pyveil 0.1.1

Redact secrets before your AI agent sees them

pyveil

Redact secrets before your AI agent sees them.

pyveil is agent-native redaction middleware for prompts, tool calls, MCP resources, logs, traces, and memory. Put it before sensitive context reaches a model, tool, memory store, trace exporter, or log sink.

user data / tool data / resource data
        -> pyveil
        -> agent prompt / tool call / MCP resource / memory / trace / log

pyveil is intentionally small: standard-library core, deterministic HMAC placeholders, channel-aware policy, and high-precision detectors for v0.1.

Install

pip install pyveil

Python 3.8 through 3.14 are tested.

30 Second Quickstart

from pyveil import Veil

veil = Veil.high(secret=b"tenant-or-run-secret", scope="tenant/session")

result = veil.redact_text(
    "Email [e-mail] and call 010-1234-5678",
    channel="prompt.input",
)

print(result.text)
# Email [EMAIL:...] and call [PHONE:...]

For one-off scripts:

from pyveil import redact_text

safe = redact_text(
    "email [e-mail]",
    secret=b"tenant-or-run-secret",
    scope="tenant/session",
)
print(safe.text)

Usage Guides

Short no-audio walkthroughs are attached to the v0.1.1 GitHub release:

• English usage guide
• Korean usage guide

Why Middleware

Prompt-only redaction asks the model to handle sensitive data after the model has already seen it. pyveil redacts before context crosses an agent boundary.

Classic PII masking libraries usually treat redaction as "text in, text out." Agents leak through more surfaces:

Channel	Typical use
prompt.input	User or retrieved context before model input
prompt.output	Model output before display or chaining
tool.call.arguments	Arguments before a model-controlled tool runs
tool.call.result	Tool results before returning to the model
mcp.resource.content	MCP resource content before agent use
memory.write	Memory text before embedding or persistence
trace.span.attributes	Observability attributes before export
log.record	Application logs before handlers or sinks

Channels are first-class so policy can decide whether a finding should be redacted, passed, or blocked.

Text Redaction

from pyveil import Channel, Veil

veil = Veil.high(
    secret=b"tenant-secret",
    scope="tenant_123/session_456",
    max_input_chars=1_000_000,
)

safe = veil.redact_text(
    "Authorization: Bearer synthetic-token-value",
    channel=Channel.PROMPT_INPUT,
)

print(safe.text)
print(safe.findings[0].type)

Finding objects do not contain raw sensitive values by default. They include metadata such as type, detector, rule_id, path, placeholder, and fingerprint.

Structured Redaction

Use redact_data for dictionaries, lists, JSON strings, tool arguments, MCP-like payloads, trace attributes, and memory records.

from pyveil import Veil

payload = {
    "user": "[e-mail]",
    "headers": {"Authorization": "Bearer synthetic-token-value"},
    "args": {"phone": "[phone]"},
    "debug": True,
}

veil = Veil.high(secret=b"tenant-secret", scope="tenant/session")
safe = veil.redact_data(payload, channel="tool.call.result")

print(safe.data)

Structured payloads keep their shape. Non-string scalar values under sensitive key names, such as {"api_key": 12345} or {"password": True}, preserve their original type instead of being replaced with strings.

HIGH vs LOW

Use HIGH by default for agents and external boundaries.

Level	Intended use	Example
HIGH	Agent, model, tool, MCP, memory, trace, and log boundaries	[e-mail] -> [EMAIL:a13f7c91b0d2]
LOW	Human-facing diagnostics or legacy-style previews	[e-mail] -> al***@e******.com

Credential-like values remain aggressively hidden. There is no reversible vault or unmasking API in v0.1.

Policy

The default policy redacts supported findings and blocks credential-like material in tool.call.arguments.

from pyveil import Action, Channel, Entity, Policy, Veil

policy = Policy.default_high().override(
    Channel.PROMPT_INPUT,
    Entity.EMAIL,
    Action.PASS,
)

veil = Veil.high(secret=b"tenant-secret", policy=policy)

When both policy and level are supplied, the explicit policy decides channel levels and actions. Build one Veil per tenant, session, or run and reuse it in tight loops.

CLI

pyveil init
export PYVEIL_SECRET="tenant-or-run-secret"
export PYVEIL_SCOPE="tenant/session"

pyveil redact prompt.txt --channel prompt.input --level high
pyveil redact request.json --channel tool.call.result --format json
pyveil scan prompt.txt --format json
pyveil test-config pyveil.yaml

JSON-shaped input is treated as structured data. Use --format json for pyveil redact when the input is JSON.

Detectors

v0.1 focuses on high-precision, low-dependency detection:

• Email addresses
• Korean and international-ish phone numbers
• Credit card numbers with Luhn validation
• JWTs
• Bearer and Basic authorization headers
• Private key blocks
• Common API key and provider token prefixes
• URL query secrets such as access_token=
• Key-value secrets in text and structured payloads

Broad name and address detection is intentionally out of scope for core v0.1 unless supplied as known values or custom rules in a future release.

Safety Model

pyveil aims to reduce sensitive-context exposure at agent boundaries.

• No raw sensitive value is stored in Finding by default.
• Stable placeholders use HMAC-SHA256 with caller-provided secrets.
• scope separates placeholders across tenants, sessions, or runs.
• max_input_chars limits input size before detection.
• Core v0.1 has no network calls and no required third-party runtime dependencies.

Use it with access control, logging discipline, secret scanning, provider-side controls, and normal application security review.

Non-goals

pyveil is not:

• A Presidio clone
• An enterprise DLP system
• A compliance guarantee
• A secret-scanning replacement
• A prompt-injection firewall
• A reversible token vault

Agent Adoption

This repository includes files meant for coding agents and LLM readers:

• AGENTS.md for agent instructions
• llms.txt for LLM-friendly navigation
• docs/threat-model.md
• docs/known-limitations.md
• docs/detector-provenance.md
• docs/release-checklist.md
• docs/integrations/mcp.md
• docs/integrations/logging.md
• docs/integrations/tracing.md

Examples:

• examples/basic_usage.py
• examples/redact_json.py
• examples/log_filter.py
• examples/mcp_tool_result.py
• examples/memory_write.py

Development

uv run --extra dev ruff check .
uv run --extra dev mypy pyveil tests
uv run --extra test pytest

Full local release check:

for v in 3.8 3.9 3.10 3.11 3.12 3.13 3.14; do
  UV_PROJECT_ENVIRONMENT="/tmp/pyveil-venv-$v" uv run --python "$v" --extra test pytest -q --disable-warnings --no-cov
done

uv run --extra dev python -m build
uv run --extra dev python -m twine check dist/*