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
   

2. 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	Type	Required	Description
body	string	Yes	The text of the review comment (supports Markdown)
commit_id	string	Yes	The SHA of the commit to comment on
path	string	Yes	Relative path to the file being commented on
line	integer	Yes	The line number in the diff (use -F for integers)
side	string	Yes	RIGHT for new/modified lines, LEFT for deleted lines
start_line	integer	No	For multi-line comments, the starting line
start_side	string	No	For multi-line comments, the starting side

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

Event	Description	When to Use
COMMENT	General review comment	Just leaving feedback without approval
APPROVE	Approve the PR	Changes look good, ready to merge
REQUEST_CHANGES	Request changes	Issues that must be fixed before merge

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