Three small tools that pay for themselves once
This page collects the only three 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.
- 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 three 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.