What causes "No command provided in extension string" in aaif-goose/goose?

Append the server command after the env assignments: 'API_KEY=x node server.js'

No command provided in extension string

Error message

No command provided in extension string

What it means

Stdio extension strings have the shape 'KEY=VALUE cmd args...': leading tokens containing '=' are consumed as environment variables, and the next token becomes the command. parse_stdio_extension fails when, after consuming env assignments, no token remains to serve as the command.

Source

Thrown at crates/goose-cli/src/session/mod.rs:355

    }

    /// Parse a stdio extension command string into an ExtensionConfig
    /// Format: "ENV1=val1 ENV2=val2 command args..."
    pub fn parse_stdio_extension(extension_command: &str) -> Result<ExtensionConfig> {
        let mut parts = goose::utils::split_command_args(extension_command)?;
        let mut envs = HashMap::new();

        while let Some(part) = parts.first() {
            if !part.contains('=') {
                break;
            }
            let env_part = parts.remove(0);
            let (key, value) = env_part.split_once('=').unwrap();
            envs.insert(key.to_string(), value.to_string());
        }

        if parts.is_empty() {
            return Err(anyhow::anyhow!("No command provided in extension string"));
        }

        let cmd = parts.remove(0);
        let name = std::path::Path::new(&cmd)
            .file_name()
            .and_then(|f| f.to_str())
            .unwrap_or("unnamed")
            .to_string();

        Ok(ExtensionConfig::Stdio {
            name,
            cmd,
            args: parts,
            envs: Envs::new(envs),
            env_keys: Vec::new(),
            description: goose::config::DEFAULT_EXTENSION_DESCRIPTION.to_string(),
            timeout: Some(goose::config::DEFAULT_EXTENSION_TIMEOUT),
            cwd: None,

View on GitHub (pinned to 3810898a74)

Solutions

Append the server command after the env assignments: 'API_KEY=x node server.js'
Echo the extension string before passing it to goose to verify it expands as expected
Check for stray quotes or empty shell variables

Example fix

# before
goose session add-extension "API_KEY=$MY_TOKEN"
# after
goose session add-extension "API_KEY=$MY_TOKEN node /abs/path/mcp-server/build/index.js"

Defensive patterns

Strategy: validation

Validate before calling

fn has_command(ext: &str) -> bool {
    ext.split_whitespace().any(|p| !p.contains('='))
}

assert!(has_command(&extension_command), "extension string needs a command after KEY=VALUE parts");

Prevention

Always pair env assignments with the command token: 'KEY=VALUE cmd args'
Echo the final extension string after shell expansion before passing it to goose
Quote the whole extension string so word splitting happens inside goose only

When it happens

Trigger: goose add-extension / --with-extension / config strings such as 'FOO=bar' (env assignments only), an empty command after word splitting, or an unset shell variable that expanded to nothing.

Common situations: Quoting mistakes where only the env part survives; copy-pasted extension strings missing the binary; passing "API_KEY=$TOKEN" when $TOKEN is unset.

Related errors

AI-assisted analysis of aaif-goose/goose@3810898a74 (2026-08-16). Data as JSON: /api/errors/074469c6779d61c0. Report an issue: GitHub.