mastra-ai/mastra · error · Error

Experiment not found: ${experimentIdB}

Error message

Experiment not found: ${experimentIdB}

What it means

compareExperiments fetches both experiments by ID; this error means the SECOND experiment (experimentIdB) was not found in the experiments store. Identical semantics to the experimentIdA variant but reported for the B argument.

Source

Thrown at packages/core/src/datasets/experiment/analytics/compare.ts:85

  if (!experimentsStore) {
    throw new Error('ExperimentsStorage not configured.');
  }
  if (!scoresStore) {
    throw new Error('ScoresStorage not configured.');
  }

  // 2. Load both experiments
  const [experimentA, experimentB] = await Promise.all([
    experimentsStore.getExperimentById({ id: experimentIdA }),
    experimentsStore.getExperimentById({ id: experimentIdB }),
  ]);

  if (!experimentA) {
    throw new Error(`Experiment not found: ${experimentIdA}`);
  }
  if (!experimentB) {
    throw new Error(`Experiment not found: ${experimentIdB}`);
  }

  // 3. Check version mismatch
  const versionMismatch = experimentA.datasetVersion !== experimentB.datasetVersion;
  if (versionMismatch) {
    warnings.push(
      `Experiments have different dataset versions: ${experimentA.datasetVersion} vs ${experimentB.datasetVersion}`,
    );
  }

  // 4. Load results for both experiments
  const [resultsA, resultsB] = await Promise.all([
    experimentsStore.listExperimentResults({ experimentId: experimentIdA, pagination: { page: 0, perPage: false } }),
    experimentsStore.listExperimentResults({ experimentId: experimentIdB, pagination: { page: 0, perPage: false } }),
  ]);

  // 5. Load scores for both experiments
  const [scoresA, scoresB] = await Promise.all([

View on GitHub (pinned to 75dd419e61)

Solutions

1. Verify experimentIdB exists with experimentsStore.getExperimentById({ id: experimentIdB }) before comparing
2. Re-run the baseline experiment to obtain a fresh ID if it was deleted
3. Ensure both IDs come from the same Mastra storage instance/environment
4. Fix typos or truncated IDs in the comparison call

Example fix

// before
await mastra.compareExperiments({ experimentA: idA, experimentB: config.baselineId });
// after
const baseline = await experimentsStore.getExperimentById({ id: config.baselineId });
if (!baseline) throw new Error(`Baseline experiment ${config.baselineId} not found; re-run it first`);

const b = await experimentsStore.getExperimentById({ id: experimentIdB });
if (!b) throw new Error(`Experiment B (baseline) not found: ${experimentIdB}`);

function isExperiment(e: unknown): e is NonNullable<Awaited<ReturnType<typeof experimentsStore.getExperimentById>>> {
  return !!e && typeof e === 'object' && 'id' in e;
}

try {
  await mastra.compareExperiments({ experimentA, experimentB });
} catch (err) {
  if (err instanceof Error && err.message.startsWith('Experiment not found')) {
    // recreate baseline experiment, then retry
  } else throw err;
}

When it happens

Trigger: Calling compareExperiments with a valid experimentA but an experimentB ID that does not exist (deleted, wrong environment, typo, or written to a different storage backend).

Common situations: Comparing against a 'baseline' experiment ID hardcoded in config that was cleaned up; baseline recorded before a storage migration; baseline ID from another project.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Experiment not found: ${experimentIdA}
• EXPERIMENT_NOT_FOUND
• EXPERIMENT_TARGET_NOT_FOUND
• DATASET_NOT_FOUND
• Dataset not found: ${args.id}

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/687b48254080f4f9. Report an issue: GitHub.