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

# Create a check from selected source

> Choose repository files or line ranges and explain existing code at a fixed revision.

Create an understanding check for code you want to understand, even when there is no pull request. You need an active workspace membership and access to a connected GitHub repository. The check is for you; assigning it to another member is not supported.

## 1. Choose a repository and branch

Open **Understanding checks** in the [Second Flow console](https://console.secondflow.app/understanding) and select **Create understanding check**.

In **Repository**, choose a repository and branch. Second Flow resolves the branch to a fixed commit. The check will keep that revision even if the branch later advances or is deleted.

## 2. Select source

In **Source**, browse files and preview the code. Select whole files or inclusive line ranges as the code you want to explain. You can use line-number controls; Shift-click extends a range.

Add supporting files when they help explain a dependency or data flow. Supporting files ground the questions, but their inclusion alone does not establish understanding coverage.

Keep the selection focused on a coherent behavior. Changing the repository or branch requires clearing the existing source selection.

## 3. Add context

In **Context**, add an optional focus to guide the questions, such as error handling or an authorization boundary. Choose any available connected knowledge that is permitted for this repository.

[Context Gateway](https://docs.secondflow.app/guides/context-gateway.md) selections and audience approval still apply. Selecting connected knowledge for a check does not grant access to other provider material.

## 4. Review and create

In **Review**, check the repository, fixed revision, selected source, supporting files, and context. Use the section's edit action to change a selection.

Select **Create understanding check**. Wait for the questions to be prepared, then open the check. Read each question and its sources, enter your responses, and select **Complete check**.

Review your result and feedback. After completion, **Continue explanation** requests follow-up questions for the same source selection and revision. Earlier explanations and results stay read-only.

## Selection limits and unavailable source

You can select up to 100 assessed and supporting files combined. Each file must be a readable text file no larger than 256 KiB, and the complete selected files and their paths must fit within 1 MiB. Selecting a short range still requires the full file to fit the limit.

Binary files, excluded paths, unavailable files, and line ranges outside a file cannot be selected. If access is lost or the source cannot be verified, restore access or adjust the selection and create a new check.

If creation is temporarily limited, follow the retry information shown in the console. Your current selection is preserved.

## How these checks affect your repository

Completed explanations can contribute [source understanding coverage](https://docs.secondflow.app/guides/understanding-coverage.md) for the behavior assessed at the selected revision.

A source-selected check does not create a GitHub status or check run and does not affect pull-request eligibility or merge enforcement. Pull-request checks continue to use the repository's [understanding policy](https://docs.secondflow.app/guides/understanding-policy.md).


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