Guardrails Configuration - Hoop.dev - Automated Access and Data Protection

Guardrails use pattern matching to evaluate queries and block dangerous operations before they execute. This page covers configuration options and rule syntax.

For an introduction to what Guardrails do and common use cases, see Guardrails Overview.

Prerequisites

Guardrails are evaluated by the Microsoft Presidio Analyzer — patterns and word lists are sent to Presidio as ad-hoc recognizers, and matching happens inside Presidio.

Presidio is required. There is no fallback engine. If a resource role has a guardrail assigned and Presidio is not deployed or the gateway cannot reach it, queries on that resource role will fail.

Before configuring guardrails, deploy Presidio and point the gateway at it:

Deploy Presidio

Helm chart, sizing, and autoscaling for the Analyzer, Anonymizer, and Envoy Proxy.

Microsoft Presidio Integration

Required gateway environment variables and integration overview.

Creating a Guardrail

Navigate to Guardrails

In the Web App, open the Discover section in the sidebar and select Guardrails

Create New Guardrail

Click Create New Guardrail in the top-right corner

Set Basic Information

Name: A short identifier (e.g., block-ddl, read-only-mode)
Description: Explain what this guardrail protects against

Add Rules

Configure Input Rules and/or Output Rules (see below)

Assign Resource Roles

Select which resource roles this guardrail applies to

Save

Click Save to activate the guardrail

Rule Configuration

Input Rules

Input rules evaluate queries before they execute. Use these to block dangerous commands.

Field	Description	Example
Pattern	Regex pattern to match	`(?i)DROP\s+TABLE`
Action	What to do when pattern matches	Block, Warn, Require Approval
Message	Error message shown to user	`DDL commands are blocked`

Output Rules

Output rules evaluate query results after execution. Use these to filter or redact output.

Field	Description	Example
Pattern	Regex pattern to match in output	`\b\d{3}-\d{2}-\d{4}\b` (SSN)
Action	What to do when pattern matches	Redact, Block, Warn
Replacement	Text to replace matches with	`[REDACTED]`

For data masking that automatically detects PII, see Live Data Masking instead.

Pattern Syntax

Guardrail patterns are compiled by Microsoft Presidio, which uses Python’s re module. Write patterns using Python regex syntax — not JavaScript/ECMAScript and not Go’s RE2.

Basic Syntax

Syntax	Meaning	Example
`(?i)`	Case-insensitive	`(?i)drop` matches `DROP`, `Drop`, `drop`
`\s+`	One or more whitespace	`DROP\s+TABLE` matches `DROP TABLE`
`\s*`	Zero or more whitespace	`DROP\s*TABLE` matches `DROPTABLE` too
`\b`	Word boundary	`\bDROP\b` won’t match `BACKDROP`
`^`	Start of string	`^SELECT` only matches SELECT at start
`$`	End of string	`;\s*$` matches trailing semicolon
`.*`	Any characters	`SELECT.*FROM` matches anything between
`(?!...)`	Negative lookahead	`(?!.*WHERE)` means “not followed by WHERE”

Common Patterns

Block UPDATE without WHERE:

(?i)^\s*UPDATE\s+\w+\s+SET\s+(?!.*WHERE)

Block DELETE without WHERE:

(?i)^\s*DELETE\s+FROM\s+\w+(?!.*WHERE)

Block all DDL:

(?i)^\s*(DROP|CREATE|ALTER|TRUNCATE)\s+(TABLE|DATABASE|INDEX|SCHEMA|VIEW)

Block SELECT * on specific tables:

(?i)SELECT\s+\*\s+FROM\s+(users|orders|transactions)

Require LIMIT clause:

(?i)SELECT\s+(?!.*\bLIMIT\b).*FROM

Enforce read-only access (create separate rules for each):

Pattern	Blocks
`(?i)^\s*INSERT\s+INTO`	INSERT statements
`(?i)^\s*UPDATE\s+`	UPDATE statements
`(?i)^\s*DELETE\s+FROM`	DELETE statements
`(?i)^\s*(CREATE	DROP	ALTER)\s+`	DDL commands

Apply read-only patterns only to resource roles used by read-only groups, not to admin resource roles.

