A multi-line review comment requires both startLine and star

Error message

A multi-line review comment requires both startLine and startSide.

What it means

GitHub multi-line review comments require both startLine and startSide; the integration enforces that they are either both present or both absent, throwing on the asymmetric case (XOR of the two being undefined).

Source

Thrown at mastracode/factory/src/integrations/github/integration.ts:944

  }

  async #createReviewComment(input: InputOf<'createReviewComment'>) {
    const { octokit, parts } = this.#repositoryClient(input.connection, input.sourceId);
    const pullNumber = requirePullRequestNumber(input.pullRequestId);
    if (input.replyToId) {
      const { data } = await octokit.pulls.createReplyForReviewComment({
        ...parts,
        pull_number: pullNumber,
        comment_id: requirePositiveId(input.replyToId, 'review comment'),
        body: input.body,
      });
      return parseReviewComment(data);
    }
    if (!input.commitId || !input.path || input.line === undefined || !input.side) {
      throw new Error('A review comment requires commitId, path, line, and side unless it is a reply.');
    }
    if ((input.startLine === undefined) !== (input.startSide === undefined)) {
      throw new Error('A multi-line review comment requires both startLine and startSide.');
    }
    const { data } = await octokit.pulls.createReviewComment({
      ...parts,
      pull_number: pullNumber,
      body: input.body,
      commit_id: input.commitId,
      path: input.path,
      line: input.line,
      side: input.side.toUpperCase() as 'LEFT' | 'RIGHT',
      start_line: input.startLine,
      start_side: input.startSide?.toUpperCase() as 'LEFT' | 'RIGHT' | undefined,
    });
    return parseReviewComment(data);
  }

  async #updateReviewComment(input: InputOf<'updateReviewComment'>) {
    const { octokit, parts } = this.#repositoryClient(input.connection, input.sourceId);
    const { data } = await octokit.pulls.updateReviewComment({

View on GitHub (pinned to 75dd419e61)

Solutions

Supply both startLine and startSide together when creating multi-line comments
Set neither field for single-line comments
Validate the pair (both-or-neither) at the caller before invoking the integration

Example fix

// before
await gh.createReviewComment({ ..., commitId, path, line: 50, side: 'RIGHT', startLine: 45 }); // startSide missing
// after
await gh.createReviewComment({ ..., commitId, path, line: 50, side: 'RIGHT', startLine: 45, startSide: 'RIGHT' });

Defensive patterns

Strategy: validation

Validate before calling

if ((input.startLine === undefined) !== (input.startSide === undefined)) {
  throw new Error('multi-line review comment requires both startLine and startSide (or neither)');
}

Try / catch

try {
  await gh.createReviewComment(input);
} catch (e) {
  if (e.message.startsWith('A multi-line review comment requires both startLine')) {
    // add the missing startSide/startLine or drop both for a single-line comment
  } else throw e;
}

Prevention

Group startLine/startSide into a single optional range object in your input types
Toggle both fields together in comment-form UI state
Add a shared validator used by every code path that builds review-comment payloads

When it happens

Trigger: Creating a review comment where startLine is set but startSide is undefined (or vice versa) — the API payload would be rejected by GitHub as incomplete range specification.

Common situations: UIs that let users pick an end line but forget the range start side; code that copies startLine from one comment template but not startSide; SIDE differences when spanning LEFT/RIGHT sides of a diff.

Understand the failure class

Background: "Missing required field" and "field is required" errors: why libraries reject payloads that omit mandatory fields — this error's family across 20 libraries.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/f52bdc47718ffc92. Report an issue: GitHub.