UMA Optimistic Oracle

Best for Arbitrary onchain assertions settled by bonds and disputes

Chains

Ethereum Base Arbitrum Polygon Avalanche

Price

No usage fee published; asserters post a bond at least equal to the final fee per collateral type (e.g. 250 USDC)

License

AGPL-3.0

UMA's Optimistic Oracle is not a price feed: it records any verifiable statement or data onchain, which is accepted as true unless disputed during a challenge window, with disputes arbitrated by UMA token holders through the DVM. Developers integrate OOv2 (request and propose) or OOv3 (assertTruth), post a bond at least the final fee, and the docs recommend a challenge window of at least two hours. A successful OOv3 disputer receives half the proposer bond; the protocol repo is AGPL-3.0 and actively updated.

Catch Not a price feed; answers wait out a challenge window (2 hours recommended) and need bonds