What causes "URL cannot be empty" in zeroclaw-labs/zeroclaw?

Pass a complete absolute URL ("https://example.com")

URL cannot be empty

Error message

URL cannot be empty

What it means

browser_open trims the raw url argument and rejects it if nothing remains. This is the first guard in validate_url; an empty URL cannot be allowlisted or opened, and failing closed here gives a clearer error than a downstream launcher failure.

Source

Thrown at crates/zeroclaw-tools/src/browser_open.rs:47

    ) -> anyhow::Result<Self> {
        Ok(Self {
            security,
            allowed_domains: domain_guard::normalize_allowed_domains(
                allowed_domains,
                "browser.allowed_domains",
            )?,
            allowed_private_hosts: domain_guard::normalize_allowed_domains(
                allowed_private_hosts,
                "browser.allowed_private_hosts",
            )?,
        })
    }

    fn validate_url(&self, raw_url: &str) -> anyhow::Result<String> {
        let url = raw_url.trim();

        if url.is_empty() {
            anyhow::bail!("URL cannot be empty");
        }

        if url.chars().any(char::is_whitespace) {
            anyhow::bail!("URL cannot contain whitespace");
        }

        if !(url.starts_with("https://") || url.starts_with("http://")) {
            anyhow::bail!("Only http:// or https:// URLs are allowed");
        }

        if self.allowed_domains.is_empty() && self.allowed_private_hosts.is_empty() {
            anyhow::bail!(
                "Browser tool is enabled but no allowed_domains are configured. Add [browser].allowed_domains in config.toml"
            );
        }

        let host = extract_host(url)?;
        let private_host = domain_guard::is_private_or_local_host(&host);

View on GitHub (pinned to 88bb9c8533)

Solutions

Pass a complete absolute URL ("https://example.com")
Make a missing URL a hard error at the call site instead of defaulting to an empty string
Trim and check is_empty() before invoking the tool

Example fix

// before
{"url": ""}
// after
{"url": "https://example.com"}

Defensive patterns

Strategy: validation

Validate before calling

let url = raw_url.trim();
if url.is_empty() {
    return Err("URL cannot be empty".into());
}

Try / catch

match open_tool.execute(args).await {
    Ok(res) if res.success => { /* ... */ }
    Ok(res) => {
        if res.error.as_deref().unwrap_or_default().contains("URL cannot be empty") {
            // fill in the URL at the source; do not retry with ""
        }
    }
    Err(e) => return Err(e),
}

Prevention

Reject empty URLs at the call site with a clear message
Never default missing URL parameters to an empty string

When it happens

Trigger: Calling the browser_open tool with url="", url=" ", or any value that is only whitespace after trim (e.g. a variable that was never filled in).

Common situations: Template or format! bugs producing an empty string; the model omitting the URL and caller code defaulting to ""; whitespace-only input from misparsed upstream configuration.

Related errors

AI-assisted analysis of zeroclaw-labs/zeroclaw@88bb9c8533 (2026-08-23). Data as JSON: /api/errors/7409792a4a971e1b. Report an issue: GitHub.