delete it and re-authenticate:

rm ~/.cache/ggshield/hmsl_token   # path on macOS/Linux
ggshield auth login                # if `Authenticated: false` in api-status
ggshield hmsl api-status           # confirm

429 Too Many Requests / "quota exceeded" — daily quota is gone. Run ggshield hmsl quota to see the reset time. Either wait for the reset or switch to an authenticated account with a higher quota.

HMSL api-status shows Authenticated: false — the CLI is hitting HMSL anonymously. Run ggshield auth login to get the authenticated quota. Anonymous mode works but caps out quickly.

No matches found on a secret you know was leaked — HMSL covers the public sources GitGuardian has indexed for HMSL, currently public GitHub repositories, commits, gists, and issues. If the leak was in a private repo, an unindexed paste site, or a non-public artifact, HMSL won't see it. For the user's private GitGuardian workspace incidents, see the GitGuardian dashboard or the incidents to

…

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: GitGuardian
• Source: GitGuardian/agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.