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Applies to AppStream 1.0

6 Data Validation

These pages contain various information on AppStream metadata validation.

6.1 Validator Issues

6.1.1 Introduction

The AppStream utility appstreamcli validate can validate all kinds of AppSteeam XML metadata. It will emit a variety of hints with different priority:

Error hints render the data unusable or severely limit its usefulness and make it fail validation. Warnings warn about likely unintended behavior, typing errors or issues which might cause data to not be displayed or improperly read. They fail validation, but may be ignored in some circumstances. Info hints are optional recommendations to make the data better, while pedantic hints are nice-to-have. The latter are not displayed by default unless the tool is in pedantic mode.

This document contains a list of all issues checked for by appstreamcli validate.

6.1.2 Validator Issue Tags

This is a list of all possible validation issues that appstreamcli can detect.

type-property-required 

Severity: error

This tag requires a type property.

invalid-child-tag-name 

Severity: info

Tags of this name are not permitted in this section.

metainfo-localized-description-tag 

Severity: error

A <description/> tag must not be localized in metainfo files (upstream metadata). Localize the individual paragraphs instead.

catalog-localized-description-section 

Severity: error

This element (paragraph, list, etc.) of a <description/> tag must not be localized individually in catalog metadata. Localize the whole <description/> tag instead. The AppStream metadata catalog generator (e.g. `appstream-generator`) will already do the right thing when compiling the data.

description-markup-invalid 

Severity: error

AppStream descriptions support only a limited set of tags to format text: Paragraphs (<p/>) and lists (<ul/>, <ol/>). This description markup contains an invalid XML tag that would not be rendered correctly in applications supporting the metainfo specification.

description-para-markup-invalid 

Severity: error

This description paragraph contains invalid markup. Currently, only <em/> and <code/> are permitted.

description-enum-item-invalid 

Severity: error

Enumerations must only have list items (<li/>) as children.

description-first-para-too-short 

Severity: info

The first `description/p` paragraph of this component might be too short (< 80 characters). Please consider starting with a longer paragraph to improve how the description looks like in software centers and to provide more detailed information on this component immediately in the first paragraph.

description-first-word-not-capitalized 

Severity: info

The description line does not start with a capitalized word, project name or number.

description-has-plaintext-url 

Severity: warning

The description contains a web URL in plain text. This is not allowed, please use the <url/> tag instead to share links.

tag-not-translatable 

Severity: error

This tag is not translatable.

tag-duplicated 

Severity: error

This tag must only appear once in this context. Having multiple tags of this kind is not valid.

tag-empty 

Severity: warning

The mentioned tag is empty, which is highly likely not intended as it should have content.

tag-invalid-text-content 

Severity: error

The mentioned tag has text content, even though it must not contain text.

cid-is-not-rdns 

Severity: error

The component ID is required to follow a reverse domain-name scheme for its name. See the AppStream specification for details.

cid-desktopapp-is-not-rdns 

Severity: warning

The component ID is not a reverse domain-name. Please update the ID to avoid future issues and be compatible with all AppStream implementations. You may also consider to update the name of the accompanying .desktop file to follow the latest version of the Desktop-Entry specification and use a rDNS name for it as well. In any case, do not forget to mention the new desktop-entry in a <launchable/> tag for this component to keep the application launchable from software centers and the .desktop file data associated with the metainfo data.

cid-maybe-not-rdns 

Severity: info

The component ID might not follow the reverse domain-name schema (the TLD used by it is not known to the validator).

cid-invalid-character 

Severity: error

The component ID contains an invalid character. Only ASCII characters, dots and numbers are permitted.

cid-punctuation-prefix 

Severity: error

The component ID starts with punctuation. This is not allowed.

cid-rdns-contains-hyphen 

Severity: warning

The component ID contains a hyphen/minus in its domain part. Using a hyphen is strongly discouraged to improve interoperability with other tools such as D-Bus. A good option is to replace any hyphens with underscores (`_`). Hyphens are only allowed in the last segment of a component ID.

cid-has-number-prefix 

Severity: info

The component ID contains a segment starting with a number. Starting a segment of the reverse-DNS ID with a number is strongly discouraged, to keep interoperability with other tools such as D-Bus. Ideally, prefix these segments with an underscore.

cid-contains-uppercase-letter 

Severity: pedantic

The component ID should only contain lowercase characters.

cid-domain-not-lowercase 

Severity: error

The domain part of the rDNS component ID (first two parts) must only contain lowercase characters.

