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Downloadable reference cards

Three printable reference cards: the full ASCII table, HTTP status codes, and Unix permission digits. The numbers come from the same source as the tables below, and the PDFs are laid out at build time, so the two can never drift apart.

ASCII and code-point reference card

All 128 ASCII code points with decimal, hex, category and UTF-8 width

Download PDF 3 pages · v1.0

The first thing to check when text looks wrong is the code point, not the character. This card lists every one of the 128 ASCII code points with its decimal value, hex value, control abbreviation or glyph, category, and UTF-8 width, so a mismatch can be traced to a number instead of a guess.

When you need it

A control character is hiding in a string and nothing prints it
You need the hex form for a packet dump, a diff, or a regex
A character works in one encoding and breaks in another

Dec	Hex	Char or name	Category	UTF-8 bytes
0	0x00	NUL	Control	1
1	0x01	SOH	Control	1
2	0x02	STX	Control	1
3	0x03	ETX	Control	1
4	0x04	EOT	Control	1
5	0x05	ENQ	Control	1
6	0x06	ACK	Control	1
7	0x07	BEL	Control	1
8	0x08	BS	Control	1
9	0x09	TAB	Control	1
10	0x0A	LF	Control	1
11	0x0B	VT	Control	1
12	0x0C	FF	Control	1
13	0x0D	CR	Control	1
14	0x0E	SO	Control	1
15	0x0F	SI	Control	1
16	0x10	DLE	Control	1
17	0x11	DC1	Control	1
18	0x12	DC2	Control	1
19	0x13	DC3	Control	1
20	0x14	DC4	Control	1
21	0x15	NAK	Control	1
22	0x16	SYN	Control	1
23	0x17	ETB	Control	1
24	0x18	CAN	Control	1
25	0x19	EM	Control	1
26	0x1A	SUB	Control	1
27	0x1B	ESC	Control	1
28	0x1C	FS	Control	1
29	0x1D	GS	Control	1
30	0x1E	RS	Control	1
31	0x1F	US	Control	1
32	0x20	(space)	Whitespace	1
33	0x21	!	Punctuation	1
34	0x22	"	Punctuation	1
35	0x23	#	Punctuation	1
36	0x24	$	Punctuation	1
37	0x25	%	Punctuation	1
38	0x26	&	Punctuation	1
39	0x27	'	Punctuation	1
40	0x28	(	Punctuation	1
41	0x29	)	Punctuation	1
