> ## Documentation Index
> Fetch the complete documentation index at: https://docs.blockscout.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Indexer Architecture Overview

> Learn how the indexing architecture works in Blockscout

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## Presentation Highlights

The following presentation describes the past, present and future iterations of Blockscout along with details about how block imports work both synchronously and asynchronously, and a description of the regular and on-demand fetchers.

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  1MB pdf
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## Blockscout indexers

See the pdf ⬆️ for more details about the Blockscout indexer. The indexing architecture includes all of the following indexers and fetchers

### Primary Indexers

Both indexers utilize synchronous and asynchronous operations.

* Realtime: Imports new block data from the head of the chain.
* Catchup: Imports data down the chain (starting from the head and moving backwards towards the genesis block)

### Secondary fetchers

### Regular

* Internal transactions
* Pending transactions
* Dropped/Replaced transactions
* Contract bytecodes
* Block rewards
* Token catalog
* Token/coin balances
* NFT instances
* Uncles

### On Demand

* Coin/token balances update
* Contract bytecodes fetch/re-check
* Contract source codes lookup
* NFT instance metadata re-fetch
* Token total supply

### Off-chain integrations

* Coin / token price, market cap, tvl sources: CMC, Coingecko, Cryptorank, Defillama
* Smart contract verification: ETH bytecode DB, Sourcify
* Data enrichment: ENS names, public tags, AI interpreters (own, Noves Fi), sc security scanners (Solidityscan), assets portfolio (Zerion)
* Chain initialization data import: pre-mined coins, precompiled smart-contracts

### Chain-specific fetchers

* There are more than a dozen of chain-specific data fetchers to account for chain differences including arbitrum, optimism, polygon zkevm, zksync etc.

### Temporary fetchers

* Used once to resolve possible data inconsistencies.