claude-skills/tinybird-best-practices/rules/mock-data.md

Mock Data Generation

Tinybird mock data flow (as implemented by the agent) for a datasource:

1. Build a SQL query that returns mock rows.
2. Execute locally with a limit and format using tb --output=json|csv '<sql>' --rows-limit <rows> command.
3. Preview the generated output.
4. Confirm creation of a fixture file under fixtures/.
5. Write the fixture file:
   • fixtures/<datasource_name>.ndjson or fixtures/<datasource_name>.csv
6. Confirm append.
7. Append the fixture to the datasource in Tinybird Local.

Example Mock Query

SELECT
    rand() % 1000 AS experience_gained,
    1 + rand() % 100 AS level,
    rand() % 500 AS monster_kills,
    concat('player_', toString(rand() % 10000)) AS player_id,
    rand() % 50 AS pvp_kills,
    rand() % 200 AS quest_completions,
    now() - rand() % 86400 AS timestamp
FROM numbers(ROWS)

Notes:

• The query must return exactly ROWS rows via FROM numbers(ROWS).
• Do not add FORMAT or a trailing semicolon in the mock query itself.

Error Handling Notes

• If the datasource is in quarantine, query <datasource_name>_quarantine and surface the first 5 rows.
• If append fails with "must be created first with 'mode=create'", rebuild the project and retry.