API:Errors and warnings: Difference between revisions

If something goes wrong in an API request, an error or a warning will be thrown (although the HTTP response will usually still be 200 OK). Warnings are thrown for non-fatal conditions such as invalid parameters, whereas errors are only thrown for fatal conditions.

Warnings are grouped by the name of the module that caused them. Multiple warnings from the same module are separated by a newline. In the legacy error formatting mode (see below), which is the default, warnings are output in the following format:

"warnings":{
"modulename":{
"*":"warning text"
}
}

(* will be replaced by warnings when formatversion=2 is used.)

When a non-legacy error formatting option is used, warnings are output in the same format as errors. E.g. with errorformat=wikitext the format will be:

"warnings":[
{
"code":"warning message key",
"*":"text of warning",
"module":"API module which caused the warning"
}
]

(* will be replaced with text when formatversion=2 is used.)

Since MediaWiki 1.29 errors are localizable, and available in multiple formats. An error (or warning) is expected to consist of a message, an error code (an arbitrary string, usually generated from the message key; see also #Standard error messages below), and optional extra data (an associative array). An API response with errors will look like this:

{
"errors":[
{
"code":"error-code",
/* ...error message..., */
"data":[/* ...any extra data... */],
"module":"path to the API module that generated the error"
},
/* ...more errors... */
],
"docref":"human-readable message on where to find help"
}

The data key in the output above will be missing if there is no extra data to display.

The way the error message in the output above is returned to the client is controlled by the errorformat API parameter. The various error formats available are:

"html":"the message, interpreted as wikitext and parsed into HTML"

"text":"the message as-is, with parameter substitution but without any parsing"

"text":"the message, like wikitext, but with added plaintext conversion"

"key":"message key",
"params":[/* ...message parameters... */]

For the formatting modes which involve message lookup (html, wikitext and plaintext) the API parameter errorlang can be used to set the language (only needed when different from the content language) and errorsuselocal to set whether the MediaWiki: namespace can be used to override default error messages.

Error codes are also returned in the MediaWiki-API-Error response HTTP header, separated by commas when there are multiple errors.

For an example error response or to test your client's error handling, visit https://en.wikipedia.org/w/api.php?action=blah&errorformat=plaintext&format=jsonfm&formatversion=2

When errorformat is not set (or set to bc), errors will be displayed in the legacy format instead.

In the legacy error format, there is always at most one error; additional ones are discarded. The response looks like this:

{
"error":{
"code":"error-code",
"info":"the message as-is, with parameter substitution but without any parsing",
/* ...any extra data... */
}
}

The extra data in the output above is spliced into the object instead of being under the data key.

Error messages are documented in this wiki as shown below, which corresponds to the json error response in #Legacy format above:

The various error messages are:

Some generic error messages are shared among modules. If a module can throw these errors, that's explicitly mentioned in its Possible errors section.

• All error and warning outputs above use format=json&formatversion=2. For formatversion=1, the field docref will be replaced by *.

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