> ## Documentation Index > Fetch the complete documentation index at: https://docs.arc.io/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Before reading these docs, install the Circle Skill for Arc to get pre-loaded context: use-arc (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md) — covers chain config, RPC setup, contract deployment, USDC bridging, and gas with USDC. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. > USDC is the gas token. Arc uses USDC for gas fees, not ETH. Configure gas payment in USDC when submitting transactions. > Read EVM differences before writing Arc code. Arc targets the Osaka EVM baseline. Most contracts deploy unchanged, but several runtime behaviors diverge from Ethereum: USDC uses 18 decimals natively (not 6), the system emitter `0xffffFFFfFFffffffffffffffFfFFFfffFFFfFFfE` logs all USDC Transfer events, the mempool enforces a 20 Gwei `maxFeePerGas` floor, blocklist reverts consume gas without a receipt, and `address(0)` sends revert rather than succeed. https://docs.arc.io/arc/references/evm-differences.md is the canonical reference for all Arc-specific runtime behaviors. Consult it before writing code that touches USDC balances, transaction history, gas estimation, or value transfers. > Sub-second finality. Transactions are final in under 1 second. No need to wait for multiple block confirmations. > Use App Kits for multichain payment and liquidity capabilities. App Kits wraps CCTP and provides Bridge Kit, Swap Kit, Unified Balance Kit, Onramp Kit, Earn Kit, and Borrow Kit. Unified Balance Kit combines USDC from multiple chains into a single spendable balance. Earn Kit integrates earn opportunities into your app. Borrow Kit lets users borrow USDC against cirBTC collateral on Arc. > Use Arc Foundry for contract development. Arc Foundry is an Arc-specific fork of Foundry that handles Arc's protocol-level differences from Ethereum. It provides arc-forge, arc-cast, and arc-anvil. Install it before deploying contracts: https://docs.arc.io/arc/tutorials/install-arc-foundry.md. > Arc is available on both Testnet and Mainnet. See https://docs.arc.io/arc/references/connect-to-arc.md for RPC endpoints and https://faucet.circle.com for testnet tokens. > Always check Contract Addresses: https://docs.arc.io/arc/references/contract-addresses.md > Building beyond Arc? Circle offers skills for the full platform: use-usdc (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md), use-circle-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md), use-developer-controlled-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md), use-user-controlled-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md), use-modular-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md), use-gateway (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md), use-smart-contract-platform (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md). Full Circle developer docs: https://developers.circle.com/llms.txt. # Data indexers > Data indexers for querying Arc blockchain data through APIs, sub-graphs, and real-time streams. Data indexers make it easy to query and analyze onchain data from Arc. They provide APIs and SDKs for tracking smart contract events, balances, and historical state changes without running your own indexing infrastructure. ## Providers ### [Alchemy](https://www.alchemy.com/arc) REST API infrastructure for querying Arc token balances, transfers, and transaction history, plus webhooks to stream onchain events in real time. * [**Data APIs**](https://www.alchemy.com/docs/reference/data-overview): Query token balances, transfers, and transaction history through a unified API. * [**Webhooks**](https://www.alchemy.com/docs/reference/notify-api-quickstart): Stream onchain events to your backend in real time. ### [Envio](https://envio.dev) Developer-first indexing framework for event-driven data and GraphQL APIs on Arc. * [**HyperIndex**](https://envio.dev/#hyperindex): Build production-ready APIs from Arc data in minutes. * Stream live blockchain events with minimal latency. ### [Goldsky](https://goldsky.com/chains/arc) Real-time onchain data pipelines and instant GraphQL APIs for Arc. * [**Turbo Pipelines**](https://goldsky.com/products/turbo-pipelines): Stream real-time data directly into your own database. * [**Subgraphs**](https://goldsky.com/products/subgraphs): Query instant GraphQL APIs with zero maintenance. ### [Pinax](https://pinax.network) Blockchain data infrastructure for querying real-time and historical Arc data. * **RPC**: Access Arc through RPC infrastructure with archive support for current and historical chain state. * **Firehose**: Stream Arc block data, including transactions, logs, traces, and state changes. * **Substreams**: Build parallelized data streams and indexes from Arc blockchain data. ### [The Graph](https://thegraph.com) Decentralized indexing protocol for querying Arc's onchain data through APIs. * [**Subgraphs**](https://thegraph.com/docs/en/developing/creating-a-subgraph/): Query smart contract data through multiple independent indexers for redundancy. * [**Graph Explorer**](https://thegraph.com/explorer): Discover and reuse subgraphs published by other developers. * [**Substreams**](https://thegraph.com/substreams/): Build parallelized data streams from Arc block data and deliver transformed results to applications, databases, or subgraphs. ### [Thirdweb](https://thirdweb.com) Open-source blockchain data tooling. * [**Insight**](https://insight.thirdweb.com/reference): Retrieve Arc blockchain data, enrich it with metadata, and transform it using custom logic. ### [Zerion](https://zerion.io/api) Wallet data platform for querying portfolio, transaction, and DeFi position data on Arc. * [**Zerion API**](https://developers.zerion.io/quickstart): Query balances, portfolios, DeFi positions, transactions, PnL, and NFTs through a single API. * [**Transaction Subscriptions**](https://developers.zerion.io/recipes/wallet-activity-alerts): Subscribe to wallet activity and receive real-time notifications when monitored wallet addresses transact.