Web Accessibility Made Easy

U.S. Government Website Accessibility Guidelines

NASA Insignia


This document was assembled by and with the help of NASA webmasters to assist NASA and other Federal webmasters in the goal of making all Government websites accessible to persons with disabilities. The information below represents source material and the actual guidelines with descriptions of intent and suggested methods of compliance. In addition to the guidelines, information on specific assistive technology developments and how they are used is found here on the Assistive Technology page.

NASA Webmasters are sharing their learned experience in making the multiple NASA web pages accessible. To see these best practices, including a fairly straightforward and easy to follow step-by-step approach to website accessibility assessment and cleanup, go to the NASA Webmasters Web Accessibility Best Practices  page.

For information on the renovation of NASA Headquarters web pages, check the schedule.

*Notice:  All links spawn new browser windows.

Architectural Compliance Board, Department of Justice, General Services Administration, and
World Wide Web Consortia Base Documents and Reference Materials

NASA Accessibility Guideline Checklist and Explanations


Web Practice

Accessibility Standard
Links go to tag reference at W3C.

Links go to more information and examples at CAST or W3C.


Text equivalent

A text equivalent for every non-text element shall be provided (e.g., via <alt>, <longdesc>, or in element content). 

The <alt> text tag provides a title or descriptive phrase about the image it accompanies. This is essential for users of reader software who are vision impaired and it is valuable for users of graphical browsers who have "load images" turned off. It is also useful for users of text-only WWW tools like Lynx. The <longdesc> tag can be essential when an image conveys important information such as what about the image represents a discovery if the image is a science result image.

Equivalent alternatives

Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation.

This states that any dynamic changes which occur based on multimedia content (either in a <frame>, <img>, <object>, or <script>) must also update the "alt" element when it changes.

Web page design

Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup. Good primer on Color Blindness  Link used with author's permission.

Thirty percent of all males suffer from some form of color deficiency rendering colors as grays or spreading one color across several others.   Choose text and background colors to provide maximum contrast.   Contrast is also very important for individuals who can see but have reduced vision. Good design also refers to the ability of reader software to properly parse a page correctly left to right and up to down.


Documents shall be organized so they are readable without requiring an associated style sheet.

Style sheets present a double-edged sword: Only the latest browsers support the specification and when using them the text still needs to be able to be parsed correctly by reader software.

Server-side image maps

Redundant text links shall be provided for each active region.

Most sites have moved away from server-side image maps.   The exception is for such things as geographical information system clickable maps.

Client-side image maps

Client-side image maps shall be provided instead of server-side images maps except where the regions cannot be defined with an available geometric shape.

Modern browsers support client-side image maps, with the addition of <alt> text tags for the image hot spots, assistive technology readers can provide additional clues.  However, if the user has "load images" turned off, the only approach is to provide alternative links elsewhere on the same page.

Data tables

Row and column headers shall be identified for data tables.

Using row and column headers becomes crucial when a table is larger than two columns or two rows.  Without the headers, assistive technology such as reader software can only recite the table contents with no reference to what that column or row pertains to.  See below.

Multi-logic row or column headers

Markup shall be used to associate data cells and header cells for data tables that have two or more logical levels of row or column headers.

Additional information such as <summary> and <scope> can be applied to data tables to render their contents and intent meaningful to users of assistive technology.  <Scope>, in particular, can be very useful for column headers.  See above.


Frames shall be titled with text that facilitates frame identification and navigation.

Frames present unique obstacles to users of reader software.  A frame-based page should always include an alternative layout (text only) inside a <noframe> element.  Also, with the <title>, <name> and <longdesc> tags, frames can be made more navigable for reader software.

Web page design

Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz.

Flicker and continuous motion (as from applets or javascripts or from refreshes) can cause seizures in individuals with photosensitive epilepsy.  Content developers should refrain from an overuse of time-sequenced elements. If used, the timing should be longer than half-a-second.

Organization & equivalent alternatives

A text-only page, with equivalent information or functionality, shall be provided to make a web site comply with the provisions of this part, when compliance cannot be accomplished in any other way. The content of the text-only page shall be updated whenever the primary page changes.

Content developers should only resort to alternative pages when other solutions fail.  An out-of-date page may be as frustrating as one that is inaccessible since, in both cases, the information presented on the original page is unavailable.  Before resorting to an alternative page, reconsider the design of the original page

Scripting languages

When pages utilize scripting languages to display content, or to create interface elements, the information provided by the script shall be identified with functional text that can be read by assistive technology.

The easiest method to provide this accessible alternative is to write HTML code which includes the <noscript> tag.  Other options include ensuring that dynamic content and refreshes can be made or are accessible.

Applets, Objects, Plug-ins

When a web page requires that an applet, plug-in or other application be present on the client system to interpret page content, the page must provide a link to a plug-in or applet that complies with §1194.21(a) through (l).

Objects and data which require plug-in applications can be presented in HTML code in a nested manner such that, if the user's browser can't display the topmost data type, it will attempt to display equivalent data type in the object specification.  This is more complicated HTML code to create and requires several data types to be resident on the server, but it is a more complete method of inclusion which favors neither advanced nor dated browser technology.


When electronic forms are designed to be completed on-line, the form shall allow people using assistive technology to access the information, field elements, and functionality required for completion and submission of the form, including all directions and cues.

Incomplete.  To be completed soon.

Content tracking

A method shall be provided that permits users to skip repetitive navigation tasks.

There are a number of methods of facilitating navigation for users of assistive technology.  Be consistent in page-to-page design, designers can provide a jump-link to bypass a series of links on a page similar to the "back to top" used in long pages, when using multiple links close together, separate the links so the reader software can parse it correctly.  Links should be referenced with text which make sense if a user if link-jumping.  Also, consider adding a site map, which is useful to nearly everyone.

Timed Response

When a timed response is required, the user shall be alerted and given sufficient time to indicate more time is required.

Incomplete.  To be completed soon.
Table 2-1 (taken from the U.S. Architectural and Transportation Barriers Compliance Board Recommendations)

The sites listed below are online tools which can help assess a site's accessibility.

This document was assembled to assist NASA and other Federal webmasters in the goal of making all Government websites accessible. Additional links and/or source material is invited. Please forward suggestions or corrections to Jayne Dutra, JPL, Co-chair, or Robin Land, LaRC, Co-Chair, NASA Webmasters, or Charles Redmond, NASA HQ Webmaster.

If you have any difficulty viewing this page with adaptive technology, click here to let us know.

Charles Redmond
NASA Headquarters
NASA Headquarters building picture Curator
Charles Redmond
This document last updated January 22, 2001.