unknown field ' ' for built-in provider ' ': expected one…

Error message

unknown field '{field_key}' for built-in provider '{provider_id}': expected one of api_key, base_url, model, context_window, mode, auth_mode, insecure_skip_tls_verify, http_headers, path_suffix

What it means

The config crate rejects any field assignment against a built-in provider (a provider whose config id is reserved, via is_builtin_provider_config_id). Built-ins only accept a fixed whitelist of override fields (api_key, base_url, model, context_window, mode, auth_mode, insecure_skip_tls_verify, http_headers, path_suffix); any other key in a [providers.<builtin>] table is refused before parsing so typos fail loudly instead of being silently ignored.

Solutions

Use one of the accepted fields: api_key, base_url, model, context_window, mode, auth_mode, insecure_skip_tls_verify, http_headers, path_suffix
Fix the field spelling to match the whitelist exactly (snake_case)
If you need arbitrary fields (e.g. kind, vendor), define a custom provider id instead of configuring the built-in
Check the docs for the current field list — the whitelist is version-specific

Example fix

// before
codewhale config set providers.openai.kind openai-compatible
// after
codewhale config set providers.openai.base_url https://api.openai.example/v1

Defensive patterns

Strategy: validation

Validate before calling

const BUILTIN_FIELDS: [&str; 9] = ["api_key","base_url","model","context_window","mode","auth_mode","insecure_skip_tls_verify","http_headers","path_suffix"];
if is_builtin_provider_config_id(provider_id) && !BUILTIN_FIELDS.contains(&field_key) {
    return Err(format!("{field_key} not allowed for built-in provider {provider_id}"));
}

Type guard

fn is_builtin_field(field: &str) -> bool {
    matches!(field, "api_key"|"base_url"|"model"|"context_window"|"mode"|"auth_mode"|"insecure_skip_tls_verify"|"http_headers"|"path_suffix")
}

Try / catch

match config.set_provider_config_value(provider_id, field_key, value) {
    Err(e) if e.to_string().contains("unknown field") => eprintln!("bad field {field_key}; use api_key/base_url/model/..."),
    other => other?,
}

Prevention

Keep the field whitelist in a shared constant next to your setters
Validate provider config tables at load time with a schema
Distinguish built-in vs custom provider ids in your config UI
Test config writes for both provider classes

When it happens

Trigger: Calling set_provider_config_value / `codewhale config set providers.<builtin-id>.<field> <value>` with a field_key not in the whitelist — typically a typo (apikey, api-key), a custom-provider-only field like kind or vendor, or an invented key.

Common situations: Hand-editing config.toml or scripting `config set` for a built-in provider using field names valid for custom providers; copying a custom provider block and renaming the id without removing unsupported fields; version drift where a field existed for built-ins in an older release but was removed.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/217fb90fd337ce42. Report an issue: GitHub.

Appendix: source

Thrown at crates/config/src/lib.rs:2572

            .entry(provider_id.to_string())
            .or_insert_with(|| toml::Value::Table(toml::value::Table::new()));
        entry.as_table_mut().with_context(|| {
            format!("custom provider '{provider_id}' must be a [providers.{provider_id}] table")
        })
    }

    /// Write one leg of a custom provider table. Named custom providers are
    /// not in [`ProviderKind::ALL`], so without this path
    /// `config set providers.<custom>.<field>` fell through to a literal
    /// top-level extras key and silently never took effect (#5167).
    fn set_custom_provider_value(
        &mut self,
        provider_id: &str,
        field_key: &str,
        value: &str,
    ) -> Result<()> {
        if is_builtin_provider_config_id(provider_id) {
            bail!(
                "unknown field '{field_key}' for built-in provider '{provider_id}': \
                 expected one of api_key, base_url, model, context_window, mode, auth_mode, \
                 insecure_skip_tls_verify, http_headers, path_suffix"
            );
        }
        if field_key == "kind" {
            let compatible =
                value.trim().to_ascii_lowercase().replace('_', "-") == "openai-compatible";
            if !compatible {
                bail!(
                    "custom provider '{provider_id}' must set [providers.{provider_id}].kind = \"openai-compatible\""
                );
            }
            self.custom_provider_table_mut(provider_id)?.insert(
                "kind".to_string(),
                toml::Value::String(value.trim().to_string()),
            );
            return Ok(());

View on GitHub (pinned to 73e0f67d83)