How to Attach Line-Specific Review Comments to Pull Requests

This guide explains how to add line-specific review comments to pull requests using the GitHub CLI (gh) API or mcp__github_inline_comment__create_inline_comment if it not available, similar to how the GitHub UI allows commenting on specific lines of code.

Preferred Approach: Using MCP GitHub Tools

If available, use the mcp__github_inline_comment__create_inline_comment MCP tool for posting line-specific inline comments on pull requests. This approach provides better integration with GitHub's UI and is the recommended method.

Fallback: If the MCP tool is not available, use the GitHub CLI (gh) API methods described below:

• For single comments: Use the /comments endpoint (see Adding a Single Line-Specific Comment)
• For multiple comments: Use the /reviews endpoint (see Adding Multiple Line-Specific Comments Together)

Overview

While gh pr review provides basic review functionality (approve, request changes, general comments), it does not support line-specific comments directly. To add comments on specific lines of code, you must use the lower-level gh api command to call GitHub's REST API directly.

Prerequisites

1. GitHub CLI installed and authenticated:

   gh auth status

1. Access to the repository and pull request you want to review

Understanding GitHub's Review Comment System

GitHub has two types of PR comments:

1. Issue Comments - General comments on the PR conversation
2. Review Comments - Line-specific comments on code changes

Review comments can be added in two ways:

• Single comment - Using the /pulls/{pr}/comments endpoint
• Review with multiple comments - Using the /pulls/{pr}/reviews endpoint

Adding a Single Line-Specific Comment

Basic Syntax

gh api repos/{owner}/{repo}/pulls/{pr_number}/comments \
  -f body='Your comment text here' \
  -f commit_id='<commit-sha>' \
  -f path='path/to/file.js' \
  -F line=42 \
  -f side='RIGHT'

Parameters Explained

Parameter Flags

• -f (--field) - For string values
• -F (--field) - For integer values (note the capital F)

Complete Example

# First, get the latest commit SHA for the PR
gh api repos/NeoLabHQ/learning-platform-app/pulls/4 --jq '.head.sha'

# Then add your comment
gh api repos/NeoLabHQ/learning-platform-app/pulls/4/comments \
  -f body='Consider adding error handling here. Should we confirm the lesson was successfully marked as completed before navigating away?' \
  -f commit_id='e152d0dd6cf498467eadbeb638bf05abe11c64d4' \
  -f path='src/components/LessonNavigationButtons.tsx' \
  -F line=26 \
  -f side='RIGHT'

Understanding Line Numbers

The line parameter refers to the position in the diff, not the absolute line number in the file:

• For new files: Line numbers match the file's line numbers
• For modified files: Use the line number as it appears in the "Files changed" tab
• For multi-line comments: Use start_line and line to specify the range

Response

On success, returns a JSON object with comment details:

{
  "id": 2532291222,
  "pull_request_review_id": 3470545909,
  "path": "src/components/LessonNavigationButtons.tsx",
  "line": 26,
  "body": "Consider adding error handling here...",
  "html_url": "https://github.com/NeoLabHQ/learning-platform-app/pull/4#discussion_r2532291222",
  "created_at": "2025-11-16T22:40:46Z"
}

Adding Multiple Line-Specific Comments Together

To add multiple comments across different files in a single review, use the /reviews endpoint with JSON input.

Why Use Reviews for Multiple Comments?

• Atomic operation - All comments are added together
• Single notification - Doesn't spam with multiple notifications
• Better UX - Appears as one cohesive review
• Same mechanism as GitHub UI - "Start a review" → "Finish review"

Basic Syntax

cat <<'EOF' | gh api repos/{owner}/{repo}/pulls/{pr_number}/reviews --input -
{
  "event": "COMMENT",
  "body": "Overall review summary (optional)",
  "comments": [
    {
      "path": "file1.tsx",
      "body": "Comment on file 1",
      "side": "RIGHT",
      "line": 15
    },
    {
      "path": "file2.tsx",
      "body": "Comment on file 2",
      "side": "RIGHT",
      "line": 30
    }
  ]
}
EOF

