Math filter plugin

Applies basic arithmetic operations to numeric fields. Use it to compute derived metrics (for example converting milliseconds to seconds) directly inside the pipeline. This plugin is not part of the default Logstash distribution; it is pre-installed on Logit stacks.

• Package: logstash-filter-math
• Coverage source: explicitly installed in the Logit image
• Official catalog entry: No

Plugin overview

math is used in the Logstash filter stage. Applies arithmetic operations to numeric fields.

Typical use cases

• Transform fields before indexing to keep schema and naming consistent.
• Prepare high-quality fields for alerts, dashboards, and downstream pipelines.

Input and output behavior

• Flow: processes matching events and mutates fields/tags within the same event.
• Input: works on events that match your surrounding if conditions.
• Output: updates the current event in place unless configured otherwise.

Options

Required

• No required plugin-specific options are defined.

Optional

• This plugin has no plugin-specific options; use the shared filter options documented below.

Example configuration

filter {
  math {
    calculate => [
      [ "[http][response][time_ms]", "/", "1000.0", "[http][response][time_seconds]" ]
    ]
  }
}

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 {
  math {
    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 math 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 math 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-math (opens in a new tab)
• Canonical catalog: /log-management/ingestion-pipeline/logstash-filters-reference