Judgment Lab

Case library

Practise the call

Every case asks you to commit an answer and a confidence score before you see what happened. Results go toyour log.

10 cases

Calibration · Week 1

Will this query be slow at 10M rows?

For the user with 400,000 events, roughly how long does this query take?

  • Introductory
  • No AI
  • Example case

databases · indexes · performance

PR review · Week 2

Add CSV export for orders

List every problem you would flag before approving this PR. Give each one a severity: high, medium, or low.

  • Intermediate
  • No AI
  • Example case

authorization · n-plus-one · error-handling

PR review · Week 2

Reserve stock at checkout

List every problem you would flag before approving this PR. Give each one a severity: high, medium, or low.

  • Advanced
  • No AI
  • Example case

concurrency · transactions · idempotency

Kata · Week 3

Four workers, one counter

Before you run anything: what will this program most likely print?

  • Introductory
  • No AI
  • Example case

concurrency · shared-state

Kata · Week 3

How long at 100,000 items?

This takes 0.4 seconds for 10,000 rows. Predict how many seconds it takes for 100,000 rows.

  • Intermediate
  • No AI
  • Example case

performance · complexity · profiling

Design prompt · Week 4

Notifications in six weeks

Choose an approach for the first version. Name the two biggest trade-offs you're accepting, and say what would make you change your mind.

  • Intermediate
  • Example case

messaging · scope · trade-offs

Design prompt · Week 4

Where should the audit log live?

Choose a storage approach for the audit log. What are you giving up, and which part of your decision is hardest to reverse?

  • Advanced
  • Example case

data-modeling · storage · reversibility

Incident replay · Week 5

Retry storm after a cache outage

The cache recovered within a minute, but the API is still failing 20 minutes later. What is keeping it down, and what would you do first to bring it back?

  • Intermediate
  • No AI
  • Example case

caching · retries · load

Incident replay · Week 5

Latency creep hours after a routine deploy

Checkout latency is climbing hours after a deploy, while CPU and database load look normal. What is your leading hypothesis, and what do you do in the next 15 minutes?

  • Advanced
  • No AI
  • Example case

connection-pools · resource-leaks · observability