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Prep that checks out.

Checksum is a free-forever study site where every question is checked against the official documentation, links to the exact lines it came from, and is approved by a person before you see it.

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  • No paywall
  • No card, ever

Why we built Checksum

When we went looking for certification study guides, we kept finding books on Amazon and other big bookstores that read like unchecked AI output: confident, generic, and sometimes wrong about how a service actually works.

Amazon’s own publishing rules now have a section on AI content. Publishers must tell Amazon when a book’s text is AI-generated, and “You are not required to disclose AI-assisted content.”

So we built the opposite. Every answer on Checksum links to the exact line of official documentation it came from, and a person approves it before you see it.

Before you buy any study guide, ask one question: can you check where each claim comes from?

Read the full note

How every question is checked

Nothing reaches you until it passes every step. A single failure anywhere blocks it.

  1. Written only from official documentation

    Each question and lesson is drafted from a saved copy of an AWS, Microsoft, Python or MDN documentation page. Every fact in it carries the exact sentence it came from.

  2. Checked by code, two AI reviewers and the live page

    Code confirms that every quote appears word for word in its source. Two separate AI models then check each claim against its quote and answer each question without seeing the key. A last pass rereads the vendor’s live page.

  3. Approved by a person

    A person reads every item beside its sources and approves it before you see it. Tap any footnote and you can read the same quote yourself.

See the full method and our sources

Pick your exam

Grouped by provider, with the tracks we plan next. Each one follows the official exam outline, domain by domain. Everything is free, and no card is ever asked for.

Amazon Web Services

0 tracks · 3 planned

Microsoft

0 tracks · 2 planned

Coding interviews

Python and JavaScript · 8 of 16 patterns built

Patterns and problems, run in your browser

40 original problems so far, each with tests and reference solutions in both languages. The problems are waiting for review before they open.

  1. 01Arrays and hashing, 5 problems built
  2. 02Two pointers, 5 problems built
  3. 03Sliding window, 5 problems built
  4. 04Stack, 5 problems built
  5. 05Binary search, 5 problems built
  6. 06Linked lists, 5 problems built
  7. 07Trees (DFS and BFS), 5 problems built
  8. 08Tries, 5 problems built
  9. 09Heaps and priority queues, planned
  10. 10Backtracking, planned
  11. 11Graphs (BFS, DFS, topological sort), planned
  12. 12Union-find, planned
  13. 131-D dynamic programming, planned
  14. 142-D dynamic programming, planned
  15. 15Greedy and intervals, planned
  16. 16Bit manipulation, planned

Study the official path too

Checksum is built to work alongside the vendors’ own prep, not to replace it. Every track page links its official path as well.

SAA-C03

AWS publishes its own prep for this exam. Use it alongside Checksum: the official path teaches the material, and Checksum helps you check that you really know it.

AI-901

Microsoft publishes two learning paths for AI-901 on Microsoft Learn. Work through them alongside Checksum.

Save your progress

Sign in with a code we email you. There is no password to remember, and your answers, reviews and readiness follow you to any device. Checksum stays free either way.

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