instructure/canvas-lms · error · FieldTooLongError

# is too long, max length is # characters

Error message

#{type} is too long, max length is #{max} characters

What it means

Quizzes::QuizQuestion::RawFields#check_length raises FieldTooLongError when an HTML field (question text, answer HTML, comment, etc.) exceeds its configured maximum length. It is a guard used by fetch_with_enforced_length to prevent oversized quiz question fields from being persisted.

Solutions

1. Shorten the offending HTML field (question text, answers, or comments) below the max length
2. Strip or compress the HTML (remove styles/scripts, convert to plain text) before importing
3. For migrations, pre-process QTI/CSV content to truncate or split oversized fields
4. If legitimate content needs more space, request a limit adjustment for the field type

Example fix

// before
question_text = long_html_string
// after
question_text = long_html_string[0, QuizQuestion::MAX_QUESTION_LENGTH]

raise if question_text && question_text.length > 15_000
answer_html.each { |a| raise if a.length > max_answer_length }

def field_within_limit?(html, max)
  html.nil? || html.length <= max
end

begin
  fields = quiz_question.fetch_with_enforced_length
rescue Quizzes::QuizQuestion::RawFields::FieldTooLongError => e
  # truncate source content and retry, or surface a validation message
end

When it happens

Trigger: Fetching raw fields of a quiz question where question_text, answer_html, or comment_html exceeds the per-type max length — typically when a question was imported from QTI/external content or built via API with very long HTML.

Common situations: Migrating quiz banks from other LMSs with larger field limits; pasting large rich-text/HTML into question or answer editors; API/CSV imports without length checks; older questions that predate the limit.

Understand the failure class

Background: payload too large / request exceeds maximum size: why libraries cap bytes and how to fix oversize payloads — this error's family across 50 libraries.

Related errors

• A maximum of 50 assessees can be provided at once
• A maximum of 50 assessors can be provided at once
• COUNT must be <=
• pseudonym cannot have a unique_id of length #
• and cannot be used together

AI-assisted analysis of instructure/canvas-lms@1c9f0bb801 (2026-09-15). Data as JSON: /api/errors/fbaca8bfbbb830c6. Report an issue: GitHub.

Appendix: source

Thrown at app/models/quizzes/quiz_question/raw_fields.rb:54

    end
  end

  def fetch_with_enforced_length(key, opts = {})
    default = opts.fetch(:default, "")
    max_size = opts.fetch(:max_size, 16.kilobytes)

    check_length(fetch_any(key, default), key_to_type(key), max_size)
  end

  def sanitize(html)
    Sanitize.clean(html || "", CanvasSanitize::SANITIZE)
  end

  private

  def check_length(html, type, max)
    if html && html.length > max
      raise FieldTooLongError, "#{type} is too long, max length is #{max} characters"
    end

    html
  end

  def key_to_type(key)
    key.to_s.humanize.downcase
  end
end

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