URL Decode filter plugin

Decodes URL-encoded (percent-encoded) values so escaped characters become readable text. Useful when upstream systems log encoded URLs or form data.

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

Plugin overview

urldecode is used in the Logstash filter stage. Decodes URL-encoded field values.

Typical use cases

• Tag failed operations and route them to dedicated troubleshooting views.
• Transform fields before indexing to keep schema and naming consistent.

Input and output behavior

• Flow: reads one or more configured fields, applies plugin logic, then updates event fields in place.
• Input field: field (default: "message").
• Output: updates the current event in place unless configured otherwise.
• Important options: field, tag_on_failure, all_fields, charset.
• Failure signaling: uses tag_on_failure (default: ["_urldecodefailure"]) so failed events can be routed or inspected.

Options

Required

• No required plugin-specific options.

Optional

• all_fields (type: boolean; default: false) — When true, decode every string field in the event.
• charset (type: string; default: "UTF-8") — Character set used when interpreting decoded bytes (for example UTF-8).
• field (type: string; default: "message") — Field to decode.
• tag_on_failure (type: array; default: ["_urldecodefailure"]) — Tags applied when decoding fails.

Example configuration

filter {
  urldecode {
    field   => "[url][query]"
    charset => "UTF-8"
    tag_on_failure => [ "_urldecodefailure" ]
  }
}

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 {
  urldecode {
    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 urldecode 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 urldecode 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.
• Check for tag_on_failure tags (default: ["_urldecodefailure"]) to quickly isolate parse/mutation failures.
• If throughput drops, reduce expensive operations and test with representative sample volume.

References

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