A speed camera for methane, written into the gas contract between an EU gas importer and its supplier.

Satellites confirm a leak → the seller's bond pays the buyer. No new leak on later passes → the seller earns money back in steps, up to the rebate, from a sponsor's pool (for example its lender's). No one runs the payout: once enough independent witnesses sign the same sighting and the appeal window passes, the contract pays the buyer from the bond. The seller can appeal — then the witnesses must confirm it again — but cannot delete the sighting or hold the money.

Watch the story on the map The leak, the witnesses and the payout, chapter by chapter on a 3D map. Step through the penalty case Become a witness

A judge's 10-minute path: read the clause live from Sepolia, break a signature (tamper A–C), open the reverted transactions on the explorer, sign with your own key. The full path, step by step →

Amounts are representative test values; a production clause sets them in euros in the parties' policy.

In this demo one person runs every role; in production each witness is a separate organisation with its own keys.

Red: the seller's bond pays the buyer when a leak is confirmed. Green: a sponsor (the seller's lender, as a sustainability-linked margin step, or the buyer) pays the seller back from its pool, in steps, for clean passes; a new confirmed leak cancels only the unpaid steps.

Penalty and earn-back, step by step

Who pays whom, and when

Four parties and three paths. The sightings come from Carbon Mapper and UNEP MARS; the money moves in real transactions on Ethereum Sepolia and in a recorded local run.

seen→confirmed→paid
clean passes→earn-back in steps
new leak→the earn-back stops

The 60-second proof

Try to cheat it

Three edits a seller might try. Every check runs in your browser (RFC 8785 + SHA-256, EIP-712 ECDSA, ML-DSA-44); a rebate and an earn-back fail the same way.

1The seller edits the signed leak rate
2Both witnesses' signatures fail
3The contract refuses; the bond does not move

See the signature checks ↓

A · Edit the rate of the signed sighting

The record two witnesses signed for the plume the clause settles. Change the rate and watch both signatures fail.

emissionKgH

Committed evidenceHash (what both witnesses signed)

Recomputed in your browser from the signed record shown here (RFC 8785 + SHA-256)

B · Delete a sighting from the list

The seller hides a sighting from the provider's list; the witness's re-fetch receipt no longer matches, so it refuses to sign.

Witness's re-fetch receipt (hash of the list the provider serves)

Recomputed in your browser from the list shown here (RFC 8785 + SHA-256)

C · Make a cloudy scene look clear (the earn-back side) MOCK data

The seller edits a scene's cloud fields to earn money back; the signed sceneHash changes and both witnesses' signatures fail.

cloudCoverPct cloudCoverPctAssessed notCloudy

Committed sceneHash (inside the signed clean pass)

Recomputed in your browser from the scene record shown here (RFC 8785 + SHA-256)

Your own key

Become a witness

Sign the TKM_S_276 sighting with your own browser test wallet in the public judge sandbox on Ethereum Sepolia.

How it works

Your key joins the registry as witness organisation OBS_JUDGE, your signature is one of the two the clause needs, and the contract — not this page — decides. The page asks your wallet to sign and to send; it never sees your key.

(needs MetaMask + Sepolia test ETH)

a throwaway key made in this tab signs the same record; nothing is sent

No browser wallet? The same flow runs from a terminal: make judge-local (a local chain, no test ETH needed) or make judge-attest then make judge-propose with JUDGE_PK set (Ethereum Sepolia).

The words on this page and in the contract

The page uses everyday words; the specification, the code and the ABI keep the exact terms: confirmed leak = episode · clean pass = qualified clean pass · earn-back step = installment · appeal window = challenge window · witness = observer organisation · clause = covenant.

A judge's 10-minute path

In order. Each step says what you see on this page and where to check it without trusting this page: the public explorer, a file in the repository, or a command.

Why a clean pass counts

What a witness does: Fetch → Validate → Seal → Sign → Re-check

Checked in your browser

Nothing here trusts our server: hashes, signatures and chain reads run on this page.

