Timed coding drills where the interviewer never solves.
228 problems, with your approach stated before the clock starts. Run checks the examples in a throwaway sandbox. In Java, Submit sweeps generated inputs against a correct implementation on 164 of them. State is local first, with encrypted sync.
Architecture
A drill, end to end
No cron and no polling on the drill path; a one-second interval only redraws on-screen timers.
Drill page → Local storage: every change written here first (event, sync)
Drill page → Sign-in check: sign in; every route checks the session (request, sync)
Sign-in check → Postgres revisions: credential read on every call; session tokens not stored (request, sync)
Drill page → State sync: save 6 s after the last change; a stale write merges (timer, async)
State sync → Postgres revisions: encrypted revisions, last 30 kept (request, sync)
Drill page → Run route: Run or Submit (request, sync)
Run route → Throwaway Micro virtual machine — A small virtual machine started for one job and thrown away after it.: create, run, stop in a finally block (request, sync)
Throwaway Micro virtual machine — A small virtual machine started for one job and thrown away after it. → Runner snapshot: boot from the prebuilt runner image (request, sync)
Run route → Gemini oracle: Submit only: your code and the statement (request, sync)
Drill page → Local Ollama: analysis of logged attempts, on a device that can reach it (request, async)
Submit
The bound is worked out from the statement ahead of time and never sees your code. The oracle is written per Submit.
Submit → Check the signature: Java source and signature (request, sync)
Check the signature → Write the oracle: code and statement, sent only after the signature passes (request, sync)
Write the oracle → Sweep the inputs: oracle appended after your code, never returned (request, sync)
Sweep the inputs → Smallest failing case: first disagreement, shrunk (response, sync)
Problem file → Submit: stored bound, worked out ahead of time, shown beside it (event, sync)
Smallest failing case → Submit: verdict, smallest case, your code's complexity (response, sync)
Which line? → Local Ollama: the failing input goes to a local model (request, async)
Smallest failing case → Which line?: hand off the failing case (event, sync)
Wiremocks
A mock-up of a screen — Here, a static picture of a screen, drawn to show layout and flow, not the working app. — a static picture, not the real app
The console after Run and Submit
A drawing of the console on a made-up problem; Run checks the examples, Submit sweeps generated inputs.
After Run: Testcases and Output
Pair sum: return the indices of two numbers that add to a target.
Case 1Pass
nums = [4, 1, 8, 5], target = 9
Expected [0, 3], got [0, 3]
Case 2Fail
nums = [5, 5], target = 10
Expected [0, 1], got [1, 1]
Case 3unchecked
nums = [1, 5, 9], target = 14
No expected output, so nothing was compared
Each run is capped at 12 seconds.
After Submit: the sweep
Disagrees with the reference on a generated input
Smallest failing case
nums = [4, 9, 4], target = 8
Yours returned [0, 0]; the reference returned [0, 2].
Your solution: O(n²) · Achievable: O(n)
Which line?
Which line? hands the failing input to a local model.
Running cost
Resource
Figure
Status
Source
Sandbox Central processing unit — The main chip that executes a computer's instructions., Run
~2.1–2.7 secondsper run
Measured
build log, line 1019
Read on 2026-10-17
Sandbox Central processing unit — The main chip that executes a computer's instructions., Submit sweep
~9–11 secondsper sweep
Measured
build log, line 1019
Read on 2026-10-17
Sandboxes created
at most 1per Run or Submit
Set in the project's code
run route, lines 203-206 and 327-332 (a request refused before create costs nothing)
Read on 2026-10-17
One production Run, end to end
5,331 msone run
Measured
build log, line 6383 (2026-10-15; 1,547 ms of it boot)
Read on 2026-10-17
Conflicts with readme, lines 443-444 and 477 (boot under 300 ms, read on 2026-10-17): The build log is newer and measured, so it governs the row.