cid-missing-affiliation-freedesktop 

Severity: warning

The component is part of the Freedesktop project, but its ID does not start with fd.o's reverse-DNS name ("org.freedesktop").

cid-missing-affiliation-kde 

Severity: warning

The component is part of the KDE project, but its ID does not start with KDEs reverse-DNS name ("org.kde").

cid-missing-affiliation-gnome 

Severity: info

The component is part of the GNOME project, but its ID does not start with GNOMEs reverse-DNS name ("org.gnome").

spdx-expression-invalid 

Severity: error

The SPDX license expression is invalid and could not be parsed.

spdx-license-unknown 

Severity: warning

The license ID was not found in the SPDX database. Please check that the license ID is written in an SPDX-conformant way and is a valid free software license.

metadata-license-too-complex 

Severity: error

The metadata itself seems to be licensed under a complex collection of licenses. Please license the data under a simple permissive license, like FSFAP, MIT or CC0-1.0 to allow distributors to include it in mixed data collections without the risk of license violations due to mutually incompatible licenses.

metadata-license-invalid 

Severity: error

The metadata itself does not seem to be licensed under a permissive license. Please license the data under a permissive license, like FSFAP, CC0-1.0 or 0BSD to allow distributors to include it in mixed data collections without the risk of license violations due to mutually incompatible licenses.

update-contact-no-mail 

Severity: warning

The update-contact does not appear to be a valid email address (escaping of `@` is only allowed as `_at_` or `_AT_`).

screenshot-invalid-env-style 

Severity: warning

The `environment` property is set to an unrecognized graphical environment/style combination.

screenshot-invalid-width 

Severity: warning

The `width` property must be a positive integer.

screenshot-invalid-height 

Severity: warning

The `height` property must be a positive integer.

screenshot-invalid-scale 

Severity: warning

The `scale` property must be a positive integer.

screenshot-image-invalid-type 

Severity: error

The image type must be either `source` or `thumbnail`.

screenshot-image-missing-width 

Severity: warning

The `width` property must be present if the image type is `thumbnail`.

screenshot-image-missing-height 

Severity: warning

The `height` property must be present if the image type is `thumbnail`.

screenshot-image-source-duplicated 

Severity: error

There can only be one `source` image per screenshot and language.

screenshot-image-source-missing 

Severity: error

A screenshot must have at least one image of type `source`.

screenshot-image-not-found 

Severity: warning

Unable to reach the screenshot image on its remote location - does the image exist?

screenshot-video-not-found 

Severity: warning

Unable to reach the screenshot video on its remote location - does the video file exist?

screenshot-media-url-not-secure 

Severity: info

Consider using a secure (HTTPS) URL to reference this screenshot image or video.

screenshot-no-unscaled-image 

Severity: warning

A screenshot must have at least one image that has a scaling factor of 1.

screenshot-no-media 

Severity: error

A screenshot must contain at least one image or video in order to be useful. Please add an <image/> to it.

screenshot-mixed-images-videos 

Severity: error

A screenshot must contain either images or videos, but not both at the same time. Please use this screenshot exclusively for either static images or for videos.

screenshot-no-caption 

Severity: pedantic

The screenshot does not have a caption text. Consider adding one.

screenshot-video-codec-missing 

Severity: info

The screenshot video does not specify which video codec was used in a `codec` property.

screenshot-video-container-missing 

Severity: pedantic

The screenshot video does not specify which container format was used in a `container` property.

screenshot-video-codec-invalid 

Severity: warning

The selected video codec is not supported by AppStream and software centers may not be able to play the video. Only the AV1 and VP9 codecs are currently supported, using `av1` and `vp9` as values for the `codec` property.

screenshot-video-container-invalid 

Severity: warning

The selected video container format is not supported by AppStream and software centers may not be able to play the video. Only the WebM and Matroska video containers are currently supported, using `webm` and `mkv` as values for the `container` property.

screenshot-video-file-wrong-container 

Severity: warning

For videos, only the WebM and Matroska (.mkv) container formats are currently supported. The file extension of the referenced video does not belong to either of these formats.

screenshot-default-contains-video 

Severity: error

The default screenshot of a software component must not be a video. Use a static image as default screenshot and set the video as a secondary screenshot.

screenshot-default-missing 

Severity: warning

No screenshot is marked as default.

relation-invalid-tag 

Severity: warning

Found an unknown tag in a requires/recommends group. This is likely an error, because a component relation of this type is unknown.

