What causes "Invalid escape character at the end." in vercel/next.js?

Inspect NODE_OPTIONS and remove or fix the trailing backslash.

Invalid escape character at the end.

Error message

Invalid escape character at the end.

What it means

Thrown by tokenizeArgs when parsing NODE_OPTIONS (or any args string) and a backslash escape appears as the very last character inside a quoted string with no character following it. An escape needs a character to escape, so a trailing backslash is invalid.

Source

Thrown at packages/next/src/server/lib/utils.ts:81

 * values and escaped characters.
 * Converted from: https://github.com/nodejs/node/blob/c29d53c5cfc63c5a876084e788d70c9e87bed880/src/node_options.cc#L1401
 *
 * @param input The arguments string to be tokenized.
 * @returns An array of strings with the tokenized arguments.
 */
export const tokenizeArgs = (input: string): string[] => {
  let args: string[] = []
  let isInString = false
  let willStartNewArg = true

  for (let i = 0; i < input.length; i++) {
    let char = input[i]

    // Skip any escaped characters in strings.
    if (char === '\\' && isInString) {
      // Ensure we don't have an escape character at the end.
      if (input.length === i + 1) {
        throw new Error('Invalid escape character at the end.')
      }

      // Skip the next character.
      char = input[++i]
    }
    // If we find a space outside of a string, we should start a new argument.
    else if (char === ' ' && !isInString) {
      willStartNewArg = true
      continue
    }

    // If we find a quote, we should toggle the string flag.
    else if (char === '"') {
      isInString = !isInString
      continue
    }

    // If we're starting a new argument, we should add it to the array.

View on GitHub (pinned to 0ae8c72462)

Solutions

Inspect NODE_OPTIONS and remove or fix the trailing backslash.
Ensure any backslash inside a quoted NODE_OPTIONS value escapes a real following character.
Avoid backslashes in NODE_OPTIONS unless intentionally escaping a quote/space.

Example fix

# before
export NODE_OPTIONS='--max-old-space-size=4096 --title="app\'
# the trailing backslash is invalid

# after
export NODE_OPTIONS='--max-old-space-size=4096 --title="app"'

Defensive patterns

Strategy: validation

Validate before calling

function validateArgsString(input: string): void {
  if (/\\$/.test(input) || (/\\./.test(input) && input.endsWith('\\'))) {
    // crude check; better: ensure no backslash is the final char inside a quote
  }
}

Type guard

function hasTrailingEscape(input: string): boolean {
  // returns true if a backslash is the last char inside a quoted region
  let inStr = false
  for (let i = 0; i < input.length; i++) {
    if (input[i] === '\\' && inStr && i === input.length - 1) return true
    if (input[i] === '\\' && inStr) { i++; continue }
    if (input[i] === '"') inStr = !inStr
  }
  return false
}

Try / catch

try {
  tokenizeArgs(process.env.NODE_OPTIONS || '')
} catch (e) {
  if (e.message.includes('escape character')) {
    console.error('Fix NODE_OPTIONS: trailing backslash detected')
    process.exit(1)
  }
}

Prevention

Avoid trailing backslashes in NODE_OPTIONS.
Validate NODE_OPTIONS in a startup script.
Use shell line continuations outside quoted values.

When it happens

Trigger: The NODE_OPTIONS environment variable ends with a backslash inside a quoted value, e.g. NODE_OPTIONS='--title="foo\'. The tokenizer hits the backslash at i === input.length-1.

Common situations: Misconstructed NODE_OPTIONS in shell scripts, Docker ENV, or CI config where a trailing backslash escapes the closing quote or is left dangling. Shell line-continuation backslashes accidentally included.

Related errors

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/22a48894847f29ea. Report an issue: GitHub.