Explore
Every result on the site. Arena entries open the live side-by-side builds; bench entries open the graded trial with its diffs.
Beam Deflection Studio
Build an inspectable beam deflection studio with load cases, reactions, shear, moment, and deflection views.
Building Drift Dashboard
Create a building drift dashboard for comparing story drift, demand ratios, and limit-state status across floors.
Response Spectrum Explorer
Create a response-spectrum explorer that compares seismic inputs, damping assumptions, and structural response views.
Structural Vibration Lab
Build a structural vibration lab for inspecting modal behavior, forcing input, and response over time.
Rotating Machinery Vibration Analyzer
Build a rotating machinery vibration analyzer with speed, spectrum, fault signatures, and diagnostic cues.
Executive Analytics
Build an executive analytics dashboard with KPI scorecards, trends, operating signals, and decision-ready summaries.
Fatigue Life Estimator
Create a fatigue life estimator that presents stress ranges, S-N assumptions, damage accumulation, and life projections.
Groundwater Flow Lab
Build a groundwater flow lab for inspecting aquifer parameters, hydraulic gradient, drawdown, and flow-field behavior.
Museum Heist
Create a playable museum heist browser game with stealth, guarded rooms, collectibles, and clear win/loss feedback.
NovaOS Dashboard
Design a NovaOS dashboard with system widgets, live status panels, productivity controls, and polished app-shell behavior.
Tuned Mass Damper Playground
Build an interactive tuned mass damper playground: a swaying tower with an adjustable TMD, showing how mass ratio and tuning tame the response.
01 — Interval scheduler bug hunt
A maintenance-window scheduler with three planted regressions - a missed adjacency merge, a subtract() that applies only the first hole, and a gap finder that ignores t=0 and crashes on an empty calendar. Docstrings are the contract; 6 of 19 tests fail at the start.
02 — Sliding-window rate limiter
Implement SlidingWindowLimiter from a written contract: weighted requests, per-key isolation, exact expiry boundaries, retry_after arithmetic - all against an injected clock. Every one of the 14 tests starts red.
03 — Calendar recurrence expansion
An RRULE-style expand(): DAILY/WEEKLY/MONTHLY with intervals, Monday-based week buckets, BYDAY and BYMONTHDAY (-1 = last day), leap Februaries and skipped short months. No stdlib shortcut exists. 17 tests from zero.
04 — Async task pool
Implement createTaskPool from a written contract: a concurrency limit, priority scheduling with FIFO ties, three distinct AbortSignal behaviours (pre-aborted, aborted-in-queue, aborted-in-flight), live size/pending counters and onIdle(). Deterministic - no timers, only settled promises.
05 — Delimited-text codec repair
Classic 1-based Delphi string code with three planted regressions: a trim that eats tabs it must preserve, a quote-escape that consumes one character too few, and a dropped trailing empty field. Compiled with dcc32 and run as a native Win32 console suite.
06 — Deterministic topo-sort
Kahn's algorithm with ordinal tie-breaking, plus shortest-cycle extraction with normalized reporting: start at the smallest node, follow edge direction, break length ties lexicographically. The discipline is entirely in the tie-break and normalization rules.
07 — Checkout package repair
Five modules, six interacting regressions: banker's rounding where half-up is specified, a cart that duplicates lines instead of merging and leaks its internals, discounts applied in listed order without the zero floor, and tax computed before discounts. The receipt is only right when every module is.
08 — Undo/redo event store
createStore with undo/redo, branching history, an eviction cap, and transactions that batch into one undo step, roll back on throw, and flatten when nested. Object.is no-ops must leave no trace, and listeners get snapshot semantics plus a reentrancy guard.
09 — Log query engine
A query language with NOT > AND > OR, implicit AND, parentheses, quoted phrases with escapes, prefix wildcards, and a full FormatException lattice for malformed input. Parser discipline, not parsing tricks.
10 — Pipeline rescue
The package won't even import - and the error it raises ('data source missing') is a lie, planted by an over-broad exception wrapper that swallows a circular import. Diagnose past the misleading symptom, untangle the modules, then fix two logic bugs the crash was hiding.
11 — Schema validator
A mini schema engine where the product is the error report: exact paths ($.users[2].id), exact codes, exact sorting, no descent past a wrong type, bool-is-not-int, open vs closed objects. Validation is easy; reporting exactly right is the task.
12 — URL router
Static, :param and *wildcard segments with static > param > wildcard precedence decided left-to-right, percent-decoding for captures only, trailing-slash tolerance, and the 404-versus-405 distinction with a sorted Allow list.
13 — Fixed-width sales report
Byte-exact golden strings: three aligned columns, first-seen region grouping, subtotals and a grand total, hand-rolled thousands separators, product truncation with '..'. Every test compares the whole report string character by character.
14 — Template engine
{{name}} with dotted paths, {{#each}} with scope chains and {{.}}, {{#if}}/{{else}} with a truthiness table, escaping, and a structural-error lattice - missing keys throw in substitutions but are simply false in conditionals.
15 — Formula evaluator
An Int64 expression parser: precedence with repeatable unary minus, division truncating toward zero, remainder with the dividend's sign, overflow detection on literals and every operation, and distinct zero/overflow/syntax error classes.
16 — Search under a probe budget
The starter is already correct: linear scans that pass every behaviour test. But the suite meters every probe - hard logarithmic call budgets, no duplicate reads, no out-of-range probes - so the task is making the code efficient without breaking a single edge case.
17 — Event-time window aggregator
Hopping event-time windows driven only by pushed timestamps: watermark advancement, allowed lateness, exclusive window ends, multi-window membership, gap events that belong nowhere, ascending emission, and a flush that finalizes the stream. Every count lands in stats.
18 — Binary frame codec
A framed wire format over raw bytes: big-endian lengths, a Fletcher-16 checksum, and a resynchronizing stream decoder that must skip garbage, reject false headers, and count bad checksums and truncated tails - byte-exact against golden frames.
19 — Unified-diff patch applier
A strict unified-diff subset: exact hunk headers, marker and count validation, ascending-hunk enforcement, context matching that names the failing hunk, pure insertions anchored at line zero, and reverse application that un-applies a patch.
20 — Version constraint resolver
Semver-lite ranges (caret pins the leftmost non-zero component) over a text registry, resolved to the highest admissible versions by a normative backtracking order - including a diamond conflict that forces the solver to abandon its first greedy choice.
21 — Approval workflow repair
A five-state approval workflow with three planted regressions: an inclusive tier boundary turned exclusive, illegal transitions mislabelled DENY in the audit log, and a withdrawal hole in the Approved state. The audit transcript is compared line by line.
22 — Virtual-DOM reconciler
A normative diff: text/replace/set/unset/insert/remove/move ops compared literally, keyed reconciliation with a working-copy walk, alphabetical prop ordering, sequential path semantics - plus a pure apply() that must reproduce the new tree without mutating anything.
23 — CSS cascade resolver
Selector parsing (compounds, > and descendant combinators, attribute tests, comma lists), specificity as (ids, classes+attrs, types), !important, source order, and matching that must backtrack across candidate ancestors. The computed style is compared key by key.
24 — Contrast toolkit repair
A WCAG contrast toolkit with three planted regressions: shorthand hex expanded by sixteens instead of duplication, a contrast ratio that forgets to put the lighter luminance on top, and AAA large-text grading that ignores the large flag. Real formulas, real constants.
25 — HTML sanitizer
A whitelist sanitizer over a strict tag grammar: script and style swallowed with their content, URL scheme policy on href/src, attribute whitelists with fixed output order, entity-blind escaping, and stack-based repair of mis-nested and unclosed markup.
26 — Flexbox-lite layout
Greedy line packing with gap arithmetic, integer growth distributed by largest remainder with leftmost tie-breaks, per-line heights and top-aligned stacking - every X, Y, W, H asserted exactly, including a golden two-line scenario.
27 — Markdown renderer
A Markdown subset rendered byte-exactly: single-line headings, all-dash lists, fenced code with language classes and trailing newlines, a normative inline scan (code spans, bold containing italic, links with parsed labels), and HTML that never passes through unescaped.
28 — Chunk-proof stream scanner
A feed()/finish() scanner whose event stream must be identical for every way of splitting the same document - the suite replays adversarial cuts (mid-escape, between CR and LF) plus thirty fixed-seed fuzz chunkings, and a normative emission law pins exactly which feed() call returns each event.
29 — Report formatter refactor
The starter already works: a legacy formatReport whose bytes are locked by regression tests that pass on day one. Grow it into a composable createFormatter/with() API with module-level defaults the legacy entry point must honor too - strict where new, lenient where old, identical bytes throughout.
30 — Bytecode stack machine
A fifteen-opcode stack VM whose product is its execution trace: step numbers, instruction pointers, post-instruction stacks, one exactly-formatted line each. Int64-checked overflow, toward-zero division, call/ret with depth caps, and eight distinct fault codes that must end the trace on the right line.
31 — Three-way text merge
diff3-lite from a normative LCS: suffix DP with a pinned tie-break, two alignments walked into stable and changed regions, exact <<<<<<< ours conflict blocks. Adjacent edits must collide, separated ones must merge cleanly, identical insertions must collapse to one copy.
32 — Job-shop scheduler
A deterministic scheduler graded on its event log - with the specification deliberately scattered: the model in TASK.md, tie-breaks and validation in a code comment block, the log grammar defined only by an annotated example file. Assembling the spec is the task.
33 — Scoped DI container
Delegate-factory dependency injection with three lifetimes, cycle errors that spell the full path (Alpha -> Beta -> Alpha), captive-dependency detection through transient chains, and a create/dispose log whose order - dependencies first, reverse on disposal - is asserted exactly.