Prevent credential access — block queries that might expose passwords or secrets:

(?i)SELECT\s+.*\bFROM\s+\w*users\w*.*\b(password|secret|token|api_key)\b

Block specific table access — restrict sensitive tables like salaries or api_keys:

(?i)\b(FROM|JOIN|INTO|UPDATE)\s+(salaries|api_keys|credentials|secrets)\b

Testing Patterns

Before deploying a pattern, test it at regex101.com:

Select Flavor: Python
Paste your pattern in the Regular Expression field
Enter test queries in the Test String field
Verify matches highlight correctly

Inline flags ((?i), (?m), (?s)), lookaheads ((?!...)), lookbehinds ((?<=...)), and word boundaries (\b) are all supported by Python’s re. Avoid JavaScript-only constructs — for example, Python’s named groups use (?P<name>...), not (?<name>...).

Actions

Block

Prevents the query from executing and returns an error. Use when: The operation should never be allowed (e.g., DROP TABLE in production) User sees:

Error: Guardrail violation
Rule: block-ddl
Message: DDL commands are blocked in production

Warn

Allows the query but shows a warning message. Use when: You want to educate users without blocking work (e.g., missing LIMIT) User sees:

Warning: Consider adding a LIMIT clause to prevent large result sets
Query executed successfully.

Require Approval

Blocks the query until an approver approves it. Use when: Some queries need human review before execution (e.g., bulk updates) User sees:

This query requires approval.
Waiting for approval at https://use.hoop.dev/access-requests/abc123...

Require Approval uses the same workflow as Action Access Requests.

Resource Role Assignment

Each guardrail can be assigned to multiple resource roles. You can also have multiple guardrails on a single resource role.

Assignment Options

Option	Description
Specific resource roles	Select individual resource roles from the list
All resource roles	Apply to every resource role in your organization
Resource role tags	Apply to resource roles matching specific tags

Evaluation Order

When multiple guardrails apply to a resource role, they are evaluated in order of priority:

Priority 1 (highest) evaluated first
First matching rule determines the action
If no rules match, query is allowed

To set priority:

Open Discover > Guardrails in the sidebar
Drag guardrails to reorder them
Higher position = higher priority

Environment Variables

Guardrails run inside Microsoft Presidio, so they share the same gateway environment variables as Live Data Masking. Configure these on the gateway — guardrails will not evaluate without them:

Variable	Description	Example
`DLP_PROVIDER`	Must be set to enable Presidio-backed guardrails	`mspresidio`
`MSPRESIDIO_ANALYZER_URL`	URL of the Presidio Analyzer service	`http://presidio-envoy-lb:3010`
`MSPRESIDIO_ANONYMIZER_URL`	URL of the Presidio Anonymizer service	`http://presidio-envoy-lb:3010`
`DLP_MODE`	`best-effort` or `strict` (shared with Live Data Masking)	`best-effort`

For deployment details (workers, autoscaling, models), see Microsoft Presidio Deployment.

Testing Guardrails Safely

Always test guardrails before applying them to production resource roles.

Testing Process

Create a Test Resource Role

Create a separate resource role to the same database (e.g., prod-db-test)

Apply the Guardrail

Assign the guardrail only to the test resource role

Run Test Queries

Test both queries that should be blocked and queries that should pass

Verify Results

Confirm the guardrail blocks what it should and allows what it should

Apply to Production

Once verified, add production resource roles to the guardrail

Worked Example

Try running a query that should be blocked:

hoop exec prod-db -i "UPDATE users SET status = 'inactive'"

Expected output:

Error: Guardrail violation
Rule: block-unsafe-updates
Message: Blocked: UPDATE/DELETE requires a WHERE clause

Now run a query that should pass:

hoop exec prod-db -i "UPDATE users SET status = 'inactive' WHERE id = 123"

This query executes normally because it includes a WHERE clause. For each guardrail, test:

Should block: A query that matches the pattern exactly
Should allow: A similar query that doesn’t match
Edge cases: Queries with different casing, extra whitespace, or variations

Monitoring Guardrails

Viewing Blocked Queries

Go to Sessions in the sidebar
Filter by Status: Blocked
Click a session to see details

Each blocked session shows:

The query that was blocked
Which guardrail and rule triggered
The error message
User and timestamp

Audit Log

All guardrail evaluations are logged:

Blocked queries - Logged with full query text
Warnings - Logged with warning message
Approval requests - Logged with request status

Access audit logs in Sessions or export via the API.

