What causes "MCP import preview failed" in Hmbown/CodeWhale?

Check the source MCP config file exists, is readable, and parses as valid JSON/YAML.

MCP import preview failed

Error message

MCP import preview failed

What it means

Generic fallback error raised when the MCP import preview task completes but its inner operation returns Err — the actual preview failure detail is discarded (`Err(_)`) and replaced with this fixed message. The preview renders what an import would change (servers, config diff) before the user approves it.

Solutions

Check the source MCP config file exists, is readable, and parses as valid JSON/YAML.
Validate the file's schema against the expected MCP config format (server entries, required fields).
Retry the preview — the underlying error is swallowed, so verify the input rather than guessing from this message.
If the format is from a different tool/version, convert it to the native MCP config shape first.

Example fix

// before
Err(_) => Err(anyhow::anyhow!("MCP import preview failed")),
// after: keep the cause
Err(err) => Err(anyhow::anyhow!("MCP import preview failed: {err:#}")),

Defensive patterns

Strategy: validation

Validate before calling

// before requesting a preview, ensure the source parses
let text = std::fs::read_to_string(&import_path)?;
let parsed: serde_json::Value = serde_json::from_str(&text)
    .or_else(|_| serde_yaml::from_str(&text))?;
if parsed.get("servers").is_none() {
    eprintln!("import file has no 'servers' section");
}

Try / catch

match preview_import(&import_path).await {
    Ok(text) => show_preview(text),
    Err(e) => show_error(format!("MCP import preview failed: {e:#}")),
}

Prevention

Validate the import file (exists, readable, valid JSON/YAML, `servers` present) before previewing.
Confirm the file matches the expected MCP config schema/version for this build.
Avoid hand-editing exported configs before import; import the original export.
Surface the inner error — the fixed message hides the real cause.

When it happens

Trigger: Requesting an MCP import preview (handle_mcp_ui_action ImportPreview path) where the awaited preview returns Err — e.g. unreadable or malformed source config, invalid JSON/YAML in the imported file, or an IO error reading the file.

Common situations: Importing an MCP config exported from another tool with a schema the parser rejects; pointing the import at a nonexistent path; permission errors reading the source file; newer/older config format version mismatch.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/6b8f0891cd8d0363. Report an issue: GitHub.

Appendix: source

Thrown at crates/tui/src/tui/ui/handlers.rs:806

        }
        crate::tui::app::McpUiAction::ImportList => {
            let path = path.clone();
            let workspace = app.workspace.clone();
            let plugins = app.plugin_registry.clone();
            #[cfg(test)]
            let ticket = crate::test_support::env_scope_ticket();
            match tokio::task::spawn_blocking(move || {
                #[cfg(test)]
                let _membership = crate::test_support::join_env_scope(ticket);
                mcp_external_import_status_text(&workspace, &path, plugins.as_ref())
            })
            .await
            {
                Ok(text) => {
                    message = Some(text);
                    Ok(())
                }
                Err(_) => Err(anyhow::anyhow!("MCP import preview failed")),
            }
        }
        crate::tui::app::McpUiAction::ImportApprove { name }
        | crate::tui::app::McpUiAction::ImportDecline { name } => {
            let approve = approve_import;
            let path = path.clone();
            let workspace = app.workspace.clone();
            let plugins = app.plugin_registry.clone();
            #[cfg(test)]
            let ticket = crate::test_support::env_scope_ticket();
            match tokio::task::spawn_blocking(move || {
                #[cfg(test)]
                let _membership = crate::test_support::join_env_scope(ticket);
                mcp_import_apply(&workspace, &path, plugins.as_ref(), &name, approve)
            })
            .await
            {
                Ok(Ok(msg)) => {

View on GitHub (pinned to 73e0f67d83)