Timing Entry Names Registry

Status of this document

This is a public copy of the editors’ draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don’t cite this document other than as work in progress.

GitHub Issues are preferred for discussion of this specification.

This document is governed by the 18 August 2025 W3C Process Document.

For updates, see Registration Entry Requirements and Update Process.

1. Purpose

Performance Timeline [PERFORMANCE-TIMELINE-2] defines primitives that enable web developers to access, instrument, and retrieve various performance metrics from the full lifecycle of a web application. The performance data of various metrics is hosted in PerformanceEntry objects. The type of interface for a PerformanceEntry object is identified with entryType.

This registry is intended to provide a central location for enumerating identified interface types of PerformanceEntry object.

2. Registration Entry Requirements and Update Process

Each entry type must include a unique identifier used by entryType, where the scope of uniqueness is the entryType itself.
Each entry type should include a link that references a public available specification (PAS) that defines the associated interface type.
Each entry type must include contact information of the requestor.
Each entry type must include an availableFromTimeline boolean indicating whether this entry type is available from the Performance interface.
Each entry type must include a maxBufferSize indicating the maximum buffer size for this entry type.
Each entry type must specify an algorithm should add entry which, given a PerformanceEntry entry of the entry type and optionally a PerformanceObserverInit options of an observer observing that entry type, determines the following:
1. If options was not provided, whether entry is eligible to be added to the performance timeline, regardless of limitations in the buffer size.
2. Otherwise, given registered performance observer regObs containing options in its options list, whether entry must be appended to regObs’s observer’s observer buffer.

An update to this registry is one of the following:

An addition or deprecation of an identifier. Removal of identifiers is strongly discouraged.
An addition, change, or removal of a column to the table. The column containing identifiers must not be removed or changed.

Any person can request an update to this registry by pull requests to the timing-entrytypes-registry repository. The Web Performance Working Group will place it on an upcoming meeting agenda and notify the requestor. Consideration and disposition of the request is by consensus of the W3C Web Performance Working Group. The Chair will then notify the requestor of the outcome and update the registry accordingly.

3. Registry

This section is the registry of identified entryType values for performance timeline interfaces [PERFORMANCE-TIMELINE-2].

`entryType` Identifier	Interface Type(s)	availableFromTimeline	maxBufferSize	should add entry	Public Specification(s)	Requestor Contact
`"container"`	`PerformanceContainerTiming`	`False`	`150`	Return true	[CONTAINER-TIMING]	WICG
`"element"`	`PerformanceElementTiming`	`False`	`150`	Return true	[ELEMENT-TIMING]	WICG
`"event"`	`PerformanceEventTiming`	`False`	`150`	Should add PerformanceEventTiming	[EVENT-TIMING]	W3C
`"first-input"`	`PerformanceEventTiming`	`True`	`1`	Should add PerformanceEventTiming	[EVENT-TIMING]	W3C
`"largest-contentful-paint"`	`LargestContentfulPaint`	`False`	`150`	Return true	[LARGEST-CONTENTFUL-PAINT]	W3C
`"layout-shift"`	`LayoutShift`	`False`	`150`	Return true	[LAYOUT-INSTABILITY]	WICG
`"longtask"`	`PerformanceLongTaskTiming`	`False`	`200`	Return true	[LONGTASKS-1]	W3C
`"long-animation-frame"`	`PerformanceLongAnimationFrameTiming`	`True`	`200`	Return true	[LONG-ANIMATION-FRAMES]	W3C
`"mark"`	`PerformanceMark`	`True`	`Infinite`	Return true	[USER-TIMING-2]	W3C
`"measure"`	`PerformanceMeasure`	`True`	`Infinite`	Return true	[USER-TIMING-2]	W3C
`"navigation"`	`PerformanceNavigationTiming`	`True`	`Infinite`	Return true	[NAVIGATION-TIMING-2]	W3C
`"paint"`	`PerformancePaintTiming`	`True`	`2`	Return true	[PAINT-TIMING]	W3C
`"resource"`	`PerformanceResourceTiming`	`True`	`250`	Return true	[RESOURCE-TIMING-2]	W3C
`"visibility-state"`	`VisibilityStateEntry`	`True`	`50`	Return true	[HTML]	HTML

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Conformant Algorithms

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Conformance requirements phrased as algorithms or specific steps can be implemented in any manner, so long as the end result is equivalent. In particular, the algorithms defined in this specification are intended to be easy to understand and are not intended to be performant. Implementers are encouraged to optimize.

Index

Terms defined by this specification

Terms defined by reference

[CONTAINER-TIMING] defines the following terms:

PerformanceContainerTiming

[ELEMENT-TIMING] defines the following terms:

PerformanceElementTiming

[EVENT-TIMING] defines the following terms:

PerformanceEventTiming
should add PerformanceEventTiming

[HR-TIME-3] defines the following terms:

Performance

[HTML] defines the following terms:

VisibilityStateEntry

[LARGEST-CONTENTFUL-PAINT] defines the following terms:

LargestContentfulPaint

[LAYOUT-INSTABILITY] defines the following terms:

LayoutShift

[LONG-ANIMATION-FRAMES] defines the following terms:

PerformanceLongAnimationFrameTiming

[LONGTASKS-1] defines the following terms:

PerformanceLongTaskTiming

[NAVIGATION-TIMING-2] defines the following terms:

PerformanceNavigationTiming

[PAINT-TIMING] defines the following terms:

PerformancePaintTiming

[PERFORMANCE-TIMELINE-2] defines the following terms:

PerformanceEntry
PerformanceObserverInit
entryType
observer
observer buffer
options list
registered performance observer

[RESOURCE-TIMING-2] defines the following terms:

PerformanceResourceTiming

[USER-TIMING] defines the following terms:

PerformanceMark
PerformanceMeasure