Runner snapshot
833 Megabyte — Megabyte, a million bytes.no expiry
Measured
build log, line 6378 (2026-10-15)
Read on 2026-10-17
Conflicts with readme, line 461 (about 0.94 Gigabyte — A billion bytes of data; storage is priced per gigabyte per month. with a 14-day expiry, read on 2026-10-17): The build log is newer and measured, so it governs the row.
Vercel Sandbox plan
—
Not verified
owner's metered-resource table (Vercel Sandbox, plan tier marked verify, names this project)
Read on 2026-10-17
Gemini requests
20per day per model
Measured
owner's metered-resource table (Gemini free tier row); build log, lines 1530-1531 (seen in 429 responses; the provider does not publish it, build log line 1135)
Read on 2026-10-17
Gemini requests per Submit
1 (0 with your own oracle class)
Set in the project's code
problem page, lines 661, 2526, 2538 and 2543 (no bound call when the file has one); oracle module, lines 356-360 (no retry)
Read on 2026-10-17
Conflicts with build log, line 1130 (2 if the first is rejected and retried, read on 2026-10-17): The log is older and the code has no retry now, so the code governs the row.
Submits a day at the cap
20per day
Derived
derived (see inputs)
Inputs: 20 requests a day (measured) ÷ 1 per Submit (configured) = 20
Read on 2026-10-17
Gemini price
$0.00
Published price
build log, lines 1128-1129 (quoting the free tier's price)
Read on 2026-10-17
Edge requests per Run or Submit
1
Set in the project's code
build log, lines 1015-1022 (one route call per click; a planning table)
Read on 2026-10-17
Vercel edge requests, plan
One million — Shorthand in prices and limits, as in $1 per 1M tokens.per month, shared by about 10 projects
Published price
owner's metered-resource table (Vercel Requests Vercel counts at its edge — Every request Vercel serves (a page, a script, an image) counts as one.)
Read on 2026-10-17
Conflicts with readme, lines 489-490 (15 projects, read on 2026-10-17): The owner's row is newer, so it governs the row.
Neon compute
$0.106per Compute unit — The unit a serverless database bills its processing time in; one unit-hour is one unit running for one hour.-hour
Published price
owner's metered-resource table (Neon Postgres; the org bills on Launch from 2026-09-29)
Read on 2026-10-17
Conflicts with readme, line 508 (free tier, read on 2026-10-17): The owner's row is newer, so it governs the row.
Attempt analysis runs on a local Ollama, no hosted Application Programming Interface — A defined way for one program to request data or actions from another.. Storage outside the drill is not counted.
Design decisions
The interviewer never solvesThe hint pane stays sealed until you confirm your approach; naming an approach is on the interviewer's never list.
One throwaway Micro virtual machine — A small virtual machine started for one job and thrown away after it. per runEach run boots from a prebuilt snapshot, so a runaway loop dies with its Micro virtual machine — A small virtual machine started for one job and thrown away after it.. Without the flag that discards a stopped session, each stop wrote a ~900 Megabyte — Megabyte, a million bytes. snapshot and one day filled storage.
Correctness is a sweep, never a modelA differential sweep compares your code with a correct implementation on generated inputs. A model once graded a correct solution as failing.
The bound never sees your codeThe bound is worked out from the statement alone, so it never sees your code and cannot echo a slow solution. Every problem file stores one; 153 are stamped as written by a local model.
Local-first state, encrypted syncChanges land in the browser first, then sync as encrypted revisions. Models run locally on Ollama; on the live path the one exception is the free-tier Gemini oracle.
Open questions
Vercel Sandbox plan: the readme (lines 79-85) infers Hobby from the 12-function cap; the owner's row says verify
Sandbox usage: monthly Active Central processing unit — The main chip that executes a computer's instructions. and Gigabyte — A billion bytes of data; storage is priced per gigabyte per month.-hours are not measured
Neon: the drill's share of Compute unit — The unit a serverless database bills its processing time in; one unit-hour is one unit running for one hour.-hours is not measured
Edge requests: the usage Application Programming Interface — A defined way for one program to request data or actions from another. is Pro-only, so there is no month-to-date count
Gemini billing: whether the key's project has a billing account is not recorded