How TanStack Query caches, deduplicates, prefetches, and rolls back
Many of the big decisions in a React frontend come down to where data lives and when you fetch it. This quiz starts with the split between server state (a cached copy of data...
Quizzes
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How web apps keep you logged in: sessions, JWTs & refresh tokens
How do web apps keep you logged in, and how do they log you out? This quiz compares server-side sessions with stateless JWTs, then covers what follows from that choice: where...
HTTP API design: methods, status codes, pagination, and errors
Many APIs called REST are really RPC over HTTP. This quiz covers the choices that matter once other developers build against your endpoints: safe and idempotent methods, PUT...
HTTP caching from the browser to the CDN to React Query
Follow one request outward through every cache it can hit: the browser's HTTP cache (Cache-Control, ETag, Last-Modified, revalidation), the CDN edge, the client query cache...
Infrastructure you walk past
A photo-based field guide to the machinery on every street corner: transformers, cutouts, cell sites, hydrants, backflow preventers, cathodic protection posts, manhole covers,...
LLM mechanics: tokens, context, and cost
A practical quiz about how LLM APIs handle tokens, context, sampling, caching, streaming, structured output, and knowledge cutoffs. It includes production scenarios and cost...
Making retries safe: idempotency keys, backoff, and dead-letter queues
Networks fail in the middle of requests, so real systems retry, and retries are where duplicate charges and lost messages come from. Learn the difference between at-least-once,...
Map projections: every flat map distorts
See why flattening a globe always distorts it, how Tissot's indicatrix reveals local distortion, and why the shortest flight path can look curved on a map. You will not need to...
Master JavaScript promises & async execution
Step through the event loop, microtask & macrotask queues, async/await suspension, and tricky async patterns. Detailed MDN-linked explanations reveal after every answer.
MCP and tool calling: the failure modes the docs warn about
Forty-two questions on how tool-using agents break: tool and schema design, the agent loop and when it should stop, parallel versus sequential calls, retries and idempotency,...
Names that break software: NULL, True and little Bobby Tables
A man picks the licence plate NULL and ends up with $12,049 in strangers' parking fines. A woman named Null can't book a flight online. An actor named True gets locked out of...
Network waterfalls: request stages, preload hints and HTTP/2
The network panel shows why your page is slow, once you know how to read it. This quiz walks through the bars: what each segment of a request means, which requests block...