relation-item-no-value 

Severity: error

A `requires` or `recommends` item requires a value to denote a valid relation.

relation-item-has-version 

Severity: warning

Found `version` property on required/recommended item of a type that should not have or require a version.

relation-item-missing-compare 

Severity: info

Found `version` property on this required/recommended item, but not `compare` property. It is recommended to explicitly define a comparison operation.

relation-item-invalid-vercmp 

Severity: error

Invalid comparison operation on relation item. Only one of `eq/ne/lt/gt/le/ge` is permitted.

relation-item-has-vercmp 

Severity: info

The relation item has a comparison operation set, but does not support any comparisons.

relation-item-redefined 

Severity: warning

This relation item has already been defined once for this or a different relation type. Please do not redefine relations.

relation-memory-in-requires 

Severity: info

Found a memory size relation in a `requires` tag. This means users will not be able to even install the component without having enough RAM. This is usually not intended and you want to use `memory` in the `recommends` tag instead.

relation-control-in-requires 

Severity: info

Found a user input control relation in a `requires` tag. This means users will not be able to even install the component without having the defined input control available on the system. This is usually not intended and you want to use `control` in the `recommends` tag instead.

relation-control-value-invalid 

Severity: warning

This `control` item defines an unknown input method and is invalid. Check the specification for a list of permitted values.

relation-display-length-value-invalid 

Severity: warning

This `display_length` item contains an invalid display length. Its value must be a positive integer value denoting logical pixels. Please refer to the AppStream specification for more information on this tag.

relation-display-length-side-property-invalid 

Severity: warning

This `side` property of this `display_length` item contains an invalid value. It must either be `shortest` or `longest`, or unset to imply `shortest` to make the item value refer to either the shortest or longest side of the display.

relation-hardware-value-invalid 

Severity: warning

This `hardware` item contains an invalid value. It should be a Computer Hardware ID (CHID) UUID without braces.

relation-memory-value-invalid 

Severity: warning

A `memory` item must only contain a non-zero integer value, depicting a system memory size in mebibyte (MiB)

relation-internet-value-invalid 

Severity: warning

The set tag value is not valid for an `internet` relation.

relation-internet-bandwidth-offline 

Severity: warning

The `bandwidth_mbitps` property is not allowed when using `offline-only` as value.

relation-internet-bandwidth-value-invalid 

Severity: warning

The value of this property must be a positive integer value, describing the minimum required bandwidth in mbit/s.

component-type-invalid 

Severity: error

The set component type is not a recognized, valid AppStream component type.

component-priority-in-metainfo 

Severity: warning

The component has a priority value set. This is not allowed in metainfo files.

component-merge-in-metainfo 

Severity: warning

The component has a `merge` method defined. This is not allowed in metainfo files.

component-id-missing 

Severity: error

The component is missing an ID (<id/> tag).

component-name-missing 

Severity: error

The component is missing a name (<name/> tag).

component-name-too-long 

Severity: warning

The name of this component is excessively long and can likely not be displayed properly in most layouts.

component-summary-missing 

Severity: error

The component is missing a summary (<summary/> tag).

id-tag-has-type 

Severity: info

The <id/> tag still contains a `type` property, probably from an old conversion to the recent metainfo format.

multiple-pkgname 

Severity: pedantic

The `pkgname` tag appears multiple times. You should evaluate creating a metapackage containing the metainfo and .desktop files in order to avoid defining multiple package names per component.

name-has-dot-suffix 

Severity: pedantic

The component name should (likely) not end with a dot (`.`).

summary-has-dot-suffix 

Severity: info

The component summary should not end with a dot (`.`).

summary-has-tabs-or-linebreaks 

Severity: error

The component summary must not contain tabs or linebreaks.

summary-has-url 

Severity: error

The summary must not contain any URL. Use the `<url/>` tags for links.

summary-first-word-not-capitalized 

Severity: info

The summary text does not start with a capitalized word, project name or number.

summary-too-long 

Severity: warning

The summary text is very long, and will likely not be displayed properly everywhere.

icon-stock-cached-has-url 

Severity: error

Icons of type `stock` or `cached` must not contain an URL, a full or an relative path to the icon. Only file basenames or stock names are allowed.

icon-remote-no-url 

Severity: error

Icons of type `remote` must contain an URL to the referenced icon.

icon-remote-not-found 

Severity: warning

Unable to reach remote icon at the given web location - does it exist?

icon-remote-not-secure 

Severity: info

Consider using a secure (HTTPS) URL for the remote icon link.

