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Rate Limit Node ​

Purpose & Use Cases ​

The rate-limit node enforces a minimum interval between output messages based on external timestamps (from hardware, sensors, or other sources) rather than internal Date.now() timing. This makes rate decisions immune to event-loop drift and more accurate for real-time data streams.

Typical scenarios:

  • Throttle high-frequency sensor or camera data to a manageable rate
  • Deduplicate rapid-fire hardware triggers that arrive faster than processing can handle
  • Control output cadence for downstream systems with rate constraints
  • Monitor message timing statistics across a rolling window

Input/Output Specification ​

Inputs ​

  • Incoming Message: Any Node-RED message containing a timestamp at the configured path.

Outputs ​

  • Output 1 (passed): Messages that meet or exceed the minimum interval since the last accepted message. The first message always passes.
  • Output 2 (throttled): Messages that arrived sooner than the configured interval since the last accepted message.

Both outputs receive timing data at the configured output path (when set).

Timing Data ​

javascript
{
  timeBetween: number,      // ms since last accepted message (-1 for first message)
  avgTimeBetween: number,   // average ms between messages in the rolling window (rounded)
  messageCount: number      // number of messages currently in the rolling window
}

Configuration Options ​

Timestamp ​

  • Type: Typed input (msg | flow | global)
  • Default: msg.timestamp
  • Purpose: Path to the external timestamp value. Accepts ISO 8601 strings, epoch milliseconds, or Date objects.

Interval (ms) ​

  • Type: Typed input (num | msg | flow | global)
  • Default: 250
  • Purpose: Minimum milliseconds between passed messages. Messages arriving sooner are sent to the throttled output.

Window (ms) ​

  • Type: Typed input (num | msg | flow | global)
  • Default: 5000
  • Purpose: Rolling time window for average cadence calculation. Messages older than this are dropped from the history.

Output to ​

  • Type: Typed input (msg | flow | global)
  • Default: (empty -- no timing data attached)
  • Purpose: Where to write the timing data object on each message.

Behavior ​

  • The first message always passes (timeBetween = -1).
  • Subsequent messages pass only if the external timestamp difference from the last accepted message meets or exceeds the interval.
  • All messages (passed and throttled) are added to the rolling window history for cadence calculation.
  • The rolling window is pruned on each message to remove entries older than the window size.
  • Invalid timestamps cause the message to be dropped with a warning.
  • Invalid interval or window values cause the message to be dropped with a warning.
  • Interval and window size can be set dynamically per-message when using msg, flow, or global types.

Status ​

  • Blue dot -- Idle, no messages received yet.
  • Green dot -- Last message passed. Shows time since previous and rolling average.
  • Yellow dot -- Last message was throttled. Shows the interval comparison.
  • Red ring -- Error (invalid timestamp, interval, or window value).

Example Flows ​

Throttle Camera Frames ​

[Camera] → [Rate Limit: interval=100, timestamp=msg.captureTime] → [Process Frame]

Accept at most one frame every 100ms based on the camera's own capture timestamp.

Monitor Sensor Cadence ​

[Sensor] → [Rate Limit: interval=0, output=msg.timing] → [Dashboard]

Pass all messages through (interval=0) while attaching rolling timing statistics for monitoring.