A Filled PDF Is a Claim. A Run Is a Receipt.

A filled PDF is a claim.
A run is a receipt.

A PDF says trust me. A run says check me. Below is the same small task done twice: once the way most forms still work, and once as a run you can hand to someone and they can check it themselves, in seconds, without asking you anything.

This takes about a minute. Type in your own numbers if you want. Nothing you enter leaves your browser.

Sixty seconds Interactive demo Zero PII

Three things happen, in order

You pick the situation you're in and type in the numbers you already have. That is the entire job. Nothing else is required of you.

It computes the answer, seals the result, and hands you a receipt. The seal is a fingerprint of the numbers and the answer together, so changing either one changes the fingerprint.

You send that receipt to whoever has to trust the answer. An auditor, a counterparty, your boss. They check the fingerprint themselves instead of taking your word for it.

The same fee calculation, done both ways

Here is a small, real example: working out the total cost of sending an invoice payment across a border, once you add the currency spread and the correspondent bank's fee. Change the numbers if you like, then run both sides.

All inputs are processed locally in your browser. No data is transmitted. Do not enter real personal data, use synthetic or anonymised inputs only.

Invoice amount ($)

FX spread (bps)

Correspondent fee ($)

The PDF world

$0.00

This is what a filled-in form or a spreadsheet would show you. It looks exactly as confident as the other side.

There is nothing here to check. If someone else needs to know this number is right, they have to redo the math themselves, from scratch, and trust that they did it the same way you did.

The verified run

$0.00

Same numbers, same arithmetic. The difference is what happens after it computes.

The situation picker is boring on purpose

A form like the one above only lets you pick from a fixed list of situations and fill in a fixed set of numbers. That reads as old-fashioned next to a chat box you can type anything into. It is old-fashioned, and that is the point.

A free-text box that can answer anything can also answer differently tomorrow, and nobody downstream can check that against anything. A dropdown works the same way a legal form works: numbered fields instead of a blank page. Constrained input is what makes the output something a second person can check without redoing your work.

"It looks like a boring form on purpose. Boring is what auditors accept."

The same structured fields also let a software agent fill this in over MCP, the protocol AI assistants use to call tools directly, because a form a machine can fill in is a form a machine can check too.

Want to chain a few of these together?

Most real questions take more than one step. The Workbench lets you connect several runs so the receipt from one feeds the numbers into the next.

How this works, for the technically curious

The seal is a SHA-256 hash computed over the run's inputs and outputs together, using the same canonicalization (RFC 8785 / JCS) as every kernel on this site: see chaingraph/kernels/_hash.mjs, and a full production version of this exact fee calculation at art-367, Compute Cross-Border Fees.

Checking a receipt means recomputing that hash from the numbers you were given and confirming it matches the one you were handed. This page does that for real: "Check this" on the right recomputes the hash in your browser and compares it, live, to the sealed value. "Change one digit" edits the displayed total after sealing, without touching the seal, so the mismatch you see next is genuine, not staged.

In the full standard this artifact is called an OpenChainGraph run and the hash is the execution_hash. A chain of these proves a computation happened deterministically and can be reproduced by anyone who receives it.