Rowsmith

Rowsmith

Fake test data from a table schema, as CSV, JSON or SQL INSERTs. Free and rate-limited, with no account and no API key.

For fixtures, seed data, demos and CI. Send a schema, get rows back.

Quickstart (60 seconds)

1. Add Rowsmith to Claude Desktop, Cursor or another MCP client:

{"mcpServers":{"rowsmith":{"command":"npx","args":["-y","rowsmith-mcp"]}}}

2. Ask: Generate 20 orders with a fixed seed as CSV

3. Or call the API directly:

curl -s https://testdata-api.re-jam620.workers.dev/v1/generate -H 'content-type: application/json' \
  -d '{"rows":20,"seed":42,"format":"csv","columns":[{"name":"order_id","type":"sequence","prefix":"ord_","pad":4},{"name":"email","type":"email"},{"name":"total_usd","type":"decimal","min":1,"max":500}]}'

curl -s 'https://testdata-api.re-jam620.workers.dev/v1/invalid?kind=email&count=5&seed=42'

ID=$(curl -s https://testdata-api.re-jam620.workers.dev/v1/sandbox -H 'content-type: application/json' -d '{"seed":42}' | sed -E 's/.*"id":"([^"]+)".*/\1/')
curl -s https://testdata-api.re-jam620.workers.dev/v1/sandbox/$ID/charges -H 'content-type: application/json' \
  -d '{"amount":1999,"currency":"usd","card":"4242424242424242"}'

Python's standard-library urllib is blocked by Cloudflare before it reaches the API (403, error code 1010) when it sends its default User-Agent. Set your own, e.g. User-Agent: my-tests/1.0. In our tests on 2026-10-18, requests, httpx, aiohttp, Node and curl worked with their defaults.

• Free, rate-limited, no account, no API key.
• The same schema and seed give byte-identical output for the same generator version.
• An invalid-values catalogue with the reason each value is invalid.
• A payment sandbox that never moves money: a sandbox and everything in it is deleted 1 hour after it is created. It accepts only card numbers from Stripe's published testing list and stores no free text you send.
• Listed on the official MCP Registry as io.github.meiorz/rowsmith.

Try it

curl -s https://testdata-api.re-jam620.workers.dev/v1/generate \
  -H 'content-type: application/json' \
  -d '{"table":"orders","rows":3,"seed":42,"format":"csv","columns":[{"name":"order_id","type":"sequence","prefix":"ord_","pad":4},{"name":"email","type":"email"},{"name":"total_usd","type":"decimal","min":1,"max":500},{"name":"status","type":"enum","values":["paid","refunded","partially_refunded"],"weights":[8,1,1]}]}'

What comes back

order_id,email,total_usd,status
ord_0001,amara.weber561@mail.test,230.25,paid
ord_0002,maya.wang873@mail.test,17.04,paid
ord_0003,jin.weber19@mail.test,92.51,paid

That request, run now by the service itself. The same schema and seed give byte-identical output for the same generator version (generator 1, sfc32-splitmix32, sent as x-generator-version), so a CI run is reproducible.

Use it from an AI agent

The rowsmith-mcp server gives MCP clients a generate_test_data tool. It is listed on the official MCP Registry as io.github.meiorz/rowsmith.

{
  "mcpServers": {
    "rowsmith": { "command": "npx", "args": ["-y", "rowsmith-mcp"] }
  }
}

For more than about 50 rows, the tool can write a file instead of putting the data in the model's context.

Column types

• uuid
• sequence
• integer
• decimal
• boolean
• enum
• date
• datetime
• first_name
• last_name
• full_name
• email
• phone
• test_card
• ssn_invalid
• iban_invalid
• text

Options per type: /v1/types. Full request schema: /openapi.json.

What the data is

• Every value is generated by a program from a seed. No real person's data is used as input, and no record is derived from a real person.
• Identifiers come only from reserved or invalid ranges: example.com, example.org, example.net and.test email domains; 555-0100 to 555-0199 phone numbers; card numbers published for testing; SSN-shaped and IBAN-shaped values in ranges that can never be valid.
• A generated name can still match a real person's by chance.
• Send schemas only, never real data.

Limits

Up to 500 rows and 50 columns per call, with daily limits per caller (200) and overall. Over a limit you get HTTP 429 with Retry-After. The current limits are in /openapi.json.