Is a Caesar cipher secure?

No. With only 25 useful shifts anyone can try them all in seconds, which is what the brute-force table does. The page carries a warning that this is a puzzle cipher and not encryption.

Which characters are shifted?

Only the ASCII letters A to Z and a to z. Digits, punctuation, spaces and accented letters are unchanged, or dropped if you turn off preserving non-letters.

How does the brute-force table pick the likely answer?

It compares each candidate's letter frequencies with typical English using a chi-squared score and flags the lowest. It works best on longer English text, so trust your eyes on short or non-English messages.

Why does running ROT13 twice give back the original?

Thirteen is half of 26, so a second shift of 13 returns every letter to where it began. Encoding and decoding with ROT13 are therefore the same operation.

Text toolsInstantPrivateNo account

Caesar Cipher

The Caesar cipher tool shifts each letter of your text forward or back by a number of places, from 0 to 25, with a one-click ROT13 button.

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About Caesar cipher

The Caesar cipher tool shifts each letter of your text forward or back by a number of places, from 0 to 25, with a one-click ROT13 button. It also has a brute-force table that shows all 25 possible decodings of a message and highlights the most English-looking one. It is intended for puzzles, classes and geocaching, not for protecting secrets.

How to use it

Type or paste your text into the input box.
Choose Encode (shift forward) or Decode (shift back) under Direction.
Move the Shift slider or type a number, or press ROT13 to set it to 13.
Copy or download the output. Scroll to the Brute force table when you do not know the key.

Shift of three, then cracked

Input

Meet at the bridge at 9!  (shift 3)

Output

Phhw dw wkh eulgjh dw 9!

When to use it

Solving a Caesar-style puzzle in a geocache, escape room or classroom exercise.
Hiding a spoiler in a forum post using ROT13 so readers must choose to decode it.
Demonstrating in a lesson why a small key space makes a cipher weak.
Recovering the shift used on an old message by scanning the brute-force list.

Good to know. Turning off Preserve letter case makes the output uppercase. The brute-force table decodes only the first 2,000 characters. Everything runs in your browser.

Questions about Caesar cipher

Is a Caesar cipher secure?: No. With only 25 useful shifts anyone can try them all in seconds, which is what the brute-force table does. The page carries a warning that this is a puzzle cipher and not encryption.
Which characters are shifted?: Only the ASCII letters A to Z and a to z. Digits, punctuation, spaces and accented letters are unchanged, or dropped if you turn off preserving non-letters.
How does the brute-force table pick the likely answer?: It compares each candidate's letter frequencies with typical English using a chi-squared score and flags the lowest. It works best on longer English text, so trust your eyes on short or non-English messages.
Why does running ROT13 twice give back the original?: Thirteen is half of 26, so a second shift of 13 returns every letter to where it began. Encoding and decoding with ROT13 are therefore the same operation.

Related tools

Text toolsInstantPrivateNo account

Caesar Cipher

The Caesar cipher tool shifts each letter of your text forward or back by a number of places, from 0 to 25, with a one-click ROT13 button.

Back to category

WorkbenchClient-side · Private

About Caesar cipher

How to use it

Type or paste your text into the input box.
Choose Encode (shift forward) or Decode (shift back) under Direction.
Move the Shift slider or type a number, or press ROT13 to set it to 13.
Copy or download the output. Scroll to the Brute force table when you do not know the key.

Shift of three, then cracked

Input

Meet at the bridge at 9!  (shift 3)

Output

Phhw dw wkh eulgjh dw 9!

When to use it

Solving a Caesar-style puzzle in a geocache, escape room or classroom exercise.
Hiding a spoiler in a forum post using ROT13 so readers must choose to decode it.
Demonstrating in a lesson why a small key space makes a cipher weak.
Recovering the shift used on an old message by scanning the brute-force list.

Good to know. Turning off Preserve letter case makes the output uppercase. The brute-force table decodes only the first 2,000 characters. Everything runs in your browser.

Questions about Caesar cipher

Is a Caesar cipher secure?: No. With only 25 useful shifts anyone can try them all in seconds, which is what the brute-force table does. The page carries a warning that this is a puzzle cipher and not encryption.
Which characters are shifted?: Only the ASCII letters A to Z and a to z. Digits, punctuation, spaces and accented letters are unchanged, or dropped if you turn off preserving non-letters.
How does the brute-force table pick the likely answer?: It compares each candidate's letter frequencies with typical English using a chi-squared score and flags the lowest. It works best on longer English text, so trust your eyes on short or non-English messages.
Why does running ROT13 twice give back the original?: Thirteen is half of 26, so a second shift of 13 returns every letter to where it began. Encoding and decoding with ROT13 are therefore the same operation.

Related tools

WorkbenchClient-side · Private

This is a puzzle cipher, not encryption

A Caesar shift has only 25 possible keys, so anyone can break it instantly — the brute-force panel below does exactly that. Never use it to protect anything real. For actual secrecy, use the AES encrypt & decrypt tool.

Text

Cipher settings

Direction

Shift3

Any whole number works — negative and oversized shifts wrap around to 0–25.

Preserve letter case

Preserve digits, punctuation and spaces

Result

Wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj.

Brute force — all 25 shifts

Every possible decoding of the text above. The row we score as the most English-like is flagged, but trust your eyes over the guess.

Shift	Decoded text	Copy
1	Sgd pthbj aqnvm enw itlor nudq sgd kzyx cnf.
2	Rfc osgai zpmul dmv hsknq mtcp rfc jyxw bme.
3	Qeb nrfzh yoltk clu grjmp lsbo qeb ixwv ald.
4	Pda mqeyg xnksj bkt fqilo kran pda hwvu zkc.
5	Ocz lpdxf wmjri ajs ephkn jqzm ocz gvut yjb.
6likely	Nby kocwe vliqh zir dogjm ipyl nby futs xia.
7	Max jnbvd ukhpg yhq cnfil hoxk max etsr whz.
8	Lzw imauc tjgof xgp bmehk gnwj lzw dsrq vgy.
9	Kyv hlztb sifne wfo aldgj fmvi kyv crqp ufx.
10	Jxu gkysa rhemd ven zkcfi eluh jxu bqpo tew.
11	Iwt fjxrz qgdlc udm yjbeh dktg iwt apon sdv.
12	Hvs eiwqy pfckb tcl xiadg cjsf hvs zonm rcu.
13	Gur dhvpx oebja sbk whzcf bire gur ynml qbt.
14	Ftq cguow ndaiz raj vgybe ahqd ftq xmlk pas.
15	Esp bftnv mczhy qzi ufxad zgpc esp wlkj ozr.
16	Dro aesmu lbygx pyh tewzc yfob dro vkji nyq.
17	Cqn zdrlt kaxfw oxg sdvyb xena cqn ujih mxp.
18	Bpm ycqks jzwev nwf rcuxa wdmz bpm tihg lwo.
19	Aol xbpjr iyvdu mve qbtwz vcly aol shgf kvn.
20	Znk waoiq hxuct lud pasvy ubkx znk rgfe jum.
21	Ymj vznhp gwtbs ktc ozrux tajw ymj qfed itl.
22	Xli uymgo fvsar jsb nyqtw sziv xli pedc hsk.
23	Wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj.
24	Vjg swkem dtqyp hqz lworu qxgt vjg ncba fqi.
25	Uif rvjdl cspxo gpy kvnqt pwfs uif mbaz eph.

This is a puzzle cipher, not encryption

Text

Cipher settings

Direction

Shift3

Any whole number works — negative and oversized shifts wrap around to 0–25.

Preserve letter case

Preserve digits, punctuation and spaces

Result

Wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj.

Brute force — all 25 shifts

Every possible decoding of the text above. The row we score as the most English-like is flagged, but trust your eyes over the guess.

Shift	Decoded text	Copy
1	Sgd pthbj aqnvm enw itlor nudq sgd kzyx cnf.
2	Rfc osgai zpmul dmv hsknq mtcp rfc jyxw bme.
3	Qeb nrfzh yoltk clu grjmp lsbo qeb ixwv ald.
4	Pda mqeyg xnksj bkt fqilo kran pda hwvu zkc.
5	Ocz lpdxf wmjri ajs ephkn jqzm ocz gvut yjb.
6likely	Nby kocwe vliqh zir dogjm ipyl nby futs xia.
7	Max jnbvd ukhpg yhq cnfil hoxk max etsr whz.
8	Lzw imauc tjgof xgp bmehk gnwj lzw dsrq vgy.
9	Kyv hlztb sifne wfo aldgj fmvi kyv crqp ufx.
10	Jxu gkysa rhemd ven zkcfi eluh jxu bqpo tew.
11	Iwt fjxrz qgdlc udm yjbeh dktg iwt apon sdv.
12	Hvs eiwqy pfckb tcl xiadg cjsf hvs zonm rcu.
13	Gur dhvpx oebja sbk whzcf bire gur ynml qbt.
14	Ftq cguow ndaiz raj vgybe ahqd ftq xmlk pas.
15	Esp bftnv mczhy qzi ufxad zgpc esp wlkj ozr.
16	Dro aesmu lbygx pyh tewzc yfob dro vkji nyq.
17	Cqn zdrlt kaxfw oxg sdvyb xena cqn ujih mxp.
18	Bpm ycqks jzwev nwf rcuxa wdmz bpm tihg lwo.
19	Aol xbpjr iyvdu mve qbtwz vcly aol shgf kvn.
20	Znk waoiq hxuct lud pasvy ubkx znk rgfe jum.
21	Ymj vznhp gwtbs ktc ozrux tajw ymj qfed itl.
22	Xli uymgo fvsar jsb nyqtw sziv xli pedc hsk.
23	Wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj.
24	Vjg swkem dtqyp hqz lworu qxgt vjg ncba fqi.
25	Uif rvjdl cspxo gpy kvnqt pwfs uif mbaz eph.

Search tools

Caesar Cipher

About Caesar cipher

How to use it

Shift of three, then cracked

When to use it

Questions about Caesar cipher

Is a Caesar cipher secure?

Which characters are shifted?

How does the brute-force table pick the likely answer?

Why does running ROT13 twice give back the original?

Related tools

Caesar Cipher

About Caesar cipher

How to use it

Shift of three, then cracked

When to use it

Questions about Caesar cipher

Is a Caesar cipher secure?

Which characters are shifted?

How does the brute-force table pick the likely answer?

Why does running ROT13 twice give back the original?

Related tools