drape

Hide secrets from LLMs when reading config files.

drape is a defense-in-depth tool for Claude Code and other AI agents. It masks credentials in .env, SOPS-encrypted .env.sops, and structured (YAML / JSON / TOML) config files so they never appear in LLM conversations, prompt-cache snapshots, or provider logs.

Your real .env is never modified. Plaintext is never written to disk. The masking happens in-process on your machine before the agent sees anything.

Quick demo

$ cat .env
DATABASE_URL=postgres://user:hunter2@localhost/db
AWS_ACCESS_KEY_ID=AKIA<example-redacted-for-readme>
GITHUB_TOKEN=ghp_<example-redacted-for-readme>
APP_PASSWORD=correct-horse-battery-staple
JWT=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.<example>
RANDOM_HEX=a8f3c9e7b2d1f4a6c8e0b9d7f2a1c4e6

$ drape .env
DATABASE_URL=<basic-auth>
AWS_ACCESS_KEY_ID=<aws-access-key>
GITHUB_TOKEN=<github-token>
APP_PASSWORD=cor...
JWT=<jwt>
RANDOM_HEX=a8f...

Recognized credentials are reduced to a type label. Unknown values reveal at most three characters (capped to 25 % of the value's length).

How it masks

Three strategies, applied in order — the most-protective hit wins:

1. Pattern recognition — known credential shapes are replaced with a type label, e.g. <aws-access-key>, <github-token>. The LLM learns what kind of credential is at this key, but zero characters of it. Powered by detect-secrets; ~21 detectors enabled by default:

   Detector	Label
   AWS access keys	<aws-access-key>
   Azure storage keys	<azure-storage-key>
   GitHub / GitLab tokens	<github-token> / <gitlab-token>
   Slack tokens	<slack-token>
   Stripe keys	<stripe-key>
   Square OAuth tokens	<square-oauth-token>
   Twilio keys	<twilio-key>
   Discord bot tokens	<discord-bot-token>
   Mailchimp / Mailgun / SendGrid	<mailchimp-key> / <mailgun-key> / <sendgrid-key>
   npm tokens	<npm-token>
   JWTs	<jwt>
   Private keys (RSA / EC / OpenSSH / PGP)	<private-key>
   Basic-auth URIs	<basic-auth>
   Artifactory tokens	<artifactory-token>
   IBM Cloud (IAM, COS, Cloudant)	<ibm-cloud-iam-key> etc.
   OpenAI / Anthropic keys	<openai-key> / <anthropic-key>

2. Entropy-aware reveal — values whose Shannon entropy is below the threshold (default 3.0 bits/char) get the label <low-entropy-secret>. Catches passwords like hunter2 or correct horse battery staple whose 3-char prefix would otherwise leak meaningful information.

3. Length-bounded prefix — for high-entropy values that didn't match any pattern, reveal the first N characters (default 3), capped at 25 % of the value length, with a minimum of 1:

   POSTGRES_PASSWORD=wFw...
   

Surrounding quotes are stripped before any of this, so KEY="abcd" reveals chars from abcd, not "abcd".

Installation

drape is distributed as a uv tool — install once, run from anywhere:

uv tool install drape                 # core (.env + .env.sops)
uv tool install 'drape[yaml]'         # + YAML support
uv tool install 'drape[toml]'         # + TOML on Python <3.11
uv tool install 'drape[all]'          # everything

To run without installing:

uvx drape .env
uvx --from 'drape[all]' drape --format yaml config/secrets.yaml

Or from source:

git clone https://github.com/pike00/drape.git
cd drape
uv tool install .

Requires Python 3.9+ (uv manages this automatically). SOPS support requires the sops binary on $PATH.

Usage

Command line

drape .env                                # plain .env
drape config/.env.production              # variants ok
drape infra/secrets.env.sops              # SOPS-encrypted (decrypts in-process)
drape --format yaml config/secrets.yaml   # YAML key-pattern masking
drape --format json config/secrets.json   # JSON
drape --format toml pyproject.toml        # TOML
drape --prefix-chars 5 .env               # reveal up to 5 chars (still 25%-capped)
drape --no-patterns .env                  # disable type-label detection
drape --entropy-threshold 0 .env          # restore "reveal everything" behavior

Format auto-detects from filename for .env, .env.sops, .yaml, .yml, .json, .toml. Override with --format when needed.

Claude Code integration (primary use case)

drape ships a PreToolUse hook that intercepts file reads before they reach the model. Install once per project:

uv tool install drape
bash scripts/install-claude-hook.sh --project-dir /path/to/project

The installer adds the right entries to .claude/settings.json automatically. After restarting Claude:

Claude asks:  What's in .env?
Claude sees:  POSTGRES_PASSWORD=wFw...
              AWS_KEY=<aws-access-key>
              GITHUB_PAT=<github-token>

The hook covers three tools, not just Read:

• Read on a secrets file — replaced with the masked rendering
• Grep on a secrets file — re-greps against the masked rendering, so matches on a key still surface but the value stays hidden
• Bash commands that try to read a secrets file directly (cat .env, head .env.sops, grep PASSWORD .env, rg KEY .env.sops, awk -F= '...' .env, …) — the hook returns a denial that redirects the agent to drape

For step-by-step setup: docs/SETUP.md. For publishing notes: docs/PUBLISHING.md.

