mastra-ai/mastra · error · Error

Experiment not found: ${experimentIdA}

Error message

Experiment not found: ${experimentIdA}

What it means

compareExperiments fetches both experiments by ID before comparing their scores. This error means the first experiment (experimentIdA) does not exist in the experiments store — getExperimentById returned undefined. It is thrown as a plain Error so the caller can distinguish a bad ID from a comparison failure.

Source

Thrown at packages/core/src/datasets/experiment/analytics/compare.ts:82

  const experimentsStore = await storage.getStore('experiments');
  const scoresStore = await storage.getStore('scores');

  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 } }),
  ]);

View on GitHub (pinned to 75dd419e61)

Solutions

1. Log/verify experimentIdA exists via experimentsStore.getExperimentById({ id: experimentIdA }) before comparing
2. Check you are connected to the same Mastra storage instance that recorded the experiment
3. Re-run the experiment if it was deleted, and compare using the new ID
4. Confirm the ID string has no whitespace/truncation (copy full UUID)

Example fix

// before
await mastra.compareExperiments({ experimentA: staleId, experimentB: idB });
// after
const a = await experimentsStore.getExperimentById({ id: staleId });
if (!a) throw new Error(`Experiment ${staleId} missing; re-run experiment first`);
await mastra.compareExperiments({ experimentA: staleId, experimentB: idB });

const a = await experimentsStore.getExperimentById({ id: experimentIdA });
if (!a) throw new Error(`Experiment A not found: ${experimentIdA}`);

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')) {
    // re-run or re-create the missing experiment
  } else throw err;
}

When it happens

Trigger: Calling compareExperiments({ experimentA, experimentB }) (or the equivalent options object) where the first experiment ID was deleted, never created, or belongs to a different storage backend than the one wired into the Mastra instance.

Common situations: Using an experiment ID from a dev database in a prod environment; an experiment removed by a cleanup/retention job; a typo'd or truncated UUID; storage class swapped (e.g. InMemory store restarted, wiping experiments) between run and compare.

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: ${experimentIdB}
• 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/6f156e63e13ccd9e. Report an issue: GitHub.