entrypoint must be a string or array of strings, got %T

Error message

entrypoint must be a string or array of strings, got %T

What it means

The `entrypoint` TOML unmarshaler only supports a string or an array of strings; any other TOML type (integer, table, boolean) is rejected with this error. It fires while decoding the `build.entrypoint` key of the config.

Source

Thrown at runner/config.go:84

	case nil:
		*e = nil
		return nil
	case string:
		*e = []string{val}
		return nil
	case []interface{}:
		values := make([]string, len(val))
		for i, raw := range val {
			s, ok := raw.(string)
			if !ok {
				return fmt.Errorf("entrypoint values must be strings, got %T", raw)
			}
			values[i] = s
		}
		*e = values
		return nil
	default:
		return fmt.Errorf("entrypoint must be a string or array of strings, got %T", v)
	}
}

func (e entrypoint) binary() string {
	if len(e) == 0 {
		return ""
	}
	return e[0]
}

func (e entrypoint) args() []string {
	if len(e) <= 1 {
		return nil
	}
	return e[1:]
}

type cfgBuildOverrides struct {

View on GitHub (pinned to 71ea1dee05)

Solutions

Set entrypoint to a string: entrypoint = "./tmp/main"
Or an array of strings: entrypoint = ["./tmp/main", "arg1"]
If migrating from `bin`, use entrypoint = ["./tmp/main"] rather than a table

Example fix

// before (.air.toml)
entrypoint = { bin = "./tmp/main" }
// after (.air.toml)
entrypoint = ["./tmp/main"]

Defensive patterns

Strategy: validation

Validate before calling

// entrypoint must be a string or array of strings in TOML
// entrypoint = "./tmp/main"            ✓
// entrypoint = ["./tmp/main", "-flag"]  ✓
// entrypoint = 42 / true / {..}         ✗

Prevention

Only use string or [string] forms for entrypoint
Do not try to express entrypoint as a table
Validate the TOML with a linter before running air

When it happens

Trigger: A `.air.toml` with `entrypoint = 42`, `entrypoint = true`, or `entrypoint = {bin="./tmp/main"}` — any value that is neither string nor array — passed to UnmarshalTOML.

Common situations: Migrating from the deprecated `bin` key by writing `entrypoint` as a table; typo-pasting YAML/JSON style config into TOML; missing quotes causing TOML to parse the value as something else.

Related errors

AI-assisted analysis of air-verse/air@71ea1dee05 (2026-08-31). Data as JSON: /api/errors/6ea8a39b45e7caca. Report an issue: GitHub.