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Starts With

Checks if a string value starts with a specified prefix.

Overview​

The starts_with condition evaluates whether a field's string value begins with a specified prefix. This is useful for matching URL paths, ID prefixes, namespace patterns, and other cases where the beginning of a string is significant.

Use Cases​

  • URL Path Routing: Route based on URL path prefixes
  • ID Namespace Matching: Match IDs with specific prefixes
  • Environment Detection: Identify environments by hostname prefixes
  • Log Source Routing: Route logs based on source prefixes

Configuration​

SettingTypeRequiredDescription
keystringYesThe field path to check. Supports dot notation for nested fields. Use * to check all keys.
valuestringYesThe prefix to check for.
case_insensitivebooleanNoIf true, performs case-insensitive comparison.
notbooleanNoIf true, inverts the condition (matches if value does NOT start with prefix).

Examples​

URL Path Routing​

Route API requests:

{
  "type_id": "starts_with",
  "config": {
    "key": "path",
    "value": "/api/v2/"
  }
}

Matches:

{"path": "/api/v2/users"}
{"path": "/api/v2/orders/123"}
{"path": "/api/v2/"}

Does not match:

{"path": "/api/v1/users"}
{"path": "/web/dashboard"}
{"path": "api/v2/users"}

ID Prefix Matching​

Match IDs with specific prefixes:

{
  "type_id": "starts_with",
  "config": {
    "key": "id",
    "value": "usr_"
  }
}

Matches:

{"id": "usr_12345"}
{"id": "usr_abc"}

Does not match:

{"id": "ord_12345"}
{"id": "12345"}

Case-Insensitive Prefix​

Match protocols regardless of case:

{
  "type_id": "starts_with",
  "config": {
    "key": "url",
    "value": "https://",
    "case_insensitive": true
  }
}

Matches:

{"url": "https://example.com"}
{"url": "HTTPS://EXAMPLE.COM"}
{"url": "Https://Example.com"}

Environment Detection​

Identify production hosts:

{
  "type_id": "starts_with",
  "config": {
    "key": "hostname",
    "value": "prod-"
  }
}

Matches:

{"hostname": "prod-web-01"}
{"hostname": "prod-api-east"}

Does not match:

{"hostname": "staging-web-01"}
{"hostname": "dev-api"}

Exclusion Check​

Match records that do NOT start with a prefix:

{
  "type_id": "starts_with",
  "config": {
    "key": "path",
    "value": "/internal/",
    "not": true
  }
}

Matches:

{"path": "/api/users"}
{"path": "/public/assets"}

Does not match:

{"path": "/internal/admin"}
{"path": "/internal/metrics"}

Nested Field Check​

Check prefixes in nested fields:

{
  "type_id": "starts_with",
  "config": {
    "key": "request.path",
    "value": "/admin/"
  }
}

Matches:

{"request": {"path": "/admin/users"}}
{"request": {"path": "/admin/settings"}}

Log Source Routing​

Route logs by source prefix:

{
  "type_id": "starts_with",
  "config": {
    "key": "source",
    "value": "aws."
  }
}

Matches:

{"source": "aws.cloudwatch"}
{"source": "aws.s3"}
{"source": "aws.lambda"}

Common Patterns​

API Version Routing​

Route different API versions:

V2 API:

{
  "type_id": "starts_with",
  "config": {
    "key": "path",
    "value": "/api/v2/"
  }
}

V1 API (legacy):

{
  "type_id": "starts_with",
  "config": {
    "key": "path",
    "value": "/api/v1/"
  }
}

Multiple Prefix Matching​

Route based on any of several prefixes:

{
  "operator": "or",
  "conditions": [
    {"type_id": "starts_with", "config": {"key": "id", "value": "usr_"}},
    {"type_id": "starts_with", "config": {"key": "id", "value": "org_"}},
    {"type_id": "starts_with", "config": {"key": "id", "value": "team_"}}
  ]
}

Public vs Internal Routes​

Separate public and internal traffic:

Public routes:

{
  "operator": "or",
  "conditions": [
    {"type_id": "starts_with", "config": {"key": "path", "value": "/api/"}},
    {"type_id": "starts_with", "config": {"key": "path", "value": "/public/"}}
  ]
}

Internal routes:

{
  "operator": "or",
  "conditions": [
    {"type_id": "starts_with", "config": {"key": "path", "value": "/internal/"}},
    {"type_id": "starts_with", "config": {"key": "path", "value": "/admin/"}}
  ]
}

Exclude Static Assets​

Filter out static asset requests:

{
  "operator": "and",
  "conditions": [
    {"type_id": "starts_with", "config": {"key": "path", "value": "/static/", "not": true}},
    {"type_id": "starts_with", "config": {"key": "path", "value": "/assets/", "not": true}}
  ]
}

Combined Prefix and Suffix​

Match both beginning and end:

{
  "operator": "and",
  "conditions": [
    {"type_id": "starts_with", "config": {"key": "filename", "value": "report_"}},
    {"type_id": "ends_with", "config": {"key": "filename", "value": ".pdf"}}
  ]
}

Matches:

{"filename": "report_2024.pdf"}
{"filename": "report_quarterly.pdf"}

Service Namespace Routing​

Route by service namespace:

{
  "operator": "and",
  "conditions": [
    {"type_id": "starts_with", "config": {"key": "service", "value": "payment."}},
    {"type_id": "equals", "config": {"key": "environment", "value": "production"}}
  ]
}

Best Practices​

  1. Include delimiters: Include trailing slashes or dots (e.g., /api/ not /api) to avoid partial matches.

  2. Use case_insensitive for URLs: URLs may have inconsistent casing.

  3. Combine with ends_with: For matching both prefix and suffix patterns.

  4. Consider URL encoding: URL paths may contain encoded characters.

  5. Be specific: Longer prefixes are more precise and reduce false matches.

Type Handling​

  • Strings: Direct prefix comparison
  • Numbers: Converted to strings first (e.g., 123 starts with "1")
  • Booleans: Converted to "true" or "false" strings
  • Arrays/Objects: Not supported for direct comparison
  • Missing fields: Returns false (or true if not is set)

Limitations​

  • Simple prefix matching only (no patterns or wildcards)
  • Single prefix per condition (use or for multiple prefixes)
  • No support for matching multiple prefixes in one condition

Troubleshooting​

Not matching expected values:

  • Check for leading whitespace or special characters
  • Verify case sensitivity settings
  • Ensure the full prefix is specified

Unexpected matches:

  • The prefix might be too short
  • Add delimiters to make prefix more specific

Case sensitivity issues:

  • Enable case_insensitive for user-generated content
  • URLs and paths may have mixed casing