Python API

from pathlib import Path
from drape import parse_env_file, mask_value, classify_secret

# Mask a whole file
for line in parse_env_file(Path(".env"), prefix_chars=4):
    print(line)

# Mask a single value
mask_value("AKIAIOSFODNN7EXAMPLE")          # -> "<aws-access-key>"
mask_value("hunter2")                        # -> "<low-entropy-secret>"
mask_value("R8aFq9wKjL2pXmZbT3vH")          # -> "R8a..."

# Just classify (no masking)
classify_secret("ghp_1234567890abcdef...")  # -> "<github-token>"
classify_secret("just a string")             # -> None

Security threat model

What drape protects against

• Secrets appearing in LLM conversation transcripts
• Provider logging / prompt-cache snapshots of full secrets
• Accidental copy-paste of credentials into chat
• Third-party access to session history (e.g., shared/exported transcripts)

What drape does not protect against

• Compromised local machine — if an attacker can read your .env directly, drape doesn't help
• Compromised LLM account — anyone with your account can request unmasked files
• File permissions — drape reads whatever your shell can read
• Multiline secrets in .env — only single-line KEY=VALUE parses correctly (use a structured format for multiline values)

Threat scenario prevented

• Attacker gains read-only access to Claude conversation transcripts
• Masked content shows: AWS_KEY=<aws-access-key> (zero chars revealed) or RANDOM=a8f... (3 chars, ~10^15 brute-force space for a 22-char value)
• Even with full pattern knowledge, the type label is not enough to authenticate

See docs/architecture.md for the detailed threat model and design rationale, and docs/ROADMAP.md for planned features.

Configuration

All knobs are settable via CLI flags and/or environment variables. The hook reads only the env vars (CLI flags don't apply when Claude invokes drape).

Setting	CLI flag	Env var	Default
Max prefix chars revealed	--prefix-chars N	DRAPE_PREFIX_CHARS	3
Entropy threshold (bits/char)	--entropy-threshold F	DRAPE_ENTROPY_THRESHOLD	3.0
Disable pattern type-labels	--no-patterns	(n/a)	enabled
Format override	--format <fmt>	(n/a)	auto
Extra hook glob patterns	(n/a)	DRAPE_HOOK_PATTERNS	unset
Audit log path (JSONL)	(n/a)	DRAPE_AUDIT_LOG	unset
Log level	(n/a)	DRAPE_LOG_LEVEL	INFO

Cap behavior

The 25 % cap is unconditional: asking for 8 chars on a 12-char secret reveals only 3 (12 // 4 = 3); asking for 5 on a 4-char secret reveals only 1. Order of precedence:

empty                  → ""
matches a pattern      → <credential-type>
entropy < threshold    → <low-entropy-secret>
otherwise              → first min(prefix, len // 4, ≥1) chars + "..."

Audit log

Set DRAPE_AUDIT_LOG=/path/to/audit.jsonl to record every masking operation. Each line is a JSON object with ts, event, file, format, key_count, and prefix_chars. Values are never logged — only the fact that a file was masked, what shape it was, and how many keys it contained.

$ DRAPE_AUDIT_LOG=~/.drape-audit.jsonl drape .env > /dev/null
$ tail -1 ~/.drape-audit.jsonl
{"ts":"2026-05-06T19:30:00+00:00","event":"cli_mask","file":".env","format":"env","key_count":12,"prefix_chars":3}

The audit writer never raises — if the log path is unwritable, masking still succeeds.

File patterns

The hook intercepts these file shapes by default:

• .env, *.env (e.g., production.env, app.env)
• .env.sops, *.env.sops — decrypted via the sops binary in-process, then masked

It explicitly skips:

• .env.example, .env.sample, .env.template
• .env.json, .env.yaml, .env.yml, .env.toml (use --format on the CLI for these)

Add extra glob patterns via DRAPE_HOOK_PATTERNS=*.secrets.yaml,credentials.json.

Structured-format key matching

For YAML / JSON / TOML, drape walks the document and masks any leaf value whose key contains a secret-looking substring (case-insensitive):

password    passwd        secret       token       api_key      apikey
auth        credential    private_key  access_key  client_secret
session     cookie        salt         signature

Output is always rendered as flat dotted.path=masked lines so the LLM sees one consistent shape across all formats.

Development

git clone https://github.com/pike00/drape.git
cd drape
uv sync --group dev          # install dev deps
uv run pytest                # 64 tests, ~1s
uv run pytest --cov          # with coverage report (target: ≥84%)
uv run ruff check src tests
uv run black --check src tests

The test suite covers: masker logic, all detect-secrets pattern integrations, entropy thresholds, structured-format walkers, SOPS dispatch (with the sops binary stubbed), the Claude hook (Read / Grep / Bash variants), audit log emission, and CLI argument parsing.

Limitations

• Single-line .env values — multiline values aren't parsed; use YAML / JSON / TOML for those
• Structured formats use key-name heuristics — a key not matching the secret-keyword list is rendered in the clear, even if its value looks like a credential. (The CLI's --format env mode still runs full pattern + entropy detection on every value.)
• No on-demand unmasking — once masked, the model can't ask for the real value (planned for a future release with re-authentication)

Contributing

See CONTRIBUTING.md for guidelines.

License

MIT — see LICENSE.

Contact

For security issues, email will@khanpikehome.com instead of opening a public issue.

Related work

• direnv — load .env files in your shell
• python-dotenv — load .env in Python apps
• SOPS — encrypt .env and YAML / JSON files at rest
• detect-secrets — the credential-detection engine drape uses for pattern matching
• git-secrets — pre-commit-hook approach to keeping secrets out of repos