metainfo-invalid-icon-type 

Severity: error

Metainfo files may only contain icons of type `stock` or `remote`, the set type is not allowed.

url-invalid-type 

Severity: warning

Invalid `type` property for this `url` tag. URLs of this type are not known in the AppStream specification.

url-not-reachable 

Severity: warning

Unable to reach remote location that this URL references - does it exist?

url-not-secure 

Severity: info

Consider using a secure (HTTPS) URL for this web link.

web-url-expected 

Severity: error

A web URL was expected for this value.

url-uses-ftp 

Severity: warning

This web link uses the FTP protocol. Consider switching to HTTP(S) instead.

url-redefined 

Severity: warning

An URL of this type has already been defined.

developer-name-tag-deprecated 

Severity: info

The toplevel `developer_name` element is deprecated. Please use the `name` element in a `developer` block instead.

developer-name-has-url 

Severity: warning

The `name` child of a `developer` block must not contain a hyperlink.

developer-id-missing 

Severity: info

The `developer` element is missing an `id` property, containing a unique string ID for the developer. Consider adding a unique ID.

unknown-desktop-id 

Severity: error

The set value is not an identifier for a desktop environment as registered with Freedesktop.org.

launchable-unknown-type 

Severity: error

This `launchable` tag has an unknown type and can not be used.

bundle-unknown-type 

Severity: error

This `bundle` tag has an unknown type and can not be used.

update-contact-in-catalog-data 

Severity: warning

The `update_contact` tag should not be included in catalog AppStream XML.

nonstandard-gnome-extension 

Severity: info

This tag is a GNOME-specific extension to AppStream and not part of the official specification. Do not expect it to work in all implementations and in all software centers.

unknown-tag 

Severity: info

Found invalid tag. Non-standard tags should be prefixed with `x-`. AppStream also provides the <custom/> tag to add arbitrary custom data to metainfo files. This tag is read by AppStream libraries and may be useful instead of defining new custom toplevel or `x-`-prefixed tags if you just want to add custom data to a metainfo file.

metadata-license-missing 

Severity: error

The essential tag `metadata_license` is missing. A license for the metadata itself always has to be defined.

app-description-required 

Severity: error

The component is missing a long description. Components of this type must have a long description.

font-description-missing 

Severity: info

It would be useful to add a long description to this font to present it better to users.

driver-firmware-description-missing 

Severity: info

It is recommended to add a long description to this component to present it better to users.

generic-description-missing 

Severity: pedantic

This generic component is missing a long description. It may be useful to add one.

desktop-app-launchable-missing 

Severity: error

This `desktop-application` component is missing a `desktop-id` launchable tag. This means that this application can not be launched and has no association with its desktop-entry file. It also means no icon data or category information from the desktop-entry file will be available, which will result in this application being ignored entirely.

desktop-app-launchable-omitted 

Severity: info

This `desktop-application` component has no `desktop-id` launchable tag, however it contains all the necessary information to display the application. The omission of the launchable entry means that this application can not be launched directly from installers or software centers. If this is intended, this information can be ignored, otherwise it is strongly recommended to add a launchable tag as well.

console-app-no-binary 

Severity: warning

Type `console-application` component, but no information about binaries in $PATH was provided via a `provides/binary` tag.

web-app-no-url-launchable 

Severity: error

This `web-application` component is missing a `launchable` tag of type `url`.

web-app-no-icon 

Severity: error

This `web-application` component is missing a `icon` tag to specify a valid icon.

web-app-no-category 

Severity: warning

This `web-application` component is missing categorizations. A `categories` block is likely missing.

font-no-font-data 

Severity: error

Type `font` component, but no font information was provided via a `provides/font` tag.

driver-no-modalias 

Severity: warning

Type `driver` component, but no modalias information was provided via a `provides/modalias` tag.

extends-not-allowed 

Severity: error

An `extends` tag is specified, but the component is not of type `addon`, `localization` or `repository`.

addon-extends-missing 

Severity: error

The component is an addon, but no `extends` tag was specified.

localization-extends-missing 

Severity: info

This `localization` component is missing an `extends` tag, to specify the components it adds localization to.

localization-no-languages 

Severity: error

This `localization` component does not define any languages this localization is for.

service-no-service-launchable 

Severity: error

This `service` component is missing a `launchable` tag of type `service`.

metainfo-suggestion-type-invalid 

Severity: warning

Suggestions of any type other than `upstream` are not allowed in metainfo files.

category-invalid 

Severity: warning

The category name is not valid. Refer to the XDG Menu Specification for a list of valid category names.

all-categories-ignored 

Severity: warning

All categories for this component have been ignored, either because they were invalid or because they are of low quality (e.g. custom 'X-' prefixed or toolkit ones like 'GTK' or 'Qt'). Please fix your category names, or add more categories.

app-categories-missing 

Severity: error

This component is in no valid categories, even though it should be. Please check its metainfo file and desktop-entry file.

screenshot-caption-too-long 

Severity: info

The screenshot caption is too long (should be <= 100 characters)

file-read-failed 

Severity: error

Unable to read file.

xml-markup-invalid 

Severity: error

The XML of this file is malformed.

component-catalog-tag-invalid 

Severity: error

Invalid tag found in catalog metadata. Only `component` tags are permitted.

metainfo-ancient 

Severity: error

The metainfo file uses an ancient version of the AppStream specification, which can not be validated. Please migrate it to version 0.6 (or higher). Modern files use the `component` root tag and include many other differences, so check for changes carefully when modernizing the data.

root-tag-unknown 

Severity: error

This XML document has an unknown root tag. Maybe this file is not a metainfo document?

metainfo-filename-cid-mismatch 

Severity: warning

The metainfo filename does not match the component ID.

desktop-file-load-failed 

Severity: error

Unable to load the desktop-entry file associated with this component.

desktop-file-not-found 

Severity: warning

This component metadata refers to a non-existing .desktop file.

desktop-entry-category-invalid 

Severity: warning

A category defined in the desktop-entry file is not valid. Refer to the XDG Menu Specification for a list of valid categories.

desktop-entry-bad-data 

Severity: warning

Error while reading some data from the desktop-entry file.

desktop-entry-value-invalid-chars 

Severity: warning

The value of this desktop-entry field contains invalid or non-printable UTF-8 characters, which can not be displayed properly.

desktop-entry-value-quoted 

Severity: warning

This desktop-entry field value is quoted, which is likely unintentional.

desktop-entry-hidden-set 

Severity: warning

This desktop-entry file has the 'Hidden' property set. This is wrong for vendor-installed .desktop files, and nullifies all effects this .desktop file has (including MIME associations), which most certainly is not intentional.

desktop-entry-empty-onlyshowin 

Severity: warning

This desktop-entry file has the 'OnlyShowIn' property set with an empty value. This might not be intended, as this will hide the application from all desktops. If you do want to hide the application from all desktops, using 'NoDisplay=true' is more explicit.

dir-no-metadata-found 

Severity: info

No AppStream metadata was found in this directory or directory tree.

dir-applications-not-found 

Severity: pedantic

No XDG applications directory found.

metainfo-legacy-path 

Severity: warning

The metainfo file is stored in a legacy path. Please place it in `/usr/share/metainfo/`.

metainfo-multiple-components 

Severity: warning

The metainfo file specifies multiple components. This is not allowed.

releases-not-in-order 

Severity: warning

The releases are not sorted in a latest to oldest version order. This is required as some tools will assume that the latest version is always at the top. Sorting releases also increases overall readability of the metainfo file.

releases-type-invalid 

Severity: error

The type of the releases block is invalid. It needs to either `embedded` (the default) or `external`.

releases-url-insecure 

Severity: error

The URL to an external release metadata file is insecure. This is not allowed, please use HTTPS URLs only.

releases-download-failed 

Severity: error

Failed to download release metadata.

releases-external-not-found 

Severity: warning

A local release metadata file was not found. It is strongly recommended to validate this metadata together with the main MetaInfo file.

release-urgency-invalid 

Severity: warning

The value set as release urgency is not a known urgency value.

release-type-invalid 

Severity: warning

The value set as release type is invalid.

release-version-missing 

Severity: error

The release is missing the `version` property.

release-time-missing 

Severity: error

The release is missing either the `date` (preferred) or the `timestamp` property.

release-timestamp-invalid 

Severity: error

The release timestamp is invalid.

release-description-outside-tag 

Severity: error

The release description must be put inside a `description` tag

artifact-type-invalid 

Severity: error

The value set as artifact type is invalid. Must be either `source` or `binary`.

artifact-bundle-type-invalid 

Severity: warning

The value set as artifact bundle type is invalid.

artifact-invalid-platform-triplet 

Severity: warning

The platform triplet for this release is invalid. It must be in the form of `architecture-oskernel-osenv` - refer to the AppStream documentation or information on normalized GNU triplets for more information and valid fields.

artifact-checksum-type-invalid 

Severity: error

The selected checksumming algorithm is unsupported or unknown.

artifact-size-type-invalid 

Severity: error

The size type is unknown. Must be `download` or `installed`.

artifact-filename-not-basename 

Severity: error

The artifact filename must be a file basename, not a (relative or absolute) path.

release-issue-type-invalid 

Severity: error

The value set as release issue type is invalid.

release-issue-is-cve-but-no-cve-id 

Severity: warning

The issue is tagged at security vulnerability with a CVE number, but its value does not look like a valid CVE identifier.

releases-info-missing 

Severity: pedantic

This component is missing information about releases. Consider adding a `releases` tag to describe releases and their changes.

invalid-iso8601-date 

Severity: warning

The AppStream specification requires a complete, ISO 8601 date string with at least day-granularity to denote dates. Please ensure the date string is valid.

circular-component-relation 

Severity: warning

This component extends, provides, requires or recommends itself, which is certainly not intended and may confuse users or machines dealing with this metadata.

runtime-project-license-no-ref 

Severity: info

Licenses for `runtime` components are usually too complex to reflect them in a simple SPDX expression. Consider using a `LicenseRef` and a web URL as value for this component's `project_license`. E.g. `LicenseRef-free=https://example.com/licenses.html`

runtime-no-provides 

Severity: pedantic

Since a `runtime` component is comprised of multiple other software components, their component-IDs may be listed in a `<provides/>` section for this runtime.

unknown-provides-item-type 

Severity: info

The type of the item that the component provides is not known to AppStream.

mimetypes-tag-deprecated 

Severity: warning

The toplevel `mimetypes` tag is deprecated. Please use `mediatype` tags in a `provides` block instead to indicate that your software provides a media handler for the given types.

content-rating-missing 

Severity: info

This component has no `content_rating` tag to provide age rating information. You can generate the tag data online by answering a few questions at https://hughsie.github.io/oars/

content-rating-type-missing 

Severity: error

The `type` attribute of this `content_rating` element is missing or empty.

content-rating-type-invalid 

Severity: error

The `type` attribute of the `content_rating` element has a invalid value.

content-rating-invalid-tag 

Severity: error

The `content_rating` tag can only contain `content_attribute` children.

content-attribute-id-missing 

Severity: error

The `id` attribute of the `content_attribute` element is missing or empty.

content-attribute-id-invalid 

Severity: error

The `id` attribute of the `content_attribute` element has a invalid value.

content-attribute-value-empty 

Severity: error

The `content_attribute` tag needs a value.

content-attribute-value-unknown 

Severity: error

The `content_attribute` tag value is unknown.

content-attribute-value-invalid 

Severity: error

The `content_attribute` tag value is invalid for the given id.

content-attribute-id-duplicated 

Severity: error

A `content_attribute` tag with this ID has already been defined.

usertag-missing-namespace 

Severity: info

This `tag` is missing a `namespace` attribute.

usertag-invalid 

Severity: error

This tag or its namespace contains invalid characters. Only lower-cased ASCII letters, numbers, dots, hyphens and underscores are permitted.

branding-color-type-invalid 

Severity: error

The type of this color is not valid.

branding-color-scheme-type-invalid 

Severity: error

The value of this color scheme preference is not valid.

branding-color-invalid 

Severity: error

This color is not a valid HTML color code.

reference-doi-invalid 

Severity: warning

The given DOI (Digital Object Identifier) for this reference item is not valid.

reference-citation-url-invalid 

Severity: warning

The value for this citation reference item must be an URL to a CFF (Citation File Format) file.

reference-registry-name-missing 

Severity: error

This registry reference item is missing the `name` property to denote the name of the registry it is about.

reference-registry-name-unknown 

Severity: warning

The registry for this reference item is unknown. This may be due to a typing error, or the registry needs to be registered with AppStream.

reference-value-missing 

Severity: error

The reference item is missing a value.

custom-invalid-tag 

Severity: error

The `custom` tag can only contain `value` children.

custom-key-missing 

Severity: error

This `custom` tag value is missing a `key` attribute.

custom-key-duplicated 

Severity: error

A key can only be used once.

custom-value-empty 

Severity: info

This custom value is empty.

metainfo-localized-keywords-tag 

Severity: error

A `keywords` tag must not be localized in metainfo files (upstream metadata). Localize the individual keyword entries instead.