Today we're launching Mutation Rules v2, our biggest platform update since launch. This release makes Stage dramatically more powerful while also being easier to use.

What's New

JSON Path Expressions

You can now use JSON Path to surgically target specific fields in API responses:

json

{
  "match": { "path": "/api/products/*" },
  "action": {
    "type": "patch",
    "operations": [
      { "op": "replace", "path": "$.price.amount", "value": 0.01 },
      { "op": "add", "path": "$.flags", "value": ["test_mode"] }
    ]
  }
}

Conditional Logic

Rules can now include conditions that evaluate request or response data:

json

{
  "match": {
    "path": "/api/users/*",
    "conditions": [
      { "field": "$.role", "equals": "admin" }
    ]
  },
  "action": { "type": "latency", "ms": 5000 }
}

This is perfect for testing how your app handles slow responses for specific user types.

Visual Rule Builder

For teams who prefer a GUI, we've built a visual rule builder that generates JSON configuration automatically. No more hand-editing config files!

Response Templates

Create reusable response templates for common scenarios:

Payment declined: Standard response for testing declined transactions
Rate limited: 429 response with retry headers
Service unavailable: 503 with maintenance message

Migration Guide

Existing rules continue to work without changes. If you want to take advantage of new features, check out our migration guide.

What's Next

We're already working on:

Request mutation: Modify outgoing requests, not just responses
Webhooks: Trigger actions when rules match
Analytics: See which rules are being triggered and how often

Try Mutation Rules v2 today or read the docs.

Introducing Mutation Rules v2: More Power, Less Complexity