jdx/mise · error

brew-cask: unsupported tap URL for '{name}'; only GitHub tap

Error message

brew-cask: unsupported tap URL for '{name}'; only GitHub tap URLs can be fetched directly

What it means

The cask twin of the formula tap error: to fetch a third-party cask's JSON without the brew CLI, mise derives a raw.githubusercontent.com base from the tap (tap_raw_base). When a tap URL is configured but isn't a plain https://github.com/<owner>/<repo> URL, no base can be derived and mise refuses rather than guessing.

Source

Thrown at src/system/packages/brew/cask.rs:848

    }
}

async fn fetch_cask(req: &PackageRequest) -> Result<Cask> {
    let name = &req.name;
    let (requested_token, official_api) = match split_tap_name(name) {
        Some(("homebrew", "cask", token)) => (token, true),
        Some((_, _, token)) => (token, false),
        None => (name.as_str(), true),
    };
    validate_cask_path_component("requested token", requested_token)?;
    let (url, raw_base) = match split_tap_name(name) {
        Some(("homebrew", "cask", token)) => (
            format!("{API_BASE}/cask/{token}.json"),
            Some(HOMEBREW_CASK_RAW.to_string()),
        ),
        Some((owner, tap, token)) => {
            let Some(base) = super::api::tap_raw_base(owner, tap, req.tap_url.as_deref()) else {
                bail!(
                    "brew-cask: unsupported tap URL for '{name}'; only GitHub tap URLs can be fetched directly"
                );
            };
            (
                format!("{base}/api/cask/{token}.json"),
                Some(base.trim_end_matches("/HEAD").to_string()),
            )
        }
        None => (
            format!("{API_BASE}/cask/{name}.json"),
            Some(HOMEBREW_CASK_RAW.to_string()),
        ),
    };
    let mut cask = HTTP_FETCH
        .json_cached::<Cask, _>(url)
        .await
        .wrap_err_with(|| {
            format!(

View on GitHub (pinned to 9dcfcaa0dc)

Solutions

1. Point the tap at its bare GitHub repo URL: https://github.com/<owner>/<repo>
2. Drop the URL override — the owner/homebrew-<tap> convention is inferred automatically
3. For non-GitHub taps, install the cask with the brew CLI outside mise

Example fix

# before
[bootstrap.brew.taps]
"myorg/casks" = "git@github.com:myorg/homebrew-casks.git"

# after
[bootstrap.brew.taps]
"myorg/casks" = "https://github.com/myorg/homebrew-casks"

fn is_bare_github_url(url: &str) -> bool {
    let u = url.trim_end_matches(".git").trim_end_matches('/');
    match u.strip_prefix("https://github.com/") {
        Some(rest) => rest.split('/').count() == 2,
        None => false,
    }
}
// validate req.tap_url before fetching a tapped cask

Catch the 'unsupported tap URL' bail and report the configured tap entry: only bare GitHub https URLs are supported for direct cask metadata fetching.

When it happens

Trigger: Requesting `brew-cask:owner/tap/token` while the configured tap URL (in [bootstrap.brew.taps]) is non-GitHub (GitLab, self-hosted), an SSH URL, or contains extra path components such as /tree/main.

Common situations: Internal GitLab mirrors of taps; copy-pasted clone URLs; taps hosted outside GitHub entirely.

Related errors

• brew: tapped formula '{name}' needs a GitHub tap URL in [boo
• brew casks are installed at their current version ('{p}')
• brew-cask:{}: dependency cycle detected
• brew-cask:{}: Homebrew owns this cask; remove it with Homebr
• brew-cask:{}: conflicts with installed cask {}

AI-assisted analysis of jdx/mise@9dcfcaa0dc (2026-08-17). Data as JSON: /api/errors/e69b162a137f926a. Report an issue: GitHub.