# Sidecar

Chains leverage Javelin by running a sidecar. The sidecar runs alongside the chains validators/sequencers and allows them to opt into a shared auction that runs across all the chains in the network to help facilitate cross-chain composability. 

Chains register ahead of time to this shared auction and this allows Javelin builders to bid on a shared slot across chains. These shared slots are done in epochs that last 12 seconds. A builder bids for the right to build across all chains in the Composium for a given epoch. 

Blocks are built and sent to the chain in time with the chain’s blocktime. Builders switch every epoch. Chains benefit by unlocking cross-chain composability with Javelin while being able to maintain flexibility in their stack and allowing them to have their own block time without giving up any revenue.

Chains benefit by unlocking cross-chain composability with Javelin while being able to maintain flexibility in their stack and allowing them to have their own block time without giving up any revenue.

<figure><img src="/files/kzafBPSx5mUxRsOuR9Zp" alt=""><figcaption></figcaption></figure>


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://nodekit.gitbook.io/nodekit-documentation/architecture/sidecar.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.