> ## 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.

# Umbrella Project Organization

> How the BlockScout project is organized

BlockScout is an Elixir [umbrella project](https://elixir-lang.org/getting-started/mix-otp/dependencies-and-umbrella-projects.html). Each directory under `apps/` is a separate [Mix](https://hexdocs.pm/mix/Mix.html) project and [OTP application](https://hexdocs.pm/elixir/Application.html), but the projects can use each other as a dependency in their `mix.exs`.

Each OTP application has a restricted domain.

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|                         |                     |                   |                                                                                                                                                                                                                                                                                                                                                                          |
| ----------------------- | ------------------- | ----------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Directory               | OTP Application     | Namespace         | Purpose                                                                                                                                                                                                                                                                                                                                                                  |
| `apps/ethereum_jsonrpc` | `:ethereum_jsonrpc` | `EthereumJSONRPC` | Ethereum JSONRPC client. It is allowed to know `Explorer`'s param format, but it cannot directly depend on `:explorer`                                                                                                                                                                                                                                                   |
| `apps/explorer`         | `:explorer`         | `Explorer`        | Storage for the indexed chain. Can read and write to the backing storage. MUST be able to boot in a read-only mode when run independently from `:indexer`, so cannot depend on `:indexer` as that would start `:indexer` indexing.                                                                                                                                       |
| `apps/block_scout_web`  | `:block_scout_web`  | `BlockScoutWeb`   | Phoenix interface to `:explorer`. The minimum interface to allow web access should go in `:block_scout_web`. Any business rules or interface not tied directly to `Phoenix` or `Plug` should go in `:explorer`. MUST be able to boot in a read-only mode when run independently from `:indexer`, so cannot depend on `:indexer` as that would start `:indexer` indexing. |
| `apps/indexer`          | `:indexer`          | `Indexer`         | Uses `:ethereum_jsonrpc` to index chain and batch import data into `:explorer`. Any process, `Task`, or `GenServer` that automatically reads from the chain and writes to `:explorer` should be in `:indexer`. This restricts automatic writes to `:indexer` and read-only mode can be achieved by not running `:indexer`.                                               |