chess games viewer: options help about
The chess games viewer extension saves between sessions the settings listed below.
single large chessboard view
Comment display within the game text: click square B7 (assuming White on bottom) to change whether comments are displayed or not into the move text; when comments are shown, click square C7 (assuming White on bottom) to change how comments are displayed respect to the move text, either inline or on separate lines.
Chessboard move highlight: click square D7 (assuming White on bottom) to toggle the highlighting of the last move's from/to squares.
multiple small chessboards view
Maximum number of shown chessboards: if more games are available than currently shown, the command "m" at the top right of the page allows increasing the number of shown chessboards; if more than one game is currently shown, the "l" command allows reducing the number of shown chessboards; select the number of chessboard that better fits the screen.
reset settings to default values
Click here to reset any stored settings to their default values and to delete any stored data, including analysis engine's data. Reload any open chess games viewer page for the changes to apply.
The chess games viewer extension for Google Chrome is an interactive chessboard showing chess games from links to PGN URLs, from local PGN files and from PGN text, using context menus and page actions.
PGN (Portable Games Notation) files are commonly used by chess websites and by chess software to store and share chess games information. For example, The Week In Chess site is an excellent source of chess news, with games collections and live broadcast of current events.
context menu for links to PGN chess games URLs
A context menu shows chess games from links to PGN chess games URLs.
When hovering on links to PGN chess games URLs, the mouse cursor shows this pointer 
Practice:
right-click this link to a PGN file (notice the mouse cursor pointer when hovening on the link) and select the chess games viewer menu item "view chess games link on a single board".
live refresh mode
The live refresh mode reloads the games periodically until all games are ended, as designed for links to chess games live broadcasts, i.e. links to chess games files periodically updated on their server with new moves from games currently in progress. Many chess tournaments offer such live broadcast links from their websites.
Using the live refresh mode, the chess games viewer assumes the chess games link points to a live broadcast; if the live refresh mode is used instead with a link to a static chess games file, the chess games viewer will likely report that the live broadcast already ended, since the static games file will likely contain no games in progress.
A single large chessboard view is offered as well as a view with multiple small chessboards; click square H5 (assuming White on bottom) to switch between chessboard views. From the multiple small chessboards view, use the commands at the top right of the page to select how many chessboards and which ones are shown; click square A6 (assuming White on bottom) to hide a chessboard.
During a live broadcast, the window title contains a set of three numbers, like "1.2.3 live broadcast" where the first number increases each time a new move is received for the visible games (acting as new move notification), the second is the overall number of live games and the third is the overall number of finished games.
Practice:
right-click this link to a PGN file that simulates a live broadcast and select the chess games viewer menu item "view chess games link on a single board with live refresh" or "view chess games link on multiple boards with live refresh". Click square H5 (assuming White on bottom) to switch between chessboard views.
When using the live refresh mode with this link to a static PGN file, the chess games viewer will not find any game in progress and will report the live broadcast as already ended.
context menu for links to ZIP archives
A context menu for links to ZIP archives offers to inspect each ZIP archive for PGN chess games files. Since ZIP files only occasionally contain chess games in PGN format, those links are not highlighted by the mouse cursor icon; they are also ignored by the page action icon and by the page action popup page (see below).
Loading ZIP archives is a slow process; only the "deflate" and "store" compression methods are supported; encryption is not supported.
Practice:
right-click this link to a ZIP file and select the chess games viewer menu item "inspect ZIP archive link for PGN chess games".
context menu for local PGN and ZIP files
A context menu allows showing chess games from local PGN files and local ZIP archives containing PGN files; the context menu opens the large chessboard view page, click the command 
"files" at the top right of the page to open local files or drag and drop local files on the page.
"files" at the top right of the page to open local files or drag and drop local files on the page.
A browser bookmark can be created for easy access to the chess games viewer page for showing local PGN and ZIP files, simply use the browser command for creating a bookmark from that page.
Practice:
first save as local files this PGN file and this ZIP file, then right-click on the background of this page and select the chess games viewer menu item "open local PGN chess games FILES for viewing on a single board". In the newly opened chessboard page use the command "files" at the top right of the page to open the saved chess games files.
"files" at the top right of the page to open the saved chess games files.
context menu for selected PGN chess games text
A context menu shows chess games from PGN chess games text selected in the web page.
Practice:
select the PGN text below, then right-click and select the chess games viewer menu item "view selected TEXT as PGN chess games on a single board".
[Event "Wch"] [Site "Moscow URS"] [Date "1985.10.15"] [Round "16"] [White "Karpov"] [Black "Kasparov"] [Result "0-1"] [Opening "Sicilian"] [ECO "B44"] 1. e4 c5 2. Nf3 e6 3. d4 cxd4 4. Nxd4 Nc6 5. Nb5 d6 6. c4 Nf6 7. N1c3 a6 8. Na3 d5 9. cxd5 exd5 10. exd5 Nb4 11. Be2 Bc5 12. O-O O-O 13. Bf3 Bf5 14. Bg5 Re8 15. Qd2 b5 16. Rad1 Nd3 17. Nab1 h6 18. Bh4 b4 19. Na4 Bd6 20. Bg3 Rc8 21. b3 g5 22. Bxd6 Qxd6 23. g3 Nd7 24. Bg2 Qf6 25. a3 a5 26. axb4 axb4 27. Qa2 Bg6 28. d6 g4 29. Qd2 Kg7 30. f3 Qxd6 31. fxg4 Qd4+ 32. Kh1 Nf6 33. Rf4 Ne4 34. Qxd3 Nf2+ 35. Rxf2 Bxd3 36. Rfd2 Qe3 37. Rxd3 Rc1 38. Nb2 Qf2 39. Nd2 Rxd1+ 40. Nxd1 Re1+ 0-1
FEN position strings are also a valid text input.
Practice:
select the FEN strings below, then right-click and select the chess games viewer menu item "view selected TEXT as PGN chess games on a single board".
r1bqkb1r/1p3ppp/p1n1pn2/3p4/2P1P3/N1N5/PP3PPP/R1BQKB1R w KQkq - 0 9 8/5pk1/7p/8/1p4P1/1P1R2P1/3N1qBP/3Nr2K w - - 1 41
page action for links to PGN chess games URLs
A page action looks for links to PGN chess games URLs in the current page; if found, a black pawn page action icon 
appears at the right end of the address bar, clicking that icon a popup page allows for opening the links in the chess games viewer.
appears at the right end of the address bar, clicking that icon a popup page allows for opening the links in the chess games viewer.
Practice:
the black pawn icon should have appeared at the right end of the address bar of this page; click that icon to display the popup page and then click the command icons for each link:
for viewing the games on a single board
for viewing the games on a single board with live refresh
for viewing the games on multiple boards with live refresh
for saving the games as a local file
In the popup of this page, "http://stas39.narod.ru/Chess-pgn4web/demoLiveGames.pgn" simulates a live chess broadcast when opened with live refresh; instead, "demoGames.pgn" is a static chess games file with no games in progress and the chess games viewer will report the live broadcast as already ended when opening it with live refresh.
should have appeared at the right end of the address bar of this page; click that icon to display the popup page and then click the command icons for each link:
for viewing the games on a single boardfor viewing the games on a single board with live refreshfor viewing the games on multiple boards with live refreshfor saving the games as a local filechess engine game analysis
The single large chessboard view of the chess games viewer integrates a chess engine for game analysis.
Toggle the chess engine game analysis clicking square H2 of the single large chessboard view. Positive evaluations favor White, while "-1" means Black is approximately a pawn ahead.
When the analysis engine is active, a graph shows the position's evaluation throughout the game. A vertical bar above the horizontal line corresponds to a positive evaluation (White's advantage). The graph uses a logarithmic scale for easier appreciation of small changes for values below 1 pawn unit. The current move is highlighted. Clicking any of the vertical bars moves the chessboard to the corresponding move. Click square G2 for automatic game annotation.
In order to optimize computing resources, the chess games viewer extension allows only one chessboard to be analyzed at any time; when starting analyzing a second chessboard, the analysis of the first chessboard stops. The analysis of each position pauses after 10 minutes. Some analysis engine's data is automatically saved for use in following sessions. The performance the javascript based engine is relatively limited compared to professional engines optimized for each processing environment; use the chess games viewer analysis engine for high-level assessments, for detailed analysis please refer to a chess engine optimized for the chosen computing platform.
endgame tablebase
From the single large chessboard view of the chess games viewer, click square E2 (assuming White on bottom) to probe the online endgame tablebase about the current position. Currently, only positions up to ? men are supported. Please note the endgame tablebase assessment is not integrated with the engine analysis evaluation and graph.
Practice:
probe the online endgame tablebase to discover how many moves White requires to checkmate the Black King starting from the position below.
8/7p/8/8/8/1B6/K6P/2k5 w - - 0 1
user interface help
Interact with the chessboards clicking the squares or using the keyboard; for instance, click square F5 (assuming White on bottom) to display the chess puzzler of the day. Hover the mouse on each square for an help summary. From the single large chessboard view, click square H8 (assuming White on bottom) for detailed help.
Errors alert messages are logged, such as failures to load PGN games, incorrect PGN games or incorrect FEN strings. When an error is encountered, the top left chessboard square will flash to signal the exception. The error alert log can be reviewed clicking the same top left chessboard square.
The chess games viewer extension for Google Chrome is part of the pgn4web project. The pgn4web project's wiki provides more information, including a support page for the chess games viewer extension with answers to frequently asked questions.
credits and license
From the single large chessboard view, click square H8 (assuming White on bottom) for detailed credits and license information for the pgn4web project, released under the terms of the GNU General Public License version 2, and for third party components used by the pgn4web chessboard.
Additional general components of pgn4web applications and used by the chess games viewer extension for Google Chrome: the js-unzip library is licensed by August Lilleaas under the MIT license and the js-inflate library is licensed by August Lilleaas and Masanao Izumo under the MIT license.
Additional components specific to the chess games viewer extension for Google Chrome (see the extension's README.txt file for more details): the GarboChess chess analysis engine is licensed by Gary Linscott under BSD license; the endgame tablebase assessments are from the Lokasoft tablebase webservice; some icons are licensed by Interactivemania under a Creative Commons Attribution-No Derivative Works 3.0 license.
changelog
Major releases of the chess games viewer extension for Google Chrome:
| 2.0.7 | added support for browsing game variations |
| 2.0.4 | added support for Chess Informant symbols |
| 1.9.3 | added detection of web requests for PGN chess games URLs |
| 1.9.2 | added Google Chrome OS file browser integration for PGN and ZIP files |
| 1.8.5 | added support for the online endgame tablebase up to 5 men |
| 1.6.7 | added chess engine for game analysis |
| 1.5.5 | added support for zipped PGN files |
| 1.5.0 | added support for local PGN files, either using the file open dialog box or using drag and drop |
| 1.4.3 | added multiple small chessboards view |
| 1.2.1 | added mouse cursor highlighting for links to PGN chess games URLs |
| 1.1.2 | added page action listing links to PGN chess games URLs |
| 1.0.2 | added live broadcast support added context menus for links to PGN chess games URLs added context menus for selected PGN text initial release of the chess games viewer extension for Google Chrome |
Any release not listed above is a minor release providing small enhancements, general bug fixes, specific support for new releases of the Google Chrome browser or updates of the core pgn4web chessboard.