Review Event Types

Complete Example

cat <<'EOF' | gh api repos/NeoLabHQ/learning-platform-app/pulls/4/reviews --input -
{
  "event": "COMMENT",
  "body": "Testing multiple line-specific comments via gh api",
  "comments": [
    {
      "path": "src/components/CourseCard.tsx",
      "body": "Test comment generated by Claude",
      "side": "RIGHT",
      "line": 15
    },
    {
      "path": "src/components/CourseProgressWidget.tsx",
      "body": "Test comment generated by Claude",
      "side": "RIGHT",
      "line": 30
    },
    {
      "path": "src/components/LessonProgressTracker.tsx",
      "body": "Test comment generated by Claude",
      "side": "RIGHT",
      "line": 20
    }
  ]
}
EOF

Response

{
  "id": 3470546747,
  "state": "COMMENTED",
  "html_url": "https://github.com/NeoLabHQ/learning-platform-app/pull/4#pullrequestreview-3470546747",
  "submitted_at": "2025-11-16T22:42:43Z",
  "commit_id": "e152d0dd6cf498467eadbeb638bf05abe11c64d4"
}

Common Issues and Solutions

Issue 1: "user_id can only have one pending review per pull request"

Error Message:

gh: Validation Failed (HTTP 422)
{"message":"Validation Failed","errors":[{"resource":"PullRequestReview","code":"custom","field":"user_id","message":"user_id can only have one pending review per pull request"}]}

Cause: GitHub only allows one pending (unsubmitted) review per user per PR. If you previously started a review through the UI or API and didn't submit it, it blocks new review creation.

Solution 1: Submit the pending review

# Check for pending reviews
gh api repos/{owner}/{repo}/pulls/{pr_number}/reviews | jq '.[] | select(.state=="PENDING")'

# Submit it through the UI or ask the user to submit it

Solution 2: Use the single comment endpoint instead

# Add individual comments without creating a review
gh api repos/{owner}/{repo}/pulls/{pr_number}/comments \
  -f body='Comment text' \
  -f commit_id='<sha>' \
  -f path='file.tsx' \
  -F line=26 \
  -f side='RIGHT'

Issue 2: Array syntax not working with --raw-field

Failed Attempt:

# This does NOT work - GitHub API receives an object, not an array
gh api repos/{owner}/{repo}/pulls/{pr}/reviews \
  --raw-field 'comments[0][path]=file1.tsx' \
  --raw-field 'comments[0][line]=15' \
  --raw-field 'comments[1][path]=file2.tsx' \
  --raw-field 'comments[1][line]=30'

Error:

Invalid request. For 'properties/comments', {"0" => {...}, "1" => {...}} is not an array.

Solution: Use JSON input via heredoc:

cat <<'EOF' | gh api repos/{owner}/{repo}/pulls/{pr}/reviews --input -
{
  "comments": [...]
}
EOF

Issue 3: Invalid line number

Error Message:

Pull request review thread line must be part of the diff

Cause: The line number doesn't exist in the diff for this file.

Solutions:

• Verify the file was actually changed in this PR
• Check the "Files changed" tab to see actual line numbers in the diff
• Ensure you're using the correct commit_id (the latest commit in the PR)

Issue 4: Wrong commit_id

Error Message:

commit_sha is not part of the pull request

Solution: Get the latest commit SHA:

gh api repos/{owner}/{repo}/pulls/{pr_number} --jq '.head.sha'

Best Practices

1. Get PR Information First

Before adding comments, gather necessary information:

# Get PR details
gh pr view {pr_number} --json headRefOid,files

# Or use the API
gh api repos/{owner}/{repo}/pulls/{pr_number} --jq '{commit: .head.sha, files: [.changed_files]}'

# List files changed
gh api repos/{owner}/{repo}/pulls/{pr_number}/files --jq '.[] | {filename: .filename, additions: .additions, deletions: .deletions}'

2. Check for Pending Reviews

# Check if you have a pending review
gh api repos/{owner}/{repo}/pulls/{pr_number}/reviews \
  --jq '.[] | select(.state=="PENDING" and .user.login=="YOUR_USERNAME")'

3. Use Meaningful Comment Text

• Be specific and constructive
• Reference documentation or best practices
• Suggest alternatives when requesting changes
• Use code blocks for code suggestions:

Consider using async/await:

\`\`\`typescript
async function getData() {
  const result = await fetch(url);
  return result.json();
}
\`\`\`

4. Batch Related Comments

Use the review endpoint to group related comments:

• All comments for a single file/area
• All comments for a specific concern (security, performance, etc.)
• Complete review session

