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Mock Service Worker vs Gretel.ai

Feature checklists rarely decide anything. What decides it is the pricing metric, who has to write the tests, and which limitation you can live with.

Mock Service WorkerTest Data & Mocks
Gretel.aiTest Data & Mocks

Entry price

Free and open source

Open source

Quote on request

Quote only

What drives the bill

The metric that actually scales your invoice.

Free and open source. You pay in engineering time and CI minutes.

The old credit-based self-serve tier is gone. The successor microservices are licensed through NVIDIA AI Enterprise; NeMo Data Designer can be tried on build.nvidia.com.

Free tier

Everything, self-hosted

Open source

MIT

Self-hostable

No-code authoring

Languages

JavaScriptTypeScript
PythonCodeless

Platforms

WebAPI
API

Fits teams

Solo / side projectStartupScale-up / mid-marketEnterprise
Enterprise

Adoption

Category standard

OSS community · since 2020

Emerging

NVIDIA (formerly Gretel) · since 2019

Strengths

  • One set of handlers reused across unit, component, E2E and local development.
  • Application code is completely unaware it is being mocked — no test-only branches.
  • Supports REST and GraphQL with the same model.
  • Formal differential-privacy guarantees rather than best-effort masking, now via DP-SGD in NeMo Safe Synthesizer.
  • Synthetic data preserves statistical relationships useful for analytics and model training.
  • Backed by NVIDIA's platform investment rather than a single startup's runway.

Limitations

  • JavaScript ecosystem only.
  • Service Worker registration adds a setup step and occasional caching confusion.
  • Handlers can drift from the real API without contract verification.
  • No longer buyable as Gretel — you are procuring NVIDIA AI Enterprise, which is far heavier than the old self-serve signup.
  • Model training adds time and cost compared to rule-based masking.
  • Safe Synthesizer trains on a real dataset, so it does not help with greenfield data that does not exist yet.

Best for

Front-end teams that want one mocking approach across every kind of test.

Regulated enterprises already standardising on NVIDIA AI Enterprise. Teams that wanted Gretel's self-serve tier should look at Tonic or Neosync instead.

Full review
Full review

Pricing last reviewed August 2026 and is indicative only — confirm on each vendor’s own page.