A handful of small tools that pay for themselves once

This page collects the only five custody tools I think are worth the time. They do not require a backend, no account creation, no data leaves your browser. Each is one HTML file you can save and run offline.

What is here

  • Mnemonic format checker. Paste in a 12 or 24 word phrase. The page checks: are all words in the BIP-39 wordlist, is the checksum valid, what is the corresponding hexadecimal entropy. Runs entirely in your browser — the words never leave the page. Useful for verifying that a seed you copied or transcribed is internally consistent before you commit to using it.
  • Custody risk calculator. Answer eight questions about your setup — device type, backup location, family handoff plan, value range. The calculator returns a numeric risk score and a short list of the three highest-impact changes you could make this week.
  • Wallet picker. Answer four questions — how much you hold, how often you move it, how comfortable you are with the technical side, and what you care about most — and it points you to a setup that fits: exchange custody, a hot wallet, a hardware cold wallet, or a hot-cold combination. A starting point, not a verdict. Runs entirely in your browser.
  • Wallet security checklist. Tick off the security steps for storing and sending, one by one: seed phrase backup, account 2FA, double-checking the address before a transfer, revoking stale approvals on a schedule. Comes with a progress bar so you can work through it item by item. Runs entirely in your browser and collects nothing.
  • The 30-item self-check. See the checklist page. Thirty questions about your security setup, with priorities. Print, fill in, revisit quarterly.

Why these and not others

Most "crypto security tools" online are either marketing for a hardware wallet brand, or a thin wrapper around BIP-39 reference code with telemetry built in. The four above are deliberately minimal — they solve specific narrow problems without adding new attack surface. Save the HTML files locally if you want to run them on an air-gapped machine.

What is not here, deliberately

Address generators. Brain-wallet helpers. "Strong password" generators. Anything that creates new key material in a web browser. These are all genuinely useful concepts in the right context — but the right context is rarely "in a web page on the internet." Tools that generate or accept secret material should run offline, on a device you control, with no network. If a future tool here ever moves in that direction, the page will say so prominently and link to instructions for running it air-gapped.