3char - Same Code, Different Worlds

3char refers to three-character codes widely used in international standards and registries, such as ISO, alpha-3, IATA, ICAO.

These codes are everywhere, from software and databases to international standards. But the same sequence of characters can appear in different systems, sometimes representing the same thing and sometimes something entirely different.

Although they serve different purposes, these codes share a fundamental characteristic: their meaning depends on the system in which they are defined. The same three characters can exist in multiple systems, sometimes referring to the same thing and sometimes to entirely different things.

Inspired by these 3 character conventions, 3char has evolved into a collection of 64 reference systems containing 817,340 records. It now includes identifiers of different lengths, symbols and controlled vocabularies, organized in a common Parquet schema with their original namespaces, provenance and licensing information preserved. A code can therefore be validated, looked up or compared across systems without losing track of who defined it or on what terms it may be reused.

The data

The 64 systems cover ten domains: biology, classification, computing, communication, finance, graph vocabularies, language, lexical resources, transport and place, and writing and time. They are not all the same kind of list, and the kind says what an entry is:

Kind	Systems	What an entry is	Examples
Assigned code	33	A code issued or registered by an authority	ISO 3166-1 country codes, ICD-10-CM, HGNC gene symbols, PDB entry IDs, ISO 10383 market identifiers
Symbol	9	A position in a fixed table defined by a standard	Chemical element symbols, amino acid codes, Morse and ITA2 signals, Unicode emoji sequences
Vocabulary term	19	A name defined by a specification or a reference document	schema.org and SHACL terms, x86 instruction mnemonics, CSS named colors, CLDR month abbreviations
Community convention	2	A code in common use, kept by a project rather than issued by an authority	File extensions, FourCC codec identifiers
Test vector	1	An example input with its expected output, not an assigned code	The reference test cases of the Open Location Code encoder

Every record has a code and a label. Entries also differ in status within a list: the HTTP status code registry is included with its unassigned values expanded to one row each (436 rows, marked unassigned), six sources keep entries they mark as no longer in use (7,357 rows, marked deprecated), and 43 entries of the PDB ID list that have since been withdrawn are marked obsolete. Each system's kind, authority, size, license status and regular expression are in All 64 systems at the end of this card.

Records

Every system has the same Arrow schema, with one row per entry. São Paulo's airport in the IATA list:

{"system_id": "trp/iata", "code": "GRU",
 "label": "São Paulo/Guarulhos–Governor André Franco Montoro International Airport",
 "description": null, "parent_code": null, "status": null, "aliases": [],
 "extra": "{\"country\": \"BR\", \"municipality\": \"São Paulo\", \"scheduled\": \"yes\", \"type\": \"large_airport\"}"}

Column	Type	Content
system_id	string	<domain>/<id>; joins to the systems configuration
code	string	The entry as the source writes it, without case folding
label	string	Name of the entry, from the source or from the label source named in the system's notes
description	string	Longer description, when a source provides one
parent_code	string	The parent the source assigns, in 17 systems; see below
status	string	Status value published by the source, or null
aliases	list	Other strings that refer to the same entry
extra	string	JSON object with the fields particular to the source

parent_code usually points to another entry of the same system: an ICD-10-CM category, an ATC group, a Library of Congress class, a schema.org supertype. In three systems it names a group that has no row of its own: the EC sub-subclass in bio/ec (1.1.1.-), the top-level type in cmp/mim (application) and the ISO 3166-1 alpha-2 country in trp/unl (BR).

status is null in 758,213 rows. Elsewhere it holds the value the source publishes: approved for every HGNC symbol (44,997 rows); deprecated in bio/ec, cmp/mim, fin/mic, lng/b47, lng/i63 and trp/ica2 (7,357 rows); current for the remaining airlines in trp/ica2 (1,069); unassigned in cmp/sts (436); obsolete for withdrawn PDB entries (43); and the Unicode emoji qualification values in wrt/uni: fully-qualified (3,944), minimally-qualified (1,029), unqualified (243) and component (9). Each source has its own vocabulary, so filter on status within a single system.

extra is a JSON string rather than a struct because the sources have little in common beyond the code and the label: the 59 systems that use it have 142 distinct keys between them, and only 27 of those keys occur in more than one system.

Identifying a record

code is unique within 60 of the 64 systems. In the other four, a record is identified by the fields below, as computed by keys.py:

System	Rows	Distinct codes	Key	Remaining duplicates
trp/unl	116,213	26,162	extra.locode (country plus code)	139 locodes occur on more than one row as bilingual variants of the same name, adding 146 rows
lng/b47	9,295	9,037	code and extra.type	None
wrt/tz	777	769	code and extra.kind	None; eight strings, such as CET and EST, are both a zone name and an abbreviation
wrt/abj	84	83	code and label	None; the repeated code, U+05BC, appears once as dagesh and once as mapiq

Across systems, a record is identified by (system_id, code), or by (system_id, extra.locode) in trp/unl. A code without its system does not identify a record.

Loading

from datasets import load_dataset

ds   = load_dataset("brennercruvinel/3char", "all")        # every system in one table, 817,340 rows
iata = load_dataset("brennercruvinel/3char", "trp-iata")   # a single system
meta = load_dataset("brennercruvinel/3char", "systems")    # 64 rows: authority, URL, license, regex, version, retrieval date

There are 66 configurations: all, systems, and one per system, named <domain>-<id>, so the trp-iata configuration holds the rows whose system_id is trp/iata. Each configuration has a single train split; the data is reference material and has not been divided into training and evaluation sets. For reproducible work, pin a revision with load_dataset(..., revision="<commit sha>").

Uses

• Validating and normalizing codes. A system's rows tell whether a string is an entry in the recorded edition of the list; its regular expression tells whether the string has the form the source defines.
• Grounding language models and search. The lists serve as lookup tables or retrieval corpora that map codes to names and back. Retrieval shows how much the way a record is written changes what comes back.
• Studying codes across systems. The same string often occurs in several lists, sometimes for the same entity and sometimes not, and Results measures both. The closed study poc-nsi used seven systems this way to test whether language models confuse such codes.
• Linking tables. Country codes in extra, such as extra.country in the airport and UN/LOCODE systems and extra.iso3 in lng/ioc, connect several systems to ISO 3166-1; Similarity between systems lists every such field.

Two cautions. The data is a snapshot of the editions listed in Construction: for work that depends on the current edition, such as billing with ICD-10-CM, compare version and retrieved_at with the source's latest release. And 3char is not a crosswalk: apart from the links tested in Lists that describe the same entities, it does not state that entries of different systems denote the same thing.

Results

Every figure in this section is computed from the published files. The census, the keys, the equivalences, the similarity measures and the Wikidata comparison come from scripts in 3char-pipeline (census.py, keys.py, equivalences.py, similarity.py, crosscheck_wikidata.py), whose outputs are kept in its deposit/ folder. The retrieval results come from 3char-bench.

Codes shared between systems

Codes are compared after case folding, and a code is shared when the same folded string occurs in two or more systems. Of the 687,733 distinct folded codes in the 64 systems:

Codes	Count
In exactly one system	672,328
In two or more systems	15,405
In three or more systems	10,269
In eleven systems, the maximum	2 (and, car)
In two or more systems, counting the derived pair lng/b47 and lng/i63 once	15,339

Several lists are almost entirely contained in others. Every code in eight systems also occurs in at least one other: bio/aa1, bio/aa3, bio/cdn, lng/i31, lng/i39, lng/i63, lng/mdy and wrt/iau. In trp/iata, lng/ioc, lng/i15, trp/ica2 and fin/i42, more than 98% of codes do. Without case folding there are 697,391 distinct strings, of which 21,771 occur in more than one system. Within trp/unl, 18,748 codes repeat because the key is the country plus the code; these repetitions are not counted as sharing between systems.

A shared string is not a shared meaning. CAR, one of the two codes claimed by eleven systems, is among other things Caribou Municipal Airport in the IATA list, the Galibi Carib language among the language subtags, the constellation Carina, Avis Budget Group among SEC tickers, a top-level domain and the schema.org and vCard term Car. The census counts strings; the next two sections ask when they denote the same thing.

Similarity between systems

similarity.py compares every pair of systems that share at least 10 codes, 196 pairs in all. For each pair it counts the shared codes and how many of them carry the same name in both systems, after removing accents, case and punctuation.

Each cell gives the share of the row system's codes that the column system also has; pairs sharing fewer than 10 codes are left blank. Opened on its own, the SVG shows the counts of each cell on hover.

Each dot is a pair of systems. The horizontal axis counts the codes they share; the vertical axis gives the share of those codes that carry the same name in both.

Leaving out the derived pair lng/b47 and lng/i63, 8 of the 195 pairs give the same name to more than half of their shared codes: schema.org with Activity Streams (31 of 31), vCard (30 of 30), SIOC (10 of 10), FOAF (14 of 15) and SHACL (13 of 14); ISO 3166-1 with the IOC list (116 of 126); and the BCP 47 registry with ISO 639-1 (152 of 183) and ISO 15924 (182 of 224). At the other end, 179 pairs name fewer than 1% of their shared codes the same way. The largest overlaps are coincidences of the three-letter space: the IATA list shares 8,999 codes with UN/LOCODE and 5,795 with the language subtags, and AAA is Anaa Airport in the first, Araçuaí in the second and the Ghotuo language in the third. Name matching undercounts the IATA and UN/LOCODE overlap, where one list names the airport and the other the place; the next section tests that link with its own rule.

Some systems point to others explicitly. 32 fields have at least 90% of their values among the codes of another system, such as extra.iso3 in lng/ioc, which resolves one to one in ISO 3166-1; the aliases of Glottolog languoids, 95.9% of which are three-letter language subtags; and extra.country in the airport and UN/LOCODE systems, which resolves to ISO 3166-1 alpha-2 region subtags. The full list, with coverage and cardinality, is in deposit/similarity.json.

Lists that describe the same entities

The same entity often appears in several lists, sometimes under the same code and sometimes under a different one. equivalences.py tests each such link with a stated rule. Names are compared after removing accents, case and punctuation, so two different spellings of one name do not match.

Solid lines: same code, same entity. Dashed lines: different codes, same entity. Dotted line: same code, entity not checked. Each label gives the entries of the first list that pass the test, out of all its entries.

Same code, same entity. The BCP 47 subtag registry contains most of three other lists: 152 of the 183 ISO 639-1 codes, 182 of the 226 ISO 15924 codes and 233 of the 249 ISO 3166-1 alpha-2 codes are subtags in it with the same name, and all 8,084 entries of lng/i63 are taken from it. The IOC uses the ISO 3166-1 alpha-3 code for 116 of its 226 countries. The largest overlap is between airport codes and UN/LOCODE: 7,106 of the 9,056 IATA codes are also UN/LOCODE codes in the same country, at a location with the airport function. Names cannot confirm this match, because one list names the airport and the other the place.

Different codes, same entity. The one- and three-letter amino acid codes map one to one (20 of 20). Through extra.iso3, 94 IOC codes point to a different ISO 3166-1 code with the same name, as GER does to DEU. In Glottolog, 6,716 glottocodes carry an ISO 639-3 code that is a three-letter subtag with the same name. Of the IATA airports, 7,725 match exactly one ICAO airport with the same name, municipality and country. And 25 characters have both an ITA2 combination and a Morse signal.

The 244 ISO 3166-1 alpha-2 codes that are also top-level domains are drawn but not counted as the same entity, because the TLD list names the registry that manages each domain, not the country. Across the whole collection, counting the derived pair once, 501 of the 15,339 shared codes carry the same name in two systems. Name matching misses equivalences whose names differ, the IATA and UN/LOCODE overlap among them, so this count is a lower bound on shared meaning, not an estimate of it.

Shared strings by code length

For codes made only of ASCII letters, the table compares the share of claimed strings that more than one system claims with the share expected if each system drew its codes uniformly at random from the 26^L strings of its length.

Length	Possible strings	Claimed	In two or more systems	Observed share	Uniform null	Ratio
1	26	26	25	0.962	0.999	0.96
2	676	521	394	0.756	0.751	1.01
3	17,576	17,151	12,703	0.741	0.919	0.81
4	456,976	19,560	853	0.044	0.015	2.9
5	11,881,376	4,476	65	0.015	0.0001	121

The three-letter space is nearly full: 97.6% of all possible strings are claimed by at least one system, and the observed share of sharing is below the uniform null. From four letters on, the observed share is 2.9 and 121 times the null. The null ignores letter frequencies and word-likeness, and no null matched to those properties has been computed, so the ratios measure departure from a uniform draw and nothing more.

Agreement with Wikidata format constraints

Thirteen systems correspond to a Wikidata external-identifier property with a format constraint (P1793). Every code in these systems was tested for a full match against the property's regular expression, as retrieved on 2026-10-13, in the form the property expects: ICD-10-CM codes with the dot (the CDC file omits it), complete UN/LOCODEs, and, for BCP 47, language subtags only, because P305 describes complete tags.

System	Property	Tested	Rejected	Cause, verified in the source file
lng/i39, lng/i63, lng/ioc, bio/pdb, fin/i42, lng/i15, wrt/tz, cls/loc	P218, P220, P984, P638, P498, P506, P6687, P1149	All	0	None
trp/unl	P1937	116,213	0	None for the complete locode; the three-character code alone cannot match the pattern
cls/icd	P4229	98,403	628	600 FY2027 codes have a letter in the third position (C4A, D3A, M1A) and 28 belong to the new QA0 category; the expression requires digits in the second and third positions
lng/glt	P1394	27,177	3	b10b1234, 3adt1234 and ww2p1234 have a digit in the first block; the expression requires four letters
bio/gen	P353	44,997	14	Approved symbols containing _ (C4A_2) or readthrough segments longer than seven characters (HSPB2-C11orf52)
lng/b47	P305	8,275	1	The private-use range qaa..qtz, a range entry rather than a subtag

In each divergence, the rejected codes are in the authority's current file and the Wikidata constraint does not admit them. This compares two snapshots; it is not an assessment of Wikidata's accuracy in general.

Retrieval

3char-bench asks how a code list should be written into a dense-retrieval index for the right row to come back. It uses ten systems (2,123 records, seed 20260623) and 51 questions in Portuguese, each with one answer record.

• One record per chunk. Written as a sentence, records reach 92.2% recall@1 with multilingual-e5-small, at 22.6 tokens per answer. The same fields as key=value pairs reach 60.8%, and blocks of 20 records 47.1%. With all-MiniLM-L6-v2, an English model, the best record-level result is 52.9%.
• One system per chunk. The right list ranks first for 82.4% to 90.2% of questions, but a reader must still find the row among 6,000 to 7,500 tokens.
• Bare shared codes. A code shared by several sampled systems retrieves a record of the intended system in 33.0% of 182 cases, the rate of a random choice among those systems. With the system name in both the chunk and the query, it does so in all cases.

With 51 questions, one question is worth 1.96 points of recall, and the results describe this sample and these two models only. The ten systems are unchanged in this release, so the results stand.

Construction

The data is produced by 3char-pipeline, which downloads each source, parses it into the common schema and checks the result. Codes, descriptions and aliases are those of each source; no annotation was added, and the curated layer is the systems table.

A source is included when three conditions hold, each recorded in a column or a file of the pipeline:

Condition	Recorded in
The body that maintains the list is identified, and the file comes from that body or from a derivative of it	systems.authority and systems.url
A regular expression written against the actual file matches every published entry	systems.code_pattern, enforced by validate.py; pattern_status is derived for all 64 systems
The SHA-256 of every file read is recorded	CHECKSUMS.tsv

The license and its status are recorded for every system and published with it (see Licensing). For the two community conventions, the maintaining project is the one named in systems.authority.

Labels. When the main source lists bare codes, the label comes from a second official source, named with its URL and retrieval date in the system's notes and checksummed like the main file: wwPDB and RCSB entry titles for bio/pdb, the IANA Root Zone Database for trp/tld, the NAME line of each manual page for cmp/git, the W3C Activity Streams and ActivityPub recommendations for grf/act, OpenID Connect Discovery and the IANA OAuth metadata registry for grf/oid, RFC 6742 and RFC 7208 for nine cmp/dns types, shared-mime-info, GitHub Linguist and mime-db for cmp/ext, and the SEC CIK lookup file for fin/cus. In cmp/reg the label is the LLVM register class of each register, in wrt/tz the name tzdb's theory.html gives each abbreviation or the UTC offset it stands for, and in grf/gql and grf/lpg the grammar rules that use each keyword.

Every build verifies each file against its recorded checksum and tests each entry against its system's regular expression, and either check stops the build on a mismatch. Time zone abbreviations are those the reference compiler zic writes for the default tzdb build.

The main files of 54 systems were retrieved by 2026-06-16, and those of the other ten (bio/aa1, bio/aa3, cls/icd, cmp/ern, cmp/reg, com/bau, com/mor, com/tlg, grf/sio, lng/mdy) on 2026-09-10; the label sources were retrieved on 2026-10-14. Ten systems come from sources that publish a version string, stored in systems.version: ENZYME 28-Jan-2026, ICD-10-CM FY2027, IANA media types 2026-06-05, the ISO 4217 list of 2026-01-01, the IANA Language Subtag Registry of 2026-05-05 (used by both lng/b47 and lng/i63), Open English WordNet 2024, the IANA TLD list 2026060600, tzdb 2026b and Unicode emoji 17.0. For the other 54, retrieved_at is the only date. Updates are made by re-running the pipeline, which detects any change in a source through its checksum.

Limitations

Labels come from each source and are not reconciled across systems. The same airport is São Paulo/Guarulhos–Governor André Franco Montoro International Airport in trp/iata and trp/icao, and Guarulhos Apt / São Paulo, under BRGRU, in trp/unl. Airports have no city-name alias.

Where a label comes from a second source, it is that source's name for the entry, which is not always the name the main source would use: fin/cus carries the name EDGAR currently registers for each CIK, which may differ from the issuer's name when the CUSIP was mapped; trp/tld names the organization that manages each domain; and cmp/ext records in extra.label_source which of its four sources gave each name.

Coverage follows what sources publish. Standards bodies that publish in English and computing registries are well represented; national schemes outside the United States and the UN system are not yet included. The census describes this collection, so adding a system changes it.

Some systems need care when read:

• trp/unl: code is unique only within a country, and the complete locode is in extra.locode. 139 locodes occur on more than one row, as bilingual variants of the same place name.
• lng/b47: the IANA registry lists subtags, not complete language tags. Seven subtag types are distinguished in extra.type, and a code is unique only within its type.
• lng/i63: the three-letter language subtags published by IANA, not ISO 639-3. RFC 5646 omits the three-letter form when a two-letter subtag exists, so eng, deu and por are absent, and the list includes 115 ISO 639-5 collections and 224 deprecated subtags.
• cls/icd: codes are stored without the dot, as in the CDC order file. In the FY2027 edition, 628 codes have a letter in the second or third position. 11,153 codes that use the placeholder X have a parent_code that is not itself a code in the file, such as E0837X.
• trp/iata, trp/icao: derived from the public-domain OurAirports file, not from IATA or ICAO publications. trp/ica2 is named after its OpenFlights source, which lists IATA and ICAO airline codes; it contains 5,840 three-character ICAO designators and one two-character row.
• com/tlg: parsed from the DjVu XML of a scanned 1901 book, with the columns found on each page. The 15,672 code words come from the pages of the code proper; the front matter, the index and the number tables are left out. Code words keep their OCR errors, and 11,856 carry the OCR of their code number in extra.code_number_ocr.
• wrt/tz: 599 zone names and 178 abbreviations. The abbreviations are those of the default build, without the historical zones in backzone.
• cmp/sts: 500 rows for 64 registered status codes, because IANA's unassigned ranges are expanded to one row per code, labelled Unassigned, with the range IANA writes in extra.range when it gives one.
• trp/olc: the test vectors of the reference encoder, not a registry of assigned codes; the label is the coordinate each code encodes.
• lng/ioc: ISO 3166 alpha-3 codes are in extra.iso3 and FIFA codes in extra.fifa; aliases holds only codes that differ from the IOC code.

Licensing

The dataset has no single license. Each row of the systems configuration records license and license_status. The license column takes 28 distinct values: an SPDX identifier where one applies, and otherwise a short tag defined in LICENSES.md. Of the 64 published systems, 56 have the status ok, 2 have the status check and 6 have the status problem.

• Pending clearance (problem). cls/atc, cls/bsc, cls/dew, fin/cus, fin/mic and trp/w3w are published with license_status = problem: their authorities' published terms restrict redistribution, and permission has been requested from each.
• No stated terms (check). fin/cfi and fin/i42 come from SIX Group, which publishes both lists free of charge but states no terms for redistribution. They are included because the codes are plain facts in worldwide use; this is the curator's judgment, not a grant of rights. Anyone who redistributes them commercially should first obtain SIX Group's terms.
• Copyleft and share-alike (seven systems). cmp/frc (GPL-2.0-or-later) and cmp/git (GPL-2.0-only) are lists extracted from GPL source trees; cmp/vim is under the Vim license; grf/sch and grf/sio are under CC-BY-SA-3.0; lng/i31 is under CC-BY-SA-4.0, the license of its mirror; and trp/ica2 is under ODbL-1.0. Their attribution requirements apply to any redistribution, and the share-alike terms also apply to redistributed copies of the tables.
• ISO code lists. lng/i31 and lng/i39 have the status ok on the basis of their mirrors' licenses. ISO asserts copyright over its code lists, and a mirror's license does not change the upstream terms.
• Not included. SIL's ISO 639-3 table is not part of the collection; lng/i63 is a different list, the three-letter subtags of the IANA registry.

Only Parquet files are published. Raw source files are downloaded by the pipeline and are not stored in either repository.

Related resources

Resource	Contents	Relation to 3char
Bioregistry (2,936 prefixes on 2026-10-14)	A registry of identifier systems, mostly biomedical, with prefixes, regular expressions and resolvers	Describes systems without redistributing their contents; 3char distributes the lists, across ten domains
N2T compact identifier prefixes	Resolver prefixes shared with identifiers.org	As for the Bioregistry. Four 3char IDs (elm, icd, mim, pdb) are also N2T prefixes, and two of them denote other systems there: elm is the ELM database and mim is OMIM
Wikidata external-identifier properties (9,846 with a format constraint, 2026-10-13)	One property per system, with a regular expression and identifiers attached to entities	Identifiers are statements about entities rather than the authority's list; the two are compared in Agreement with Wikidata format constraints
pycountry 26.2.16	ISO 3166-1 (249), ISO 3166-2 (5,046), ISO 4217 (178), ISO 639 (7,923) and ISO 15924 (226), as a Python package built from the Debian iso-codes files	Covers five ISO standards; 3char takes ISO 3166-1, 4217, 639-1 and 15924 from other sources and adds 60 other systems
datasets/country-codes, OurAirports, OpenFlights, IANA registries	Source files for single domains	Sources of individual 3char systems, cited in systems.url

All 64 systems

The reference inventory, grouped by domain. Kinds are those described in The data; licenses, versions, retrieval dates, label sources and curator notes are in the systems configuration.

Biology (bio)

ID	System	Kind	Authority	Codes	License status	Pattern
bio/aa1	Amino acid 1-letter codes	Symbol	IUPAC-IUB JCBN	20	ok	^[A-Z]$
bio/aa3	Amino acid 3-letter codes	Symbol	IUPAC-IUB JCBN	20	ok	^[A-Z][a-z]{2}$
bio/cdn	NCBI genetic codes (codons)	Symbol	NCBI	64	ok	^[ACGTU]{3}$
bio/ec	Enzyme commission numbers	Assigned code	IUBMB / ExPASy	8,441	ok	^\d+\.\d+\.\d+\.(n?\d+|-)$
bio/gen	HGNC gene symbols	Assigned code	HUGO Gene Nomenclature Committee	44,997	ok	^[A-Za-z0-9@#\-\._]+$
bio/pdb	PDB entry IDs	Assigned code	wwPDB / RCSB	254,978	ok	^[1-9][A-Z0-9]{3}$

Classification (cls)

ID	System	Kind	Authority	Codes	License status	Pattern
cls/atc	WHO ATC drug classification	Assigned code	WHO Collaborating Centre for Drug Statistics Methodology	6,440	problem	^[A-V](\d{2}([A-Z]([A-Z](\d{2})?)?)?)?$
cls/bsc	BISAC subject headings	Assigned code	Book Industry Study Group	3,887	problem	^[A-Z]{3}\d{6}$
cls/dew	Dewey decimal summaries	Assigned code	OCLC	525	problem	^\d{3}$
cls/elm	Chemical element symbols	Symbol	IUPAC	118	ok	^[A-Z][a-z]{0,2}$
cls/icd	ICD-10-CM	Assigned code	US CDC / NCHS	98,403	ok	^[A-Z][A-Z0-9]{2,6}$
cls/loc	Library of Congress classification outline	Assigned code	Library of Congress	234	ok	^[A-Z]{1,3}$

Computing (cmp)

ID	System	Kind	Authority	Codes	License status	Pattern
cmp/asm	x86 instruction mnemonics	Vocabulary term	Intel / AMD	1,309	ok	^[A-Z][A-Za-z0-9]{1,15}$
cmp/css	CSS functions	Vocabulary term	W3C CSSWG / MDN	105	ok	^[a-zA-Z][a-zA-Z0-9\-]*$
cmp/dns	DNS resource record types	Assigned code	IANA	97	ok	^([A-Z][A-Z0-9\-]*|\*)$
cmp/ern	POSIX errno names	Assigned code	IEEE / The Open Group	77	ok	^E[A-Z0-9]+$
cmp/ext	File extensions	Community convention	Community	286	ok	^[a-z0-9][a-z0-9.+\-]*$
cmp/frc	FourCC codec identifiers	Community convention	Community / VLC	672	ok	^[A-Za-z0-9\-.:_]{2,4}$
cmp/git	Git subcommands	Vocabulary term	Git project	158	ok	^[a-z][a-z0-9\-]{1,17}$
cmp/hex	CSS named colors	Vocabulary term	W3C CSSWG	148	ok	^[a-z]{3,20}$
cmp/htt	HTTP methods	Assigned code	IANA	41	ok	^([A-Z][A-Z\-]*|\*)$
cmp/mim	Media types	Assigned code	IANA	2,300	ok	^[a-z]+/[a-zA-Z0-9!#$&\-\^_\.\+]+$
cmp/reg	x86-64 register names	Vocabulary term	LLVM Project	257	ok	^[a-z][a-z0-9.()]*$
cmp/sts	HTTP status codes	Assigned code	IANA	500	ok	^\d{3}$
cmp/vim	Vim motion commands	Vocabulary term	Vim project	289	ok	^\S{1,40}$

Communication (com)

ID	System	Kind	Authority	Codes	License status	Pattern
com/bau	Baudot / ITA2 teleprinter codes	Symbol	ITU-T	30	ok	^[A-Z0-9\-]+$
com/mor	Morse code	Symbol	ITU-R	48	ok	^([A-Z0-9\u00c9]|[^\w\s]{1,2})$
com/tlg	ABC universal commercial telegraphic code	Symbol	William Clauson-Thue (1901)	15,672	ok	^[A-Za-z]{4,22}$

Finance (fin)

ID	System	Kind	Authority	Codes	License status	Pattern
fin/cfi	ISO 10962 CFI codes	Assigned code	SIX Group / ISO	1,216	check	^[A-Z]{6}$
fin/cus	CIK to CUSIP mapping	Assigned code	CUSIP Global Services / SEC	43,485	problem	^[0-9A-Za-z]{6}$
fin/i42	ISO 4217 currency codes	Assigned code	SIX Group / ISO	178	check	^[A-Z]{3}$
fin/mic	ISO 10383 market identifier codes	Assigned code	ISO 20022 RA / SWIFT	2,853	problem	^[A-Z0-9]{4}$
fin/tck	SEC company tickers	Assigned code	US SEC	10,405	ok	^[A-Z][A-Z\-]{0,6}$

Graph and vocabulary (grf)

ID	System	Kind	Authority	Codes	License status	Pattern
grf/act	ActivityStreams 2.0 terms	Vocabulary term	W3C	141	ok	^[A-Za-z][A-Za-z0-9]*$
grf/foa	FOAF vocabulary terms	Vocabulary term	FOAF project	75	ok	^[A-Za-z][A-Za-z0-9_]*$
grf/gql	openCypher keywords	Vocabulary term	openCypher / Neo4j	61	ok	^[A-Z][A-Z_]*$
grf/lpg	Property graph schema terms	Vocabulary term	arXiv 2211.10962	26	ok	^[A-Z]{2,9}$
grf/oid	OpenID Connect discovery fields	Vocabulary term	OpenID Foundation	17	ok	^[a-z][a-z0-9_]*$
grf/org	W3C Organization ontology terms	Vocabulary term	W3C	45	ok	^[a-zA-Z][A-Za-z0-9]*$
grf/rdf	RDF Schema terms	Vocabulary term	W3C	15	ok	^[a-zA-Z][A-Za-z0-9]*$
grf/sch	schema.org types and properties	Vocabulary term	schema.org / W3C CG	2,987	ok	^[A-Za-z0-9][A-Za-z0-9]*$
grf/shc	SHACL vocabulary terms	Vocabulary term	W3C	221	ok	^[A-Za-z][A-Za-z0-9\-]*$
grf/sio	SIOC vocabulary terms	Vocabulary term	SIOC Project / DERI	99	ok	^[A-Za-z][A-Za-z0-9_]*$
grf/vcd	vCard ontology terms	Vocabulary term	W3C	146	ok	^[a-zA-Z][A-Za-z0-9\-]*$

Language (lng)

ID	System	Kind	Authority	Codes	License status	Pattern
lng/b47	BCP 47 language subtags	Assigned code	IANA	9,295	ok	^[A-Za-z0-9\-]+(\.\.[A-Za-z0-9\-]+)?$
lng/glt	Glottolog languoid codes	Assigned code	MPI-EVA Leipzig	27,177	ok	^[a-z0-9]{4}\d{4}$
lng/i15	ISO 15924 script codes	Assigned code	Unicode Consortium (RA)	226	ok	^[A-Z][a-z]{3}$
lng/i31	ISO 3166-1 country codes	Assigned code	ISO 3166/MA	249	ok	^[A-Z]{2,3}$
lng/i39	ISO 639-1 language codes	Assigned code	ISO 639/RA	183	ok	^[a-z]{2}$
lng/i63	BCP 47 three-letter language subtags	Assigned code	IANA	8,084	ok	^[a-z]{3}$
lng/ioc	Country codes composite	Assigned code	Community / datasets.io	226	ok	^[A-Z]{2,3}$
lng/mdy	Month names	Vocabulary term	Unicode CLDR	12	ok	^[A-Z][a-z]{2}$

Lexical (nte)

ID	System	Kind	Authority	Codes	License status	Pattern
nte/wnt	English WordNet 2024 synset IDs	Assigned code	Global WordNet Association	120,630	ok	^oewn-\d{8}-[nvasr]$

Transport and place (trp)

ID	System	Kind	Authority	Codes	License status	Pattern
trp/iata	IATA airport codes	Assigned code	IATA	9,056	ok	^[A-Z]{3}$
trp/ica2	IATA and ICAO airline codes	Assigned code	IATA / ICAO	5,841	ok	^[A-Z0-9]{2,3}$
trp/icao	ICAO airport codes	Assigned code	ICAO	10,153	ok	^[A-Z]{4}$
trp/olc	Open Location Code (plus codes)	Test vector	Google	292	ok	^[023456789CFGHJMPQRVWX]{4,}\+[23456789CFGