Event Filtering

Route events to endpoints based on payload content using filter expressions.

Filter syntax

Filters use JSONPath-style expressions evaluated against the event payload:

{
  "filter": [
    { "field": "$.data.amount", "operator": "gte", "value": 1000 },
    { "field": "$.data.currency", "operator": "eq", "value": "USD" }
  ]
}

All conditions must match (AND logic by default). An endpoint whose filter doesn’t match is skipped for that event. If that leaves no endpoint to deliver to (none subscribes to the event type, or every subscriber’s filter excludes the payload), POST /api/v1/events returns 400 NO_MATCHING_ENDPOINTS and no event is stored.

Operators

Operator	Description	Example
`eq`	Equal	`"$.status" eq "active"`
`ne`	Not equal	`"$.type" ne "test"`
`gt`	Greater than	`"$.amount" gt 100`
`gte`	Greater or equal	`"$.amount" gte 1000`
`lt`	Less than	`"$.priority" lt 5`
`lte`	Less or equal	`"$.retry_count" lte 3`
`contains`	String contains	`"$.email" contains "@company.com"`
`startsWith`	String starts with	`"$.path" startsWith "/api/"`
`endsWith`	String ends with	`"$.file" endsWith ".pdf"`
`exists`	Field exists	`"$.metadata.tags" exists true`
`regex`	Regex match	`"$.code" regex "^[A-Z]{3}$"`

Logical combinators

For complex filtering, use and, or, and not:

{
  "filter": {
    "or": [
      { "field": "$.data.amount", "operator": "gte", "value": 10000 },
      {
        "and": [
          { "field": "$.data.currency", "operator": "eq", "value": "USD" },
          { "field": "$.data.priority", "operator": "eq", "value": "high" }
        ]
      }
    ]
  }
}

Nesting is supported up to 10 levels deep.

Example: Route high-value orders

curl -X POST https://app.mittr.io/api/v1/endpoints \
  -H "X-API-Key: mtr_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "url": "https://billing.example.com/webhooks",
    "eventTypes": ["order.created"],
    "filter": [
      { "field": "$.data.amount", "operator": "gte", "value": 10000 }
    ]
  }'

Only order.created events with data.amount >= 10000 are delivered to this endpoint.

Combined with fan-out

Filters work alongside event type subscriptions:

An event is sent with eventType: "order.created"
Mittr finds all endpoints subscribed to order.created (or order.*)
Each endpoint’s filter is evaluated against the payload
Only matching endpoints receive the delivery

This allows fine-grained routing without duplicating events.