Sub-Issues and Parent Issues

Sub-issues let you break down work into hierarchical tasks. Each parent issue can have up to 100 sub-issues, nested up to 8 levels deep. Sub-issues can span repositories within the same owner.

Recommended Workflow

The simplest way to create a sub-issue is two steps: create the issue, then link it.

# Step 1: Create the issue and capture its numeric ID
ISSUE_ID=$(gh api repos/{owner}/{repo}/issues \
  -X POST \
  -f title="Sub-task title" \
  -f body="Description" \
  --jq '.id')

# Step 2: Link it as a sub-issue of the parent
# IMPORTANT: sub_issue_id must be an integer. Use --input (not -f) to send JSON.
echo "{\"sub_issue_id\": $ISSUE_ID}" | gh api repos/{owner}/{repo}/issues/{parent_number}/sub_issues -X POST --input -

Why --input instead of -f? The gh api -f flag sends all values as strings, but the API requires sub_issue_id as an integer. Using -f sub_issue_id=12345 will return a 422 error.

Alternatively, use GraphQL createIssue with parentIssueId to do it in one step (see GraphQL section below).

Using MCP tools

List sub-issues: Call mcp__github__issue_read with method: "get_sub_issues", owner, repo, and issue_number.

Create an issue as a sub-issue: There is no MCP tool for creating sub-issues directly. Use the workflow above or GraphQL.

Using REST API

List sub-issues:

gh api repos/{owner}/{repo}/issues/{issue_number}/sub_issues

Get parent issue:

gh api repos/{owner}/{repo}/issues/{issue_number}/parent

Add an existing issue as a sub-issue:

# sub_issue_id is the numeric issue ID (not the issue number)
# Get it from the .id field when creating or fetching an issue
echo '{"sub_issue_id": 12345}' | gh api repos/{owner}/{repo}/issues/{parent_number}/sub_issues -X POST --input -

To move a sub-issue that already has a parent, add "replace_parent": true to the JSON body.

Remove a sub-issue:

echo '{"sub_issue_id": 12345}' | gh api repos/{owner}/{repo}/issues/{parent_number}/sub_issue -X DELETE --input -

Reprioritize a sub-issue:

echo '{"sub_issue_id": 6, "after_id": 5}' | gh api repos/{owner}/{repo}/issues/{parent_number}/sub_issues/priority -X PATCH --input -

Use after_id or before_id to position the sub-issue relative to another.

Using GraphQL

Read parent and sub-issues:

{
  repository(owner: "OWNER", name: "REPO") {
    issue(number: 123) {
      parent { number title }
      subIssues(first: 50) {
        nodes { number title state }
      }
      subIssuesSummary { total completed percentCompleted }
    }
  }
}

Add a sub-issue:

mutation {
  addSubIssue(input: {
    issueId: "PARENT_NODE_ID"
    subIssueId: "CHILD_NODE_ID"
  }) {
    issue { id }
    subIssue { id number title }
  }
}

You can also use subIssueUrl instead of subIssueId (pass the issue's HTML URL). Add replaceParent: true to move a sub-issue from another parent.

Create an issue directly as a sub-issue:

mutation {
  createIssue(input: {
    repositoryId: "REPO_NODE_ID"
    title: "Implement login validation"
    parentIssueId: "PARENT_NODE_ID"
  }) {
    issue { id number }
  }
}