42	0x2A	*	Punctuation	1
43	0x2B	+	Punctuation	1
44	0x2C	,	Punctuation	1
45	0x2D	-	Punctuation	1
46	0x2E	.	Punctuation	1
47	0x2F	/	Punctuation	1
48	0x30	0	Digit	1
49	0x31	1	Digit	1
50	0x32	2	Digit	1
51	0x33	3	Digit	1
52	0x34	4	Digit	1
53	0x35	5	Digit	1
54	0x36	6	Digit	1
55	0x37	7	Digit	1
56	0x38	8	Digit	1
57	0x39	9	Digit	1
58	0x3A	:	Punctuation	1
59	0x3B	;	Punctuation	1
60	0x3C	<	Punctuation	1
61	0x3D	=	Punctuation	1
62	0x3E	>	Punctuation	1
63	0x3F	?	Punctuation	1
64	0x40	@	Punctuation	1
65	0x41	A	Uppercase	1
66	0x42	B	Uppercase	1
67	0x43	C	Uppercase	1
68	0x44	D	Uppercase	1
69	0x45	E	Uppercase	1
70	0x46	F	Uppercase	1
71	0x47	G	Uppercase	1
72	0x48	H	Uppercase	1
73	0x49	I	Uppercase	1
74	0x4A	J	Uppercase	1
75	0x4B	K	Uppercase	1
76	0x4C	L	Uppercase	1
77	0x4D	M	Uppercase	1
78	0x4E	N	Uppercase	1
79	0x4F	O	Uppercase	1
80	0x50	P	Uppercase	1
81	0x51	Q	Uppercase	1
82	0x52	R	Uppercase	1
83	0x53	S	Uppercase	1
84	0x54	T	Uppercase	1
85	0x55	U	Uppercase	1
86	0x56	V	Uppercase	1
87	0x57	W	Uppercase	1
88	0x58	X	Uppercase	1
89	0x59	Y	Uppercase	1
90	0x5A	Z	Uppercase	1
91	0x5B	[	Punctuation	1
92	0x5C	\	Punctuation	1
93	0x5D	]	Punctuation	1
94	0x5E	^	Punctuation	1
95	0x5F	_	Punctuation	1
96	0x60	`	Punctuation	1
97	0x61	a	Lowercase	1
98	0x62	b	Lowercase	1
99	0x63	c	Lowercase	1
100	0x64	d	Lowercase	1
101	0x65	e	Lowercase	1
102	0x66	f	Lowercase	1
103	0x67	g	Lowercase	1
104	0x68	h	Lowercase	1
105	0x69	i	Lowercase	1
106	0x6A	j	Lowercase	1
107	0x6B	k	Lowercase	1
108	0x6C	l	Lowercase	1
109	0x6D	m	Lowercase	1
110	0x6E	n	Lowercase	1
111	0x6F	o	Lowercase	1
112	0x70	p	Lowercase	1
113	0x71	q	Lowercase	1
114	0x72	r	Lowercase	1
115	0x73	s	Lowercase	1
116	0x74	t	Lowercase	1
117	0x75	u	Lowercase	1
118	0x76	v	Lowercase	1
119	0x77	w	Lowercase	1
120	0x78	x	Lowercase	1
121	0x79	y	Lowercase	1
122	0x7A	z	Lowercase	1
123	0x7B	{	Punctuation	1
124	0x7C	\|	Punctuation	1
125	0x7D	}	Punctuation	1
126	0x7E	~	Punctuation	1
127	0x7F	DEL	Control	1

U+0000 to U+007F encode as one UTF-8 byte; every code point above that needs two or more.
U+007F is DEL, a control character, not a printable glyph.
LF (10) and CR (13) are the only line endings this table needs to disambiguate: CRLF is both bytes in that order.

HTTP status code reference card

Every registered status code from RFC 9110 and its extensions, grouped by class

Download PDF 2 pages · v1.0

A status code is not a label for how the request felt, it is a machine-readable statement about what happened. This card lists the registered codes with the reason phrase and the one detail that changes the fix — which codes must not carry a body, which ones are cacheable, and which ones ask the client to retry differently.

When you need it

Choosing between 401, 403 and 404 for an authorization failure
Debugging a proxy or CDN that rewrites the status
Answering "is this cacheable" without re-reading the RFC

Code	Reason phrase	What it commits you to
100	Continue	Headers received; the client may send the body
101	Switching Protocols	WebSocket upgrades happen here
102	Processing	WebDAV; accepted, still working
103	Early Hints	Preload hints before the final response
200	OK	Meaning varies by method: GET returns a body, POST a result
201	Created	Should carry Location for the new resource
202	Accepted	Accepted, not finished; poll somewhere
203	Non-Authoritative Information	Body altered by a proxy
204	No Content	No body allowed; metadata headers still legal
205	Reset Content	Client should reset the form view
206	Partial Content	Pairs with Content-Range; the basis of resuming
207	Multi-Status	WebDAV; XML multi-status body
208	Already Reported	WebDAV; avoids re-enumeration
226	IM Used	Delta encoding applied
300	Multiple Choices	Client picks a representation
301	Moved Permanently	Cacheable; the method may be rewritten to GET
302	Found	Temporary; historical clients rewrite the method
303	See Other	Explicitly switch to GET for the result
304	Not Modified	Must carry validators and no body
305	Use Proxy	Deprecated
307	Temporary Redirect	Method and body preserved
308	Permanent Redirect	Permanent 307; cacheable
400	Bad Request	Syntax or parameters invalid
401	Unauthorized	Missing credentials; send WWW-Authenticate
402	Payment Required	Reserved, never enabled
403	Forbidden	Identity known, permission missing; retrying will not help
404	Not Found	Also used to conceal whether a resource exists
405	Method Not Allowed	Must carry Allow
406	Not Acceptable	Accept negotiation failed
407	Proxy Authentication Required	Proxy-level authentication
408	Request Timeout	Server gave up waiting for the request
409	Conflict	State conflict, typically concurrent writes
410	Gone	Was here, deliberately gone; safe to purge from an index
411	Length Required	Content-Length is required
412	Precondition Failed	An If-Match style precondition failed
413	Content Too Large	Body exceeds the server limit
414	URI Too Long	Target URI too long
415	Unsupported Media Type	Content-Type not supported
416	Range Not Satisfiable	Should carry Content-Range: bytes */length
417	Expectation Failed	Expect header cannot be met
418	I'm a teapot	An April 1st joke that RFC 9110 still reserves
421	Misdirected Request	Connection reused for a host it does not serve
422	Unprocessable Content	Syntax fine, semantics rejected
423	Locked	WebDAV resource locked
424	Failed Dependency	WebDAV; a prior action failed
425	Too Early	Anti-replay; early data refused
426	Upgrade Required	Protocol upgrade demanded
428	Precondition Required	Conditional request required to avoid lost updates
429	Too Many Requests	Should carry Retry-After
431	Request Header Fields Too Large	Header block exceeds the limit
451	Unavailable For Legal Reasons	Unavailable for legal reasons
500	Internal Server Error	Unexpected failure; do not leak internals
501	Not Implemented	Method not recognised
502	Bad Gateway	Upstream returned an invalid response
503	Service Unavailable	Overload or maintenance; send Retry-After
504	Gateway Timeout	Upstream timed out
505	HTTP Version Not Supported	Protocol version unsupported
506	Variant Also Negotiates	Content negotiation misconfigured
507	Insufficient Storage	WebDAV; out of space
508	Loop Detected	WebDAV; loop detected
510	Not Extended	An extension is required
511	Network Authentication Required	Captive portal, typically public Wi-Fi

204 and 304 must not carry a body; a 304 must also repeat the validator headers it compares against.
301 and 308 are permanent and cacheable; 302 and 307 are temporary, and only 307 guarantees the method and body survive.
5xx means the server failed, not the request; 4xx means the request is the problem, except 408 and 429 which are about timing.

Unix permission reference card

Octal digits, rwx triplets, special bits and the modes you actually type

Download PDF 1 pages · v1.0

Permissions are three independent digits, and almost every incident comes from reading them as one word. This card gives what each octal digit prints and grants, what the special bits do, and the modes that show up in real deployments — including why a directory needs the execute bit to be entered even when it is readable.

When you need it

Deciding between 644 and 755 for a deployed file
A script fails with permission denied while ls shows r--
Writing an archive extractor that must restore modes

Digit	Prints as	Grants
0	---	No permission at all
1	--x	Execute only; traverse an exact known path
2	-w-	Write only; truncate and append work, reading does not
3	-wx	Drop-box: create and remove by name, no enumeration
4	r--	Read only; scripts will not run, directories can be listed
5	r-x	The usual directory mode
6	rw-	The usual data-file mode
7	rwx	Full control; the executable-file mode

A mode is three of these digits: 644 is rw- r-- r-- and 755 is rwx r-x r-x.
Special bits sit in front: 4000 setuid, 2000 setgid, 1000 sticky — a 1777 directory lets anyone create files but only owners delete them.
umask subtracts at creation time: with umask 022 a request for 777 lands as 755, and a request for 666 lands as 644.

Reviewed 2026-10-22 PDFs are generated at build time with English labels (embedded Helvetica, Latin characters only)