Emergency Bypass

If a legitimate query is blocked and needs to run immediately:

Option 1: Temporarily Disable the Guardrail

Open Discover > Guardrails in the sidebar
Find the blocking guardrail
Toggle it to Disabled
Run your query
Re-enable the guardrail immediately after

Document any emergency bypass in your incident log. Re-enable the guardrail as soon as possible.

Option 2: Refine the Pattern

If the guardrail is catching legitimate queries, update the pattern:

Open Discover > Guardrails and select the guardrail
Edit the rule that’s causing issues
Refine the regex to be more specific
Save and test

Option 3: Add an Exception

For specific users or groups that need to bypass certain rules:

Create a new resource role without the guardrail
Restrict access to that resource role to specific groups
Use this “elevated” resource role for exceptional cases

Best Practices

Start with Warn

Use Warn mode first to understand impact before blocking

Test in Dev First

Apply guardrails to test resource roles before production

Be Specific

Use precise patterns to avoid false positives

Document Rules

Write clear descriptions explaining why each rule exists

Pattern Guidelines

Always use (?i) for case-insensitive matching
Use \b for word boundaries to avoid partial matches
Use ^\s* to allow leading whitespace
Test edge cases like multi-line queries and comments
Keep patterns simple - complex regex is hard to maintain

Troubleshooting

Pattern Not Matching

Check:

Test the pattern at regex101.com with the exact query
Verify case sensitivity (add (?i) if needed)
Check for leading/trailing whitespace in the query

Common pattern mistakes:

Problem	Bad Pattern	Fixed Pattern
Missing case-insensitive	`DROP TABLE`	`(?i)DROP TABLE`
Missing word boundaries	`DELETE`	`\bDELETE\b`
Anchoring too strict	`^DROP`	`^\s*DROP` (allows leading whitespace)

Too Many False Positives

Fix:

Make the pattern more specific
Add word boundaries (\b)
Use negative lookahead for exceptions

Example: Pattern DROP blocks DROP_SHIPPED_ITEMS table name Fix: (?i)^\s*DROP\s+(TABLE|DATABASE) only matches DDL commands

Performance Issues

If queries are slow:

Reduce the number of rules per resource role
Simplify complex regex patterns
Avoid patterns with excessive backtracking (e.g., .*.*.*)

Guardrails Overview

Learn what guardrails do and see common recipes

Live Data Masking

Configure automatic PII detection and masking

Action Access Requests

Configure the “Require Approval” action

Access Control

Control who can access which resource roles

​Prerequisites

Deploy Presidio

Microsoft Presidio Integration

​Creating a Guardrail

​Rule Configuration

​Input Rules

​Output Rules

​Pattern Syntax

​Basic Syntax

​Common Patterns

​Testing Patterns

​Actions

​Block

​Warn

​Require Approval

​Resource Role Assignment

​Assignment Options

​Evaluation Order

​Environment Variables

​Testing Guardrails Safely

​Testing Process

​Worked Example

​Monitoring Guardrails

​Viewing Blocked Queries

​Audit Log

​Emergency Bypass

​Option 1: Temporarily Disable the Guardrail

​Option 2: Refine the Pattern

​Option 3: Add an Exception

​Best Practices

Start with Warn

Test in Dev First

Be Specific

Document Rules

​Pattern Guidelines

​Troubleshooting

​Pattern Not Matching

​Too Many False Positives

​Performance Issues

​Related

Guardrails Overview

Live Data Masking

Action Access Requests

Access Control

Prerequisites

Creating a Guardrail

Rule Configuration

Input Rules

Output Rules

Pattern Syntax

Basic Syntax

Common Patterns

Testing Patterns

Actions

Block

Warn

Require Approval

Resource Role Assignment

Assignment Options

Evaluation Order

Environment Variables

Testing Guardrails Safely

Testing Process

Worked Example

Monitoring Guardrails

Viewing Blocked Queries

Audit Log

Emergency Bypass

Option 1: Temporarily Disable the Guardrail

Option 2: Refine the Pattern

Option 3: Add an Exception

Best Practices

Pattern Guidelines

Troubleshooting

Pattern Not Matching

Too Many False Positives

Performance Issues

Related