vitejs/vite · error · Error

The value passed to "base" option was malformed. It should b

Error message

The value passed to "base" option was malformed. It should be a valid URL.

What it means

In decodeBase (config.ts:2336-2343), Vite runs decodeURI on the resolved base value; if the value contains malformed percent-encoding (e.g. a stray '%' not forming a valid escape), decodeURI throws URIError which Vite re-wraps as 'The value passed to base option was malformed'. The base must be a valid, decodable URL/path.

Source

Thrown at packages/vite/src/node/config.ts:2340

  }

  // parse base when command is serve or base is not External URL
  if (!isBuild || !isExternal) {
    base = new URL(base, 'http://vite.dev').pathname
    // ensure leading slash
    if (base[0] !== '/') {
      base = '/' + base
    }
  }

  return base
}

function decodeBase(base: string): string {
  try {
    return decodeURI(base)
  } catch {
    throw new Error(
      'The value passed to "base" option was malformed. It should be a valid URL.',
    )
  }
}

export function sortUserPlugins(
  plugins: (Plugin | Plugin[])[] | undefined,
): [Plugin[], Plugin[], Plugin[]] {
  const prePlugins: Plugin[] = []
  const postPlugins: Plugin[] = []
  const normalPlugins: Plugin[] = []

  if (plugins) {
    plugins.flat().forEach((p) => {
      if (p.enforce === 'pre') prePlugins.push(p)
      else if (p.enforce === 'post') postPlugins.push(p)
      else normalPlugins.push(p)
    })

View on GitHub (pinned to 89620f09af)

Solutions

1. Correct the base to a valid path/URL, e.g. '/my-app/'.
2. Percent-encode any literal special characters properly (e.g. '%25' for a literal '%') or remove them.
3. Use an absolute URL or a simple leading-slash path as the docs recommend.

Example fix

// before
export default { base: '/vite%/' }
// after
export default { base: '/vite/' }

function assertValidBase(base: string) {
  try { decodeURI(base) } catch { throw new Error(`Malformed base: ${base}`) }
}

function isDecodableBase(base: string): boolean {
  try { decodeURI(base); return true } catch { return false }
}

When it happens

Trigger: Setting config base to a string containing an invalid percent sequence such as '/my%path/' or '/vite%/'.

Common situations: Passing a deployment prefix with a literal '%' (e.g. a versioned path), an unencoded query/fragment, or a copy-pasted URL with reserved characters.

Related errors

• `renderLegacyChunks` and `renderModernChunks` cannot be both
• Invalid environment name "${name}". Environment names must o
• `input` cannot contain glob characters. They are reserved, s
• Required environments configuration were stripped out in the
• Unsupported configLoader: ${configLoader}. Accepted values a

AI-assisted analysis of vitejs/vite@89620f09af (2026-08-03). Data as JSON: /data/errors/3254c4bfe863192d.json. Report an issue: GitHub.