Bug: addDimensions() is one dimension more restrictive than addDimension() at the boundary

[svozza]

Expected Behavior

addDimension() and addDimensions() should enforce the same maximum dimension limit. When there are 28 dimensions and a user adds 1 more, both methods should either allow or reject it consistently.

Current Behavior

addDimension() uses <= (Metrics.ts:250):

if (MAX_DIMENSION_COUNT <= this.#dimensionsStore.getDimensionCount()) {

addDimensions() uses >= (Metrics.ts:285):

if (currentCount + newSetCount >= MAX_DIMENSION_COUNT) {

At the boundary (28 existing dimensions, adding 1 more to reach the MAX_DIMENSION_COUNT of 29), addDimension() allows it but addDimensions() throws a RangeError.

Code snippet

import { Metrics, MetricUnit } from '@aws-lambda-powertools/metrics';

const metricsA = new Metrics({ namespace: 'test' });
const metricsB = new Metrics({ namespace: 'test' });

// Fill both to 28 dimensions (1 default "service" + 27 regular)
for (let i = 1; i < 28; i++) {
  metricsA.addDimension(`dimension-${i}`, 'test');
  metricsB.addDimension(`dimension-${i}`, 'test');
}

// ✅ addDimension allows the 29th dimension
metricsA.addDimension('final', 'test');

// ❌ addDimensions rejects the 29th dimension
metricsB.addDimensions({ final: 'test' });
// RangeError: The number of metric dimensions must be lower than 29

Steps to Reproduce

1. Create a Metrics instance (which auto-adds service as a default dimension)
2. Add 27 dimensions via addDimension() to reach 28 total
3. Call addDimensions({ final: 'test' }) to add the 29th
4. Observe RangeError — while addDimension('final', 'test') would have succeeded

Possible Solution

Change the >= to > in addDimensions() at Metrics.ts:285 to match the behavior of addDimension():

if (currentCount + newSetCount > MAX_DIMENSION_COUNT) {

Powertools for AWS Lambda (TypeScript) version

2.33.0

AWS Lambda function runtime

22.x

Packaging format used

npm

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Disclaimer: After creating an issue, please wait until it is triaged and confirmed by a maintainer before implementing it. This will reduce amount of rework and the chance that a pull request gets rejected.

[dreamorosi]

Wow that's not great - how did you find this? Good catch!