remix-run/remix · error · Error

invalid bypass pattern ${JSON.stringify(pattern)}: "{$}" is

Error message

invalid bypass pattern ${JSON.stringify(pattern)}: "{$}" is not supported in cop-middleware

What it means

cop-middleware deliberately does not support the '{$}' catch-all dollar wildcard that other Remix routing layers may recognize. parseBypassSegment throws when a wildcard's name is exactly '$'. Bypass patterns in cop-middleware use '{name...}' tail wildcards instead.

Source

Thrown at packages/cop-middleware/src/lib/cop.ts:288

  if (segment === '') {
    throw new Error(
      `invalid bypass pattern ${JSON.stringify(pattern)}: empty path segments are not allowed`,
    )
  }

  if (!segment.startsWith('{') || !segment.endsWith('}')) {
    return { type: 'static', value: segment }
  }

  let wildcardName = segment.slice(1, segment.length - 1)
  if (wildcardName === '') {
    throw new Error(
      `invalid bypass pattern ${JSON.stringify(pattern)}: empty wildcards are not allowed`,
    )
  }

  if (wildcardName === '$') {
    throw new Error(
      `invalid bypass pattern ${JSON.stringify(pattern)}: "{$}" is not supported in cop-middleware`,
    )
  }

  if (wildcardName.endsWith('...')) {
    if (!isLastSegment) {
      throw new Error(
        `invalid bypass pattern ${JSON.stringify(pattern)}: tail wildcards must be last`,
      )
    }

    if (wildcardName.length === 3) {
      throw new Error(
        `invalid bypass pattern ${JSON.stringify(pattern)}: tail wildcards require a name`,
      )
    }

    return { type: 'rest' }

View on GitHub (pinned to 9696913134)

Solutions

Replace '{$}' with a named tail wildcard: '/legacy/{rest...}'
Review cop-middleware docs for supported wildcard syntax ({name} and {name...})

Example fix

// before
cop.addInsecureBypassPattern('/legacy/{$}')
// after
cop.addInsecureBypassPattern('/legacy/{rest...}')

Defensive patterns

Strategy: validation

Validate before calling

if (pattern.includes('{$}')) throw new Error('use {name...} instead of {$}')

Type guard

const usesSupportedWildcards = (p: string) => !p.includes('{$}')

Prevention

Do not copy route-config syntax into bypass patterns
Keep a cheat sheet of cop-middleware wildcard syntax in the config module

When it happens

Trigger: addInsecureBypassPattern('/legacy/{$}') or any pattern with a '{$}' segment, often copied from Remix route config or other route-matching syntax.

Common situations: Porting route patterns from Remix's pathless/catch-all route syntax into cop-middleware bypass config; assuming shared wildcard syntax across routing libraries.

Related errors

AI-assisted analysis of remix-run/remix@9696913134 (2026-08-27). Data as JSON: /api/errors/0bfec70dbdeb8785. Report an issue: GitHub.