The clause, read live from Ethereum Sepolia

The seller posted a bond; sightings signed by k witness organisations, each designed to hold its own keys, rebate the buyer after an appeal window.

Confirmed leaks and rebates

Every rejection below is a real transaction that failed on chain (receipt status 0) with the bond unchanged.

Waiting windows: skipped in the replay, real on Sepolia

On a local chain the demo moves the clock forward only, over each window, and says so; on Ethereum Sepolia nothing is skipped.

Recorded local run [SIM clock]

Ethereum Sepolia: waited out in real time

File it: IEA Annex D, the seller's Annex C, the credit note

Official template labels only; what public data cannot support says so. Protocol fields live under x-methaneclause and are never presented as official.

Download JSON Download CSV

EU evidence mapping (Regulation (EU) 2024/1787) and the MARS vocabulary — evidence a filer may cite, never a statement of compliance

The seller's side: IEA Annex C, recorded on chain by hash

Download JSON Download CSV

Where crypto payments are not lawful: the verdict as a credit note [SIM]

Download register JSON Download register CSV

How long verification takes: by hand vs with the tool

Manual protocol

Tool

0.000 s

Full record per source: leak → clean passes → new leak

The exact terms: a confirmed leak is an episode, a clean pass a qualified clean pass, an earn-back step an installment. Each panel shows the Carbon Mapper CH₄ scene it rests on (Data by Carbon Mapper®), the MARS label, and what moved on chain.

Sources under the clause

Verify on the explorer: every Sepolia transaction this page relies on

Contracts and parties, from the deployment record

Limits

Stake, not abatement. A rebate follows an attested plume; an earn-back follows passes that saw none. Annualised rates are a stake and only the stake's low bound is quoted. Observed, not abated.
Non-detection is not repair. A clean pass never cancels a rebate or counts as repair; it bounds how often a source emits above the instrument's floor, not its rate. It can release a refund that never exceeds the rebate that episode cost, is frozen while a new detection is under review, and is cancelled by any later attested detection at that source; installments already released are not clawed back, and the final share waits for the cure term.
Floor blindness, both ways. A source emitting just below the instrument's detection floor is invisible to the rebate and to the refund alike.
One provider's scene catalogue, and tasking. Qualified clean passes come from Carbon Mapper's catalogue; k-of-n witnesses guard against one witness's error or key, not against an error of the provider, and UNEP MARS is used against the negative (a MARS plume within the window refuses the pass). A seller can request Carbon Mapper passes during a planned shutdown, so the final tranche needs two instruments, the MARS corroboration and the cure term.
What the chain sees. It verifies that k organisations signed the same named fields; the cloud value itself is Carbon Mapper's. Witnesses attest what they received, from whom and when — not what the satellite saw; Carbon Mapper and UNEP do not sign their data.
Records only grow. Re-quantification never edits a confirmed episode (a later correction is a new record). Scenes published after the covenant's end plus the publication lag and the clean-pass window cannot be attested. A relapse is read from the core's latest episode at the source, so the sponsor watches and reports relapses.
Prototype keys and clocks. In this prototype the witness organisations are run by one person [SIM]; a judge's own wallet is designed to be the one signer we do not control. Seller, buyer and sponsor are [SIM]. The DZA replay runs on a [SIM clock]: every DZA date was public before this covenant was written, so the replay proves the mechanism, not the absence of foreknowledge. On Sepolia createdAt is real and later than the plumes and passes it settles (starts backdated); the chain shows the plume was public first. The satellites' sky positions and paths are drawn; their pass dates and images are real.
Post-quantum boundary. The on-chain check is secp256k1 ECDSA; ML-DSA-44 protects bundle authenticity off-chain. We do not claim a quantum-safe chain. Tamper-evident, not tamper-proof.
Not legal compliance, not a payment instrument. The exports are evidence for a regulator's form, never a finding of compliance. Money here is testnet ETH; where crypto payments are not lawful the verdict settles as a credit note.
Data licence. Carbon Mapper data is non-commercial; production needs a licence held by the witnesses.