If you're generating test data today, you've probably landed on one of
three approaches: click through a UI like Mockaroo, pull in a library
like Faker.js and write generation code yourself, or call a hosted API
like JsonFabrica. Comparing these test data generation tools side by
side, the real differences aren't about which one produces "better"
fake data — Faker.js, Mockaroo, and JsonFabrica are all capable of
that. The differences are about where the tool lives, how it handles
relationships between records, and who's responsible for running it.
Three test data generation tools compared, shape by shape
Mockaroo is a browser-based UI: you define columns and types through a
web form, preview rows, and export a file — or hit its API directly,
which is available even on the free tier (paid tiers raise the volume
ceiling rather than gate API access itself). Faker.js is a JavaScript
library: you import it into your own code and call functions like
faker.person.fullName() or
faker.internet.email() to build up objects yourself, one field at a
time. JsonFabrica is an API-first hosted service: you send a schema (or
use a template) to an endpoint and get structured, schema-conformant
JSON back, with no UI step and no library to install in your own
codebase.
That distinction matters more than it sounds. A UI tool is something a
person operates by hand. A library is something a developer owns and
maintains inside their own project — you write the loops, the
relationships, the edge cases. An API-first tool is infrastructure:
something your CI pipeline, your seed script, or an AI coding agent can
call directly, without a human in the loop or generation logic living
in your repo.
UI vs. library vs. API, in practice
Mockaroo's UI is genuinely fast for a one-off task — sketch a schema,
click generate, download a CSV or JSON file. What it isn't built for is
wiring generation into an automated pipeline where nobody is clicking
anything. Its API can cover that, but at free-tier volumes (200
requests/day, up to 1,000 rows per call) it's still built around the
UI-first workflow — for heavier automated use, you either pay for more
API volume or reach for a Mockaroo alternative built API-first from the
start.
Faker.js sits at the opposite end. It's a library, not a service, so
there's no hosting, no account, and no network call — you generate data
in-process, in whatever language your project already uses (there are
Faker ports for several languages — the original Faker was a Perl
library, later ported to Ruby, PHP, Python, Java, and others; Faker.js
is itself one of those ports, not the original). The tradeoff is that
Faker.js gives you field generators, not a data model. If you want an order that references a
real customer ID, or a set of line items that sum to the order total,
you write that logic yourself, by hand, in every project that needs it.
JsonFabrica's tradeoff is the mirror image: you don't write generation
logic, because the schema (or a prebuilt template) describes what you
want and the service produces it, relationships and all. What you give
up is the "no dependency" simplicity of a library — you're calling a
hosted API instead of importing a package.
Schema and relational data support
This is where the three tools diverge most. Faker.js has no concept of
a schema or a relationship between generated objects — it's a toolbox
of individual field generators, and any structure across records
(foreign keys, consistent totals, matching timestamps) is code you
write and maintain. Mockaroo lets you define a schema per dataset and
has some support for relating fields within a single generation, but
it's still fundamentally a spreadsheet-shaped tool: one flat schema,
one export, one dataset at a time.
JsonFabrica is schema-driven and template-based generation by design,
not an add-on. You describe the shape of a record — or reference a
template — and the engine fills it in against real-world patterns
rather than pure randomness, so an order's shipped_at comes after its
created_at, and a discount_code points at a code that actually
exists. Referential integrity across related records — customers that
own orders, orders that own line items — is handled by the generation
engine itself, not left to your seed script to stitch together after
the fact.
JsonFabrica also has stateful sequence functions (createSeq /
getSeq) for cases where you need collision-free unique IDs or
incrementing values across separate test runs — something neither a
stateless library like Faker.js nor a per-export UI tool like Mockaroo
is built to track between calls.
Hosted vs. self-run
Faker.js runs entirely inside your own process — no network dependency,
no data leaving your machine, no bill. That's a real advantage if
you want full control and zero external dependencies for a CI job. The
cost is that you own everything: version upgrades, keeping generation
logic consistent across projects, and building relational logic
yourself if you need it.
Mockaroo is hosted, but its primary interface is the UI; its API is
available free, and paid tiers raise how much you can pull through it
rather than unlocking API access itself. JsonFabrica is hosted and
API-first from the ground up — every feature the UI could offer is available as
an HTTP call, described in a published OpenAPI spec, so it fits into a
CI pipeline or seed script the same way any other API dependency does.
JsonFabrica also ships an MCP server, so AI coding agents in tools like
Claude Desktop or Cursor can request schema-conformant test data
directly in a session, without a person switching to a browser tab.
The tradeoff for going hosted is the one you'd expect: you depend on an
external service being up, and usage is metered — JsonFabrica bills on
a credit-based model rather than a flat license, so cost scales with
how much data you actually generate.
Picking between them
If you need a quick, one-off dataset and don't mind a manual export, a
UI-based tool like Mockaroo is fast and low-friction. If you want
individual fake field values inside code you already control, and
you're fine writing your own relational logic, Faker.js is a solid,
zero-dependency Faker.js alternative — arguably the default choice for
in-process unit tests. If you need schema-conformant, relationally
consistent test data as part of an automated pipeline, seed script, or
AI agent workflow — without hand-writing the logic that keeps records
consistent with each other — that's the gap JsonFabrica is built to
fill: an API-first, schema-driven service with referential integrity
and sequence functions built in, rather than bolted on after the fact.
FAQ
Is Mockaroo free to use?
Yes — Mockaroo's free tier covers the UI and direct API access, capped at
200 requests per day and up to 1,000 rows per call. Paid tiers raise those
volume limits rather than unlocking API access itself.
Is Faker.js the original Faker library?
No. The original Faker was a Perl library, later ported to Ruby, PHP,
Python, Java, and other languages. Faker.js is the JavaScript port of that
same lineage, not the original implementation.
Can Faker.js generate related records, like an order linked to a real customer ID?
Not by itself. Faker.js is a toolbox of individual field generators with no
concept of a schema or a relationship between generated objects — wiring a
foreign key or keeping totals consistent across records is code you write
and maintain yourself, which is exactly the gap schema-driven tools like
JsonFabrica close.
Does JsonFabrica have a free plan or trial?
JsonFabrica's Starter plan includes a 30-day free trial. A
valid payment method is required at signup, but you're not charged until
the trial converts; Growth and Business plans bill immediately with no
trial.
None of these tools are strictly better than the others across the
board. They're built for different points in the workflow, and the
right choice depends on whether you're clicking through a one-off
export, writing generation code by hand, or wiring test data into a
pipeline that has to run without anyone watching it.
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