I've received a lot of interesting comments and questions from Sudoku fans over the last few years and this page
is where I try to answer them. I'm also directing Str8ts feedback here. Please feel free to drop me a note on the side of the page. Or you can email me directly at andrew@str8ts.com.
Post a Comment or Question here...
Tuesday 21-Oct-2025
... by: Rick, Hong Kong
Hi just want to know how to import/create the custom shape in "Killer Jigsaw Solver". I can create the cages, but cannot the shape. I notice there's custom one to create or import, but failed.
So how should I create it?
Andrew Stuart writes:
Click on the blue button Step 2. I have to separate the two parts of the creation process. Send me a link with the puzzle afterwards, interested to see one I didn't make. Use "Email this board"
Monday 20-Oct-2025
... by: bill, United States
WHY DO I GET THE RESPONSE "reset_yes_no: no row called RUR1"
Andrew Stuart writes:
I split off Unique Rectangles type 1 and put it earlier in the list, must be a month ago. Sounds like you don’t have the latest page. Talking about /Sudoku.htm? Does it say version 2.43.2? Can you press [CRTL]+[F5] to refresh
Send me the puzzle you are working on in case its something else. Use "Email/Export"
Thursday 16-Oct-2025
... by: Rafael, Spain
Hello,
I've been enjoying your solver and your many lessons on the techniques.
I took up sudoku a few months ago and I sit comfortably at the diabolical level now, doing the level 4 sudoku of the day whenever I can.
However, I've noticed that I could not solve some of the last few daily puzzles, and when I gave up and used the "solve path" option, I saw that it required X-Cycles with ALS, listed as diabolical. Is that considered diabolical considering ALS are listed as an Extreme level technique? In my view, combining any AIC (including X-Cycles) with other techniques such as ALS or UR increases the difficulty by a lot.
It's just a silly question, but I hope you can share your insight.
Rafael
Andrew Stuart writes:
Very glad you have been enjoying the puzzle and find the site useful I think you are right. ALS/UR and other exotic links are a bit too much for diabolical grade. I’ll keep grouped-cells inside as they are relatively easy to understand. I’m still tweaking the heuristics for the Daily puzzles so I can do something to flag those puzzles away.
Wednesday 8-Oct-2025
... by: Davin, -
Reply to TenPeter, You don't have to always use rows to cover the S cell candidates. We may use 1 row and 1 column, or 2 columns. In this case the 8s can be covered by 2 columns so it is a valid exocet even with the 8.
Tuesday 7-Oct-2025
... by: FHessel, Universe
Hi Andrew, I'm using this solver (https://www.sudokuwiki.org/KillerJigsaw.aspx) for a long time, not to "cheat", but as an easy means for clearing candidates. Therefore I'm using only the first two steps of the solver: * Check for solved squares * Show Possibles Now there are two concerns:
Number 1: Apparently something has changed recently. We had a conversation about this topic years ago, and for a long time you could do the step "Show Possibles" without being forced by the solver to resolve any single-candidate-square into a solved square. This is convenient with difficult/extreme puzzles, because you could solve a square and apply all implications of this step without considering the whole board over and over again (which you would have to do, when the solver sets some solved squares simultaneously and you lose track). Nowadays the solver enforces every single-candidate-square to be resolved to a solved square before proceeding with the next step.
Number 2: This is a real bug. When the solver does the step "Show Possibles" with the result "No" (having found no candidate to clear), it proceeds with the next strategy steps even when you have changed some squares in the meantime (regardless whether the change was clearing a candidate or solving a square). In other words: after the result "No" the solver won't be reset to start by any change you make on the board.
best regards FHessel
Andrew Stuart writes:
Great to hear from you again. I’ve just noticed a dumb bug on the killer/killer jigsaw solver. The auto clear was broken as I was not checking if a field existed. So I’ve fixed that.
Can I check if you are aware that you can enter a single candidate in a cell by prefixing it with a zero? That will stop it evaluating it as a solved cell
When the solver does the step "Show Possibles" with the result "No"... This is by design to reduce the number of clicks. Killer is already very click “take-step” intensive as you have to chip away at the puzzle for a long time. I’m sure it has been this way from the very start
However there could be some more steps I can think about. Tell me you are using it with Auto clear off and the zero trick and let me know if that is not quite addressing the problem
Monday 6-Oct-2025
... by: Eves, United States
Hi Andrew Been visiting your site for quite some time now. I just realized that it would be cool to have a 6x6 Mini Sudoku Solver and additional puzzles added to your site. With Mini Sudoku becoming popular thanks to LinkedIn games, I would love to see support for Mini Sudoku.
Andrew Stuart writes:
I think I could manage that :) Will add to the job queue
Sunday 5-Oct-2025
... by: Bellmac, Bellingham, WA USA
Solved the #6487 Level 3 puzzle for October 5. The new scoring system gives this a Tough Grade of 6.0 (old score 132, Tough). I am at a bit of loss how this puzzle gets a score this high, under either system. No tough strategies are needed. 23 steps are required: 15 naked singles, 4 hidden singles, 2 naked pairs, and 2 naked triples. So, this is a pretty simple puzzle that ought to be no higher than Moderate, based on my experience.
Also, I do not really understand the new numeric difficulty scale. From the discussion, it appears that total range goes to 9+ for Sudoku, which is open-ended. Most scales have a defined fixed length (e.g. 1 to 10 or 1 to 100). And I am not sure why there is a decimal point, which tends to create an impression of precision, which may not be warranted. I think it would be better to eliminate the decimal and go to a 1 to 100 scale.
Andrew Stuart writes:
Good feedback, thanks for writing in. I’ve delayed writing until now as the new rating system wasn’t good enough on the first pass and I’d updated it on the 6th. I agree this puzzle is a moderate (solver now says so) and but I’d uploaded new stock for that week. The old score is not wholly static either as over time adding new strategies and moving the order changes things a bit.
What’s it been like after the 6th? I’m hoping it is more aligned now.
Regards your points about the scale I think until we know for sure how to rate unsolvables, ie be able to solve logically all puzzles, we don’t know what the end of the scale looks like. It is possible to generate a very high score in puzzles right on the edge where many hard patterns are required to chip away at the candidates. I wanted to stretch the scale to put more mileage between publishable puzzles and the crazy extremes. But going into five figures gives the illusion of precision as you say. So I’m using a log function to bring it all back down to a 1 to 10+ but an integer is a bit too granular in my opinion.
Tuesday 30-Sep-2025
... by: TenPeter, USA
Continuing the discussion with Ayumu below. A Junior Exocet pattern requires no more than 2 cover houses for a candidate Base Pair digit. The subject Exocet has the digit 8 on three different rows (F,G&J) in the cover lines thus it requires 3 cover houses to cover the digit 8. This can be seen in the screen capture that you provided. This implies that this is not a valid Exocet pattern. If your were to eliminate the digit 8 from the Base Pair, then the remaining three digits (2,3,4) would form a valid Exocet.
Monday 29-Sep-2025
... by: Bellmac, Bellingham, WA USA
Solved Level 3 puzzle for today (#6481, September 29, 2025). The current scoring system release gives this a Tough Grade of 122. This seems way too high considering the puzzle solution has 19 Naked Singles, 6 Hidden Singles, and 2 Naked Pairs, none of which are Tough Strategies or above.
However, I noticed that your new beta version 4.7 scoring system gives this a Moderate score, which seems much more appropriate. So, looks like you are making good progress on revising the scoring system.
Andrew Stuart writes:
I am hoping people will notice and let me know if it is working. Will take some time to appraise the difference and I think we need a decent sample. I tested the two daily puzzles you wrote to me a few weeks ago. They seem to adjust their grade in the right direction.
From 1st of October I am replacing the daily puzzle stock. For the rest of the year I am picking puzzles which happen to have the same grade in both systems. This should remove puzzles that might have been problematic but also be a good transition. I’ll continue to post both scores for easy comparison. Will write up a page about it today to explain it.
Tuesday 21-Oct-2025
... by: Rick, Hong Kong
So how should I create it?
Monday 20-Oct-2025
... by: bill, United States
Send me the puzzle you are working on in case its something else. Use "Email/Export"
Thursday 16-Oct-2025
... by: Rafael, Spain
I've been enjoying your solver and your many lessons on the techniques.
I took up sudoku a few months ago and I sit comfortably at the diabolical level now, doing the level 4 sudoku of the day whenever I can.
However, I've noticed that I could not solve some of the last few daily puzzles, and when I gave up and used the "solve path" option, I saw that it required X-Cycles with ALS, listed as diabolical. Is that considered diabolical considering ALS are listed as an Extreme level technique? In my view, combining any AIC (including X-Cycles) with other techniques such as ALS or UR increases the difficulty by a lot.
It's just a silly question, but I hope you can share your insight.
Rafael
I think you are right. ALS/UR and other exotic links are a bit too much for diabolical grade. I’ll keep grouped-cells inside as they are relatively easy to understand. I’m still tweaking the heuristics for the Daily puzzles so I can do something to flag those puzzles away.
Wednesday 8-Oct-2025
... by: Davin, -
You don't have to always use rows to cover the S cell candidates. We may use 1 row and 1 column, or 2 columns.
In this case the 8s can be covered by 2 columns so it is a valid exocet even with the 8.
Tuesday 7-Oct-2025
... by: FHessel, Universe
I'm using this solver (https://www.sudokuwiki.org/KillerJigsaw.aspx) for a long time, not to "cheat", but as an easy means for clearing candidates.
Therefore I'm using only the first two steps of the solver:
* Check for solved squares
* Show Possibles
Now there are two concerns:
Number 1:
Apparently something has changed recently. We had a conversation about this topic years ago, and for a long time you could do the step "Show Possibles" without being forced by the solver to resolve any single-candidate-square into a solved square.
This is convenient with difficult/extreme puzzles, because you could solve a square and apply all implications of this step without considering the whole board over and over again (which you would have to do, when the solver sets some solved squares simultaneously and you lose track). Nowadays the solver enforces every single-candidate-square to be resolved to a solved square before proceeding with the next step.
Number 2:
This is a real bug. When the solver does the step "Show Possibles" with the result "No" (having found no candidate to clear), it proceeds with the next strategy steps even when you have changed some squares in the meantime (regardless whether the change was clearing a candidate or solving a square). In other words: after the result "No" the solver won't be reset to start by any change you make on the board.
best regards
FHessel
I’ve just noticed a dumb bug on the killer/killer jigsaw solver. The auto clear was broken as I was not checking if a field existed. So I’ve fixed that.
Can I check if you are aware that you can enter a single candidate in a cell by prefixing it with a zero? That will stop it evaluating it as a solved cell
When the solver does the step "Show Possibles" with the result "No"...
This is by design to reduce the number of clicks. Killer is already very click “take-step” intensive as you have to chip away at the puzzle for a long time. I’m sure it has been this way from the very start
However there could be some more steps I can think about. Tell me you are using it with Auto clear off and the zero trick and let me know if that is not quite addressing the problem
Monday 6-Oct-2025
... by: Eves, United States
Been visiting your site for quite some time now. I just realized that it would be cool to have a 6x6 Mini Sudoku Solver and additional puzzles added to your site. With Mini Sudoku becoming popular thanks to LinkedIn games, I would love to see support for Mini Sudoku.
Will add to the job queue
Sunday 5-Oct-2025
... by: Bellmac, Bellingham, WA USA
Also, I do not really understand the new numeric difficulty scale. From the discussion, it appears that total range goes to 9+ for Sudoku, which is open-ended. Most scales have a defined fixed length (e.g. 1 to 10 or 1 to 100). And I am not sure why there is a decimal point, which tends to create an impression of precision, which may not be warranted. I think it would be better to eliminate the decimal and go to a 1 to 100 scale.
What’s it been like after the 6th? I’m hoping it is more aligned now.
Regards your points about the scale I think until we know for sure how to rate unsolvables, ie be able to solve logically all puzzles, we don’t know what the end of the scale looks like. It is possible to generate a very high score in puzzles right on the edge where many hard patterns are required to chip away at the candidates. I wanted to stretch the scale to put more mileage between publishable puzzles and the crazy extremes. But going into five figures gives the illusion of precision as you say. So I’m using a log function to bring it all back down to a 1 to 10+ but an integer is a bit too granular in my opinion.
Tuesday 30-Sep-2025
... by: TenPeter, USA
Monday 29-Sep-2025
... by: Bellmac, Bellingham, WA USA
However, I noticed that your new beta version 4.7 scoring system gives this a Moderate score, which seems much more appropriate. So, looks like you are making good progress on revising the scoring system.
From 1st of October I am replacing the daily puzzle stock. For the rest of the year I am picking puzzles which happen to have the same grade in both systems. This should remove puzzles that might have been problematic but also be a good transition. I’ll continue to post both scores for easy comparison. Will write up a page about it today to explain it.
Sunday 28-Sep-2025
... by: flix, yurp
Load Sudoku: CLICK TO LOADwhen trying to grade this one, your program exits with D5 cell empty.
has one solution.
think its a bug.
best regards