5. Choose the Right Event Type

# For feedback during development
"event": "COMMENT"

# When approving
"event": "APPROVE"

# When blocking merge
"event": "REQUEST_CHANGES"

Workflow Examples

Example 1: Quick Single Comment

#!/bin/bash
OWNER="NeoLabHQ"
REPO="learning-platform-app"
PR=4

# Get latest commit
COMMIT=$(gh api repos/$OWNER/$REPO/pulls/$PR --jq '.head.sha')

# Add comment
gh api repos/$OWNER/$REPO/pulls/$PR/comments \
  -f body='Consider extracting this into a separate function for better testability' \
  -f commit_id="$COMMIT" \
  -f path='src/utils/validation.ts' \
  -F line=45 \
  -f side='RIGHT'

Example 2: Comprehensive Review

#!/bin/bash
OWNER="NeoLabHQ"
REPO="learning-platform-app"
PR=4

# Create review with multiple comments
cat <<EOF | gh api repos/$OWNER/$REPO/pulls/$PR/reviews --input -
{
  "event": "COMMENT",
  "body": "Thanks for the PR! I've reviewed the changes and have a few suggestions.",
  "comments": [
    {
      "path": "src/components/CourseCard.tsx",
      "body": "Consider memoizing this component to prevent unnecessary re-renders",
      "side": "RIGHT",
      "line": 25
    },
    {
      "path": "src/utils/courseProgress.ts",
      "body": "This function could benefit from error handling for invalid course IDs",
      "side": "RIGHT",
      "line": 12
    },
    {
      "path": "src/state/CourseProgressState.ts",
      "body": "Consider adding JSDoc comments to document the expected behavior",
      "side": "RIGHT",
      "line": 8
    }
  ]
}
EOF

Example 3: Multi-line Comment

# Comment on a range of lines (e.g., lines 10-15)
gh api repos/$OWNER/$REPO/pulls/$PR/comments \
  -f body='This entire block could be simplified using array destructuring' \
  -f commit_id="$COMMIT" \
  -f path='src/utils/parser.ts' \
  -F start_line=10 \
  -f start_side='RIGHT' \
  -F line=15 \
  -f side='RIGHT'

Helpful Helper Scripts

Get PR Files and Lines

#!/bin/bash
# pr-files.sh - List all files changed in a PR with line counts

OWNER="$1"
REPO="$2"
PR="$3"

gh api repos/$OWNER/$REPO/pulls/$PR/files --jq '.[] | "\(.filename): +\(.additions)/-\(.deletions)"'

Check Review Status

#!/bin/bash
# check-reviews.sh - Check review status for a PR

OWNER="$1"
REPO="$2"
PR="$3"

echo "=== Reviews ==="
gh api repos/$OWNER/$REPO/pulls/$PR/reviews --jq '.[] | "\(.user.login): \(.state) at \(.submitted_at)"'

echo -e "\n=== Pending Reviews ==="
gh api repos/$OWNER/$REPO/pulls/$PR/reviews --jq '.[] | select(.state=="PENDING") | "\(.user.login): \(.state)"'

Related Documentation

• GitHub API: Pull Request Review Comments
• GitHub API: Pull Request Reviews
• GitHub CLI Manual
• Create PR Command
• Commit Command

API Reference

POST /repos/{owner}/{repo}/pulls/{pull_number}/comments

Creates a review comment on a specific line.

Endpoint: https://api.github.com/repos/{owner}/{repo}/pulls/{pull_number}/comments

Parameters:

• body (string, required): Comment text
• commit_id (string, required): SHA of commit
• path (string, required): Relative file path
• line (integer, required): Line number in diff
• side (string, required): "LEFT" or "RIGHT"
• start_line (integer, optional): Start line for multi-line
• start_side (string, optional): Start side for multi-line

POST /repos/{owner}/{repo}/pulls/{pull_number}/reviews

Creates a review with optional line-specific comments.

Endpoint: https://api.github.com/repos/{owner}/{repo}/pulls/{pull_number}/reviews

Parameters:

• event (string, required): "APPROVE", "REQUEST_CHANGES", or "COMMENT"
• body (string, optional): Overall review comment
• comments (array, optional): Array of comment objects
• commit_id (string, optional): SHA of commit to review

Comment Object:

• path (string, required): Relative file path
• body (string, required): Comment text
• line (integer, required): Line number in diff
• side (string, required): "LEFT" or "RIGHT"
• start_line (integer, optional): Start line for multi-line
• start_side (string, optional): Start side for multi-line