---
name: "throw"
section: "3tcl"
platform: "linux"
package: "tcl8.6-doc"
version: "8.6.16+dfsg-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/throw"
---

# throw(3tcl)

Generate a machine-readable error

```

```

## NAME

throw - Generate a machine-readable error

## SYNOPSIS

**throw** *type message*

```

```

## DESCRIPTION

This command causes the current evaluation to be unwound with an error. The error created is described by the *type* and *message* arguments: *type* must contain a list of words describing the error in a form that is machine-readable (and which will form the error-code part of the result dictionary), and *message* should contain text that is intended for display to a human being.

The stack will be unwound until the error is trapped by a suitable **catch** or **try** command. If it reaches the event loop without being trapped, it will be reported through the **bgerror** mechanism. If it reaches the top level of script evaluation in **tclsh**, it will be printed on the console before, in the non-interactive case, causing an exit (the behavior in other programs will depend on the details of how Tcl is embedded and used).

By convention, the words in the *type* argument should go from most general to most specific.

## EXAMPLES

The following produces an error that is identical to that produced by **expr** when trying to divide a value by zero.

```
throw {ARITH DIVZERO {divide by zero}} {divide by zero}
```

## SEE ALSO

[catch(3tcl)](/catch/3tcl.md), [error(3tcl)](/error/3tcl.md), [errorCode(3tcl)](/errorCode/3tcl.md), [errorInfo(3tcl)](/errorInfo/3tcl.md), [return(3tcl)](/return/3tcl.md), [try(3tcl)](/try/3tcl.md)

## KEYWORDS

error, exception