GitHub · Pull requests · REST API · Checked October 25, 2026

GitHub: why a comment on lines was refused

A comment on lines of a pull request goes to POST /repos/OWNER/REPO/pulls/NUMBER/comments with body, commit_id, path, line and side, and for a range of lines also start_line and start_side. GitHub's documentation names the statuses: 201 when the comment is created, 403 when you may not, and 422 when the request fails validation or the endpoint has been spammed. It does not list the 422 messages; the ones below are quoted from public reports, with GitHub's documented rules behind them (checked October 25, 2026).

HTTP/1.1 422 Unprocessable Entity

{"message":"Validation Failed","errors":[{"resource":"PullRequestReviewComment","code":"custom","field":"pull_request_review_thread.line","message":"pull_request_review_thread.line must be part of the diff"},{"resource":"PullRequestReviewComment","code":"missing_field","field":"pull_request_review_thread.diff_hunk"}],"documentation_url":"https://docs.github.com/rest/pulls/comments#create-a-review-comment-for-a-pull-request","status":"422"}

422: what GitHub says, and why

pull_request_review_thread.line must be part of the diff (with pull_request_review_thread.diff_hunk missing_field): the line is in none of the hunks of the file's diff. GitHub takes a comment only on the lines the diff shows, the changed lines and the few unchanged lines around them, as Files changed shows them. A line further away is refused, although the file is in the pull request.
side picks which file the line number counts in: GitHub's documentation says to use LEFT for deleted lines, and RIGHT for added lines and the unchanged lines around them. With LEFT, line is a line of the file before the change; a number that is only right on the new side lands outside the diff.
pull_request_review_thread.path invalid (with diff_hunk missing_field): GitHub did not take path as a file of the pull request's diff.
Pull request review thread start line must be part of the same hunk as the line: the range's first line (start_line) and last line (line) are in two different hunks. A range must sit inside one hunk.
pull_request_review_thread.start_line must precede the end line.: start_line is the same as line, or after it; a comment on one line goes with line alone. A public report got the same words for a range of deleted lines (side LEFT) sent without start_side, which GitHub's documentation requires for a comment on several lines.
In a review (POST /repos/OWNER/REPO/pulls/NUMBER/reviews with comments), the same rule has been reported as Unprocessable Entity with Pull request review thread line must be part of the diff and Pull request review thread diff hunk can't be blank, and one such comment fails the whole review.

403, 404

403 Resource not accessible by personal access token (or by integration): the token may read the pull request but not comment on it; a fine-grained token needs Pull requests read and write (see which permission to add).
403 or 429 for comments sent too fast: GitHub's documentation says that creating content too quickly with this endpoint may hit a secondary rate limit (see "API rate limit exceeded").
404: the repository or pull request is not there for this token, which is also how GitHub answers a private repository the token cannot see.
A reply to a line comment while you have a pending review answers user_id can only have one pending review per pull request (see why GitHub refused the review).

Taken, but outdated

commit_id is the commit the comment is about. GitHub's documentation says that a comment not on the latest commit may show as outdated when a later commit changes the line. position, the older way to name a line by its place in the diff, is closing down; line and side replace it.

What to do

Find the hunks: each file in GET /repos/OWNER/REPO/pulls/NUMBER/files has its patch. Every @@ -A,B +C,D @@ starts a hunk: B lines of the old file from line A, D lines of the new file from line C.
A line outside the diff: pick a line in or next to a change. To say something about the file as a whole, send subject_type file with path and no line; for the whole pull request, a conversation comment (POST /repos/OWNER/REPO/issues/NUMBER/comments).
A range across hunks: one comment for each hunk.
One line: line alone, without start_line. Deleted lines: side and start_side LEFT, with the old file's line numbers.
path: the path from the repository's root, as filename in the list of files gives it.

In IntelliJ IDEA: a comment only on the lines the diff carries, sent with GraphQL

How the GitHub support built into IntelliJ IDEA comments on lines of a pull request, in its source (checked October 31, 2026; IntelliJ IDEA: GHPRReviewDiffExtension.kt, GHPRReviewEditorGutterControlsState.kt, GHPRDiffReviewViewModel.kt, GHPRReviewNewCommentEditorViewModel.kt, GHPRReviewDataProviderImpl.kt, GHPRReviewServiceImpl.kt, createReview.graphql, addPullRequestReviewThread.graphql, GithubBundle.properties, CodeReviewSubmittableTextViewModel.kt):

Where it lets you comment: in the pull request's diff, the gutter offers a comment only on the lines of the diff's hunks (the changed lines and the unchanged lines around them that the diff carries), and only if your account has read permission or above on the repository, as GitHub reported when the IDE connected. A range of lines can be chosen only when both its ends are on such lines and on the same side, both in the old file or both in the new.
It does not use the REST endpoint above. With no pending review of yours, the comment box offers Add Single Comment and Start Review, the one you used last as the main button. Both send GitHub's GraphQL addPullRequestReview with the thread: path, line and side, for a range also startLine and startSide, and as commitOID the commit on the new side of the diff. Add Single Comment posts it at once as a review with COMMENT; Start Review keeps it in a pending review.
With a pending review of yours, Add Review Comment adds the thread to it with addPullRequestReviewThread. When the diff shows one commit rather than the whole pull request, it sends instead the line's old-style position in the diff between the merge base and that commit: as its source notes, the GraphQL threads cannot name a commit, and the REST endpoint cannot name the review and fails while a draft review exists.
When GitHub refuses, the comment box stays open with your text: it closes only after GitHub accepts the comment. The source also writes the error to the IDE's log.

GitHub pull requests in IntelliJ IDEA

Pull Request Inbox for GitHub, a plugin by Lesstep for JetBrains IDEs 2024.1 or later, comments on the lines you select in the IDE's diff. Before you type, it checks them against the hunks of the file's patch from GitHub, both ends of a range in one hunk on one side, and says so when they are outside. It sends line and side, and for a range also start_line and start_side on the same side; one line goes without start_line. commit_id is the head commit you had on screen. For a file without a patch, GitHub decides; when GitHub refuses, the plugin shows GitHub's words and puts your comment on the clipboard. The review inbox, diffs and conversations are free; approving, commenting and merging are Pro (US$1.50 a month, with a 30-day trial).

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