UserAgent filter plugin

Parses user-agent strings into structured fields such as browser, operating system, and device. The plugin uses a bundled regex database so it works without any outbound network calls.

• Package: logstash-filter-useragent
• Coverage source: default/bundled
• Official catalog entry: Yes

Plugin overview

useragent is used in the Logstash filter stage. Parses user-agent strings into browser, OS, and device fields.

Typical use cases

• Parse incoming log payloads into structured fields for querying and dashboards.
• Transform fields before indexing to keep schema and naming consistent.

Input and output behavior

• Flow: reads a configured source field and writes parsed/transformed output into a target or root fields.
• Input field: source.
• Output target: controlled by target.
• Important options: source, target, ecs_compatibility, lru_cache_size.

Options

Required

• source (type: string; default: none) — Field that contains the user-agent string.

Optional

• ecs_compatibility (type: string) — Controls ECS field compatibility behaviour (disabled, v1, or v8).
• lru_cache_size (type: number; default: 100000) — In-memory cache size used to speed up repeated lookups.
• prefix (type: string; default: "") — Prefix added to each generated field name.
• regexes (type: string; default: none) — Path to a custom regex YAML file (use the default when possible).
• target (type: string) — Parent field to nest parsed components under (defaults to the event root).

Example configuration

filter {
  useragent {
    source => "[user_agent][original]"
    target => "[user_agent]"
  }
}

Common options configuration

All Logstash filter plugins support these shared options:

• add_field (type: hash; default: {}) — Adds fields when the filter succeeds. Supports dynamic field names and values.
• add_tag (type: array; default: []) — Adds one or more tags when the filter succeeds.
• enable_metric (type: boolean; default: true) — Enables or disables metric collection for this plugin instance.
• id (type: string; default: none) — Sets an explicit plugin instance ID for monitoring and troubleshooting.
• periodic_flush (type: boolean; default: false) — Calls the filter flush method at regular intervals.
• remove_field (type: array; default: []) — Removes fields when the filter succeeds. Supports dynamic field names.
• remove_tag (type: array; default: []) — Removes tags when the filter succeeds.

filter {
  useragent {
    add_field => { "pipeline_stage" => "parsed" }
    add_tag => ["parsed", "logstash_filter"]
    enable_metric => true
    id => "my_filter_instance"
    periodic_flush => false
    remove_field => ["tmp_field"]
    remove_tag => ["temporary"]
  }
}

Apply in Logit.io

1. Open your stack in Logit.io and navigate to Logstash Pipelines.
2. In the filter { ... } section, add a useragent block.
3. Save your pipeline changes, then restart the Logstash pipeline if prompted.
4. Send sample events and verify parsed/enriched fields in OpenSearch Dashboards.

Validation checklist

• Confirm the useragent block compiles without syntax errors.
• Verify expected new/updated fields exist in sample documents.
• Verify unexpected fields are not removed unless explicitly configured.
• Confirm tags added on success/failure align with your alerting and routing rules.

Troubleshooting

• If events are unchanged, verify your filter condition (if ...) matches incoming events.
• If the pipeline fails to start, validate braces/quotes and retry with a minimal filter block.
• If throughput drops, reduce expensive operations and test with representative sample volume.

References

• GitHub package: logstash-filter-useragent (opens in a new tab)
• Canonical catalog: /log-management/ingestion-pipeline/logstash-filters-reference