query.lab
WASM engineMCP live36 free problems

Ace data interviews by writing real code.

Interview practice for a data scientist

SQLite and Python run right in your browser. Instant grading, no setup, no notebooks.

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Free · no account or card needed

problems
329
problems
company hubs
18
company hubs
learn tracks
6
learn tracks

customers · sample shop data — edit and run

sql · editable
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A taste of the interview

Real questions. A free place to start.

All company hubs

Questions modeled on interviews at

Meta· 12 questionsGoogle· 10 questionsAmazon· 11 questionsNetflix· 10 questionsApple· 18 questions· 8 questionsStripe· 11 questionsAirbnb· 8 questions+ 10 more

why querylab

Everything you need, nothing to install

wasm engine

Your code runs on your machine

SQLite and Pyodide compile to WebAssembly and run in your browser. No servers to wait on, no notebooks to set up.

sql

SQLite

py

Python 3

pd

pandas

Smart result diff

See exactly which rows and cells differ from the expected output.

name · total

Ada · 420

- Linus · 310

+ Linus · 315

3-minute diagnostic

Find your weak spots and get a free 7-day study plan built around them.

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Pro

Practice in your AI assistant

Connect over MCP and pull your next problem without leaving your editor.

Claude DesktopClaude CodeCursorChatGPT developer modeWindsurfVS CodeZed

server: https://querylab.app/mcp

Pro sign-in required. Claude Desktop uses a Node.js bridge.

six tracks

Hands-on coding plus interview theory

code · graded practice

SQL

Joins, aggregation, CTEs and window functions run against a real SQLite database in your browser.

explore

Python

Lists, loops, sets, dicts, functions and generators — graded with hidden unit tests.

explore

Pandas

Filtering, groupby, merges, pivots and reshaping on real DataFrames, powered by Pyodide.

explore

theory · free lessons and quizzes

Machine learning

Models, metrics, bias-variance and overfitting.

A/B testing

Power, p-values, pitfalls and experiment design.

ML system design

Feature stores, serving and monitoring.

Product metrics

North stars, funnels and metric cases.

role pathways

Prep for the job you want

Curated problem sets built around the archetypes each role faces.

Data analyst

Funnels, cohorts, rollups and the SQL product teams ask every week.

view pathway

Data engineer

Joins across sources, reshaping, dedup and pipeline-style transforms.

view pathway

Data scientist

Window functions, pandas analysis and experiment-ready metrics.

view pathway

ML engineer

Production-quality Python plus ML theory and system design.

view pathway

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