laravel/framework · error · InvalidArgumentException

Configuration value for key

Error message

Configuration value for key [%s] must be a string, %s given.

What it means

Thrown by Config\Repository::string(string $key) when the stored value is not a string (after applying any default). This is the typed config accessor introduced for strict retrieval; is_string($value) is checked and an InvalidArgumentException reports the key and the actual gettype(). A null result from a missing key (with no default) also triggers it because null is not a string.

Solutions

1. Provide a string default: Config::string('app.locale', 'en').
2. Ensure the underlying config/env value is a string (quote env values: APP_KEY='base64:...').
3. Use Config::get() if you need to tolerate non-string values, or cast at the source.

Example fix

// before
$locale = Config::string('app.locale');
// after
$locale = Config::string('app.locale', 'en');
// and in .env ensure: APP_LOCALE=en

$value = Config::get('app.locale');
if (! is_string($value)) {
    throw new \InvalidArgumentException('app.locale must be a string');
}

function configIsString(string $key): bool {
    return is_string(Config::get($key));
}

try {
    $locale = Config::string('app.locale');
} catch (\InvalidArgumentException $e) {
    $locale = 'en'; // safe fallback
}

When it happens

Trigger: Config::string('app.key') where app.key is null/missing/int/bool; reading an env-backed value that resolved to a non-string; providing a default that is itself not a string.

Common situations: An env var is unset so the config returns null; a config file stores an int/bool where a string was expected; typed accessor used during early bootstrap before config is loaded.

Related errors

• Configuration value for key
• Configuration value for key
• Collection should only include
• A driver must be specified.
• Ably error

AI-assisted analysis of laravel/framework@e0f6eb3518 (2026-08-11). Data as JSON: /api/errors/42f858169739475e. Report an issue: GitHub.

Appendix: source

Thrown at src/Illuminate/Config/Repository.php:95

        return $config;
    }

    /**
     * Get the specified string configuration value.
     *
     * @param  string  $key
     * @param  (\Closure():(string|null))|string|null  $default
     * @return string
     *
     * @throws \InvalidArgumentException
     */
    public function string(string $key, $default = null): string
    {
        $value = $this->get($key, $default);

        if (! is_string($value)) {
            throw new InvalidArgumentException(
                sprintf('Configuration value for key [%s] must be a string, %s given.', $key, gettype($value))
            );
        }

        return $value;
    }

    /**
     * Get the specified integer configuration value.
     *
     * @param  string  $key
     * @param  (\Closure():(int|null))|int|null  $default
     * @return int
     *
     * @throws \InvalidArgumentException
     */
    public function integer(string $key, $default = null): int
    {

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