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The reference image for Acid3.
Type of site Web standards test
Available language(s) English language
Owner The Web Standards Project
Created by Ian Hickson
Launched 3 March 2008

Acid3 is a test page from the Web Standards Project that checks how well a web browser follows certain web standards, especially relating to the Document Object Model and JavaScript.

When successful, the Acid3 test displays a gradually increasing percentage counter with colored rectangles in the background. The percentage displayed is based on the number of subtests passed. It is not representing an actual percentage of conformance as the test does not keep track of how many of the subtests were actually started (100 is assumed). In addition to these the browser also has to render the page exactly like the reference page is rendered in the same browser. Like the text of the Acid2 test, the text of the reference rendering is not a bitmap, in order to allow for certain differences in font rendering.

Acid3 was in development from April 2007,[1] and released on 3 March 2008.[2] The main developer was Ian Hickson, who also wrote the Acid2 test. Acid2 focused primarily on Cascading Style Sheets, but this third Acid test focuses also on technologies used on modern, highly interactive websites characteristic of Web 2.0, such as ECMAScript and DOM Level 2. A few subtests also concern Scalable Vector Graphics (SVG), XML, and data URIs. It includes several elements from W3C CSS3 working drafts that have not made it to candidate recommendations yet.


[edit] The test

The main part of Acid3 is written in ECMAScript (JavaScript) and consists of 100 subtests in six groups called "buckets", including four special subtests (0, 97, 98, and 99).[3]

  • Bucket 1: DOM Traversal, DOM Range, HTTP
  • Bucket 2: DOM2 Core and DOM2 Events
  • Bucket 3: DOM2 Views, DOM2 Style, CSS 3 selectors and Media Queries
  • Bucket 4: Behavior of HTML tables and forms when manipulated by script and DOM2 HTML
  • Bucket 5: Tests from the Acid3 Competition (SVG,[4] HTML, SMIL, Unicode, ...)
  • Bucket 6: ECMAScript

The compliance criteria requires that the test is run with a browser's default settings. The final rendering must have a 100/100 score and must not only be pixel-identical with the reference rendering, including the favicon (or more accurately, its desired absence; a favicon is not supposed to show up in a 100/100 render), but the animation has to be smooth (taking no more than 33 ms for each subtest on the top-of-the-line Apple laptop) as well.[5]

Acid3 rendered by Fennec 1.0 alpha 1. Buckets 2, 4, and 6 pass all 16 subtests, buckets 1 and 3 pass more than 10 subtests while bucket 5 passes more than 5 subtests.

As the test is run, rectangles are added to the rendered image; the color of the rectangles is decided by the number of subtests passed in the bucket. If all subtests fail in a particular bucket, its associated rendered rectangle will be invisible. If some subtests are cleared the color will change in four steps:

  • 1-5 subtests passed: Black rectangle.
  • 6-10 subtests passed: Grey rectangle.
  • 11-15 subtests passed: Silver rectangle.
  • All 16 subtests passed: Colored rectangle (red, orange, yellow, lime, blue, purple — for each of the six rectangles, respectively).

After the Acid3 test page is completely rendered, the capital A in the word Acid3 can be clicked to see an alert (or Shift-Click for a new window) explaining exactly which subtests have failed, and what the error message was.

In order to render the test correctly, user agents need to implement the CSS 3 Text Shadows and the CSS 2.x Downloadable Fonts specifications, which are currently under consideration by W3C to be standardized. This is required as the test uses a custom TrueType font, called "AcidAhemTest" to cover up an "X" on fuchsia colored background. The glyph, when rendered by the downloaded font, is just a square, made white with CSS, and thus invisible.[citation needed]

In addition, the test also uses Base64 encoded images, some more advanced selectors, CSS 3 color values (HSLA) as well as bogus selectors and values that should be ignored.

[edit] Development and impact

Ian Hickson started working on the test in April 2007, but development progressed slowly. In December 2007, work restarted and the project received public attention on 10 January 2008, when it was mentioned in blogs by Anne van Kesteren[6] and Dustin Brewer.[7] At the time the project resided at a URL clearly showing its experimental nature: "" That did not stop the test from receiving widespread attention within the web development community. At that time only 84 subtests were done, and on 14 January Ian Hickson announced a competition to develop the missing 16.[8]

The following developers contributed to the final test through this competition:

  • Sylvain Pasche. Subtest 66–67 (DOM).
  • David Chan. Subtest 68 (UTF-16/UCS-2).
  • Simon Pieters (Opera) and Anne van Kesteren (Opera). Subtest 71: HTML parsing.
  • Jonas Sicking (Mozilla) and Garrett Smith. Subtest 72: dynamic modification of style blocks' text nodes.
  • Jonas Sicking (Mozilla). Subtest 73: Nested events.
  • Erik Dahlström (Opera). Subtest 74–78: SVG and SMIL.
  • Cameron McCormack (Batik SVG library). Subtest 79: SVG fonts.

Even before its official release, Acid3's impact on browser development was dramatic. WebKit in particular made progress; in less than a month their score rose from 60 to 87.[9]

The test was officially released on 3 March 2008.[2] A guide and commentary was expected to follow within a few months[9], however, as of September 2008 it has not yet been released. The announcement that the test is complete means only that it is to be considered "stable enough" for actual use; if problems and bugs are found, it will still be modified to fix it. The test has already been modified to fix several issues including issues relating to sub-pixel positioning, SVG surrogate pairs and performance.[10] On 26 March 2008—the day both Opera and WebKit teams announced a 100/100 score—developers of WebKit contacted main Acid3 developer Ian Hickson about a critical bug in the Acid3 that presumably may have forced a violation of the SVG 1.1 standard to pass; thus Hickson proceeded to fix it with the help of Cameron McCormack, member of W3C's SVG Working Group.[11][12]

By the end of March 2008, early development versions of the Presto and WebKit layout engines scored 100/100 on the test and rendered the test page correctly.[13][12][14] Presto still has performance issues in producing a smooth animation in the test, thus it has not passed the Acid3 test yet. As of build r36882, WebKit produces a smooth animation on the reference hardware, and thus passes the Acid3 test.[15] Firefox developers had been preparing for the imminent release of Firefox 3, as a result they had focused on stability rather than passing the Acid3 test.[16] Microsoft, developers of the Internet Explorer browser, said that Acid3 does not map to the goal of Internet Explorer 8 and that IE8 will improve only some of the standards being tested by Acid3.[17]

On 22 April 2008, Hickson again fixed a bug in the Acid3 test discovered by a Mozilla developer. This change possibly invalidates the previously reported scores of 100/100 for development versions of Presto and WebKit.[18] On 29 September 2008, David Baron raised an issue with the CSS Working Group concerning media queries that might cause the test to change again.[19]

[edit] Standards tested

The following standards are tested by Acid3:

  • DOM Level 2 Traversal (subtests 1-6)
  • DOM Level 2 Range (subtests 7-11)
  • Content-Type: image/png; text/plain (subtest 14, 15)
  • <object> handling and HTTP status codes (subtest 16)
  • DOM Level 2 Core (subtests 17, 21)
  • DOM Level 2 Events (subtests 17, 30-32)
  • CSS Selectors (subtests 33-40)
  • DOM Level 2 Style (subtest 45)
  • DOM Level 2 HTML (subtest 60)
  • DOM Level 2 Views
  • ECMAScript GC (subtests 26-27)
  • Unicode 5.0 UTF-16 (subtest 68)
  • Unicode 5.0 UTF-8 (subtest 70)
  • HTML 4.0 Transitional (subtest 71)
  • HTML 4.01 Strict
  • SVG 1.1 (subtests 74, 78)
  • SVG 1.1 Fonts (subtests 77, 79)
  • SMIL 2.1 (subtests 75-76)
  • ECMAScript Conformance (subtests 81-96)
  • Data URI scheme (subtest 97)
  • XHTML 1.0 Strict (subtest 98)
  • HTTP 1.1 Protocol

[edit] Passing conditions

A passing score is only considered valid if the browser's default settings were used.

The following browser settings and user actions invalidate the test:

  • Zooming in or out
  • Disabling images
  • Applying custom fonts, colors, styles, etc.

Also User JavaScript or Greasemonkey scripts may invalidate the test.

[edit] Layout engines

Acid3 was deliberately written in such a way that every web browser failed the test at the time of its release. Many of the browser teams are actively working to improve test results.

[edit] Desktop browsers

Desktop layout engine progress for the Acid3 test
Layout Engine Major Browsers Screen­shot of Latest Release at Time of Acid3 Release Screen­shot of Current Release Screen­shot of Preview Release
Gecko Firefox




Firefox 3.0.8


Firefox 3.6a1pre


KHTML Konqueror


Konqueror 4.0.2


Konqueror 4.2.1


Konqueror snapshot 4.2.67 (r940805)


Presto Opera


Opera 9.27


Opera 9.64


Opera 10.0 Alpha 1

Trident Internet Explorer


IE 7.0


IE 8.0


WebKit Safari, Chrome


Safari 3.0.4


Safari 3.2.2


Google Chrome 1.0


Safari 4 Beta

100/100 (Failed)

Google Chrome

[edit] Mobile browsers

Mobile layout engine progress for the Acid3 test
Layout Engine Major Browsers Screen­shot of Latest Release at Time of Acid3 Release Screen­shot of Current Release Screen­shot of Preview Release Not­es
Gecko Fennec


Fennec 1.0 Beta 1


This is a misleading result as this isn't the score achieved on a mobile device. The last reported score on a Windows Mobile device with a fennec build was an 88/100.

Presto in Opera Mini Opera Mini


Opera Mini

Version 4.2.13337 (20081205) would produce results ranging from 4/100 to 98/100 possibly due to pre-processing.
Presto Opera Mobile


Opera Mobile 8.65


Opera Mobile 8.65


Opera Mobile 9.5 Beta

NetFront NetFront


NetFront 3.5

The latest version of NetFront 2.81 on the PlayStation 3 would produce 26/100.
S60 Webkit Nokia Mini Map Browser


S60 5th Edition

WebKit Mobile­Safari, Android Browser


iPhone firmware 1.1.4


iPhone firmware 2.2.1


Android RC33


Iris Browser 1.1.4


iPhone firmware 3.0 Beta

Switching between landscape and portrait during or after the test in Android will move the red square.

[edit] See also

[edit] References

  1. ^ "HTML5 IRC logs: freenode / #whatwg / 20070422". Retrieved on 2007-12-28. 
  2. ^ a b "Acid3: Putting Browser Makers on Notice, Again. (WaSP Press Release)". Retrieved on 2007-03-04. 
  3. ^ Hickson, Ian. "Comments in the source code of the test page". Retrieved on 2008-02-16. 
  4. ^ Dahlström, Erik (2008-01-22). "Getting to the core of the web". Retrieved on 2008-02-16. 
  5. ^ Ian Hickson (2008-04-01). "The performance aspect of Acid3". Retrieved on 2008-04-03. 
  6. ^ van Kesteren, Anne (2008-01-10). "Acid3". Retrieved on 2008-03-04. 
  7. ^ Brewer, Dustin (2008-01-10). "Developers are working on ACID3 test". Retrieved on 2008-03-04. 
  8. ^ Hickson, Ian (2008-01-14). "The competition for you to come up with the best test for Acid3". Retrieved on 2008-03-04. 
  9. ^ a b Hickson, Ian (2008-03-04). "Moebius (announcement of the completion of the test)". Retrieved on 2008-03-04. 
  10. ^ Ian Hickson. "Tests that are never quite finished". Retrieved on 2008-03-30. 
  11. ^ Ian Hickson. "Last minute changes to Acid3". Retrieved on 2008-03-30. 
  12. ^ a b Maciej Stachowiak (2008-03-26). "WebKit achieves Acid3 100/100 in public build". Retrieved on 2008-03-26. 
  13. ^ Junyor (March 2008). "Opera and the Acid3 Test". Retrieved on 2008-03-28. 
  14. ^ Lars Erik Bolstad (March 2008). "Public Acid3 build". Retrieved on 2008-03-28. "The latest post-9.5 build scores 99/100 and fails the smoothness criterion." 
  15. ^ "The latest WebKit development build scores 100/100, renders the test correctly, and passes the smoothness criterion". 
  16. ^ Mike Shaver (2008-03-27). "The missed opportunity of acid 3". Retrieved on 2008-03-30. 
  17. ^ Chris Wilson. "Windows Internet Explorer 8 Expert Zone Chat (20 March 2008)". Retrieved on 2008-04-15. "The ACID3 test is a collection of interesting tests, spread across a large set of standards. Some of those standards will see improvements in IE8 - in fact, IE8 already improves on IE7's score — but we are focused on the most important features and standards to make web developers' lives easier. The ACID3 test does not map directly to that goal." 
  18. ^ Ian Hickson (2008-04-22). "Media queries and performance in Acid3 (and an error on my part)". Retrieved on 2008-04-24. 
  19. ^ David Baron (2008-09-29). "should comma be an error handling recovery point?". Retrieved on 2008-09-29. 
  20. ^ "Bug 410460 (acid3) – Acid3 tracking bug". Retrieved on 2008-02-16. 
  21. ^ "Public Mozilla Acid3 spreadsheet". Retrieved on 2008-10-18. 
  22. ^ "Bug 156947: Konqueror 4 fails Acid3 test (Filed on 30 Jan. 2008)". Retrieved on 2008-03-02. 
  23. ^ "Index of /pub/". Retrieved on 2009-03-19. 
  24. ^ "Blog entry of Fennec Developer Brad Lassey". Retrieved on 2008-10-11. 
  25. ^ "MacRumors forum post". Retrieved on 2009-03-20. 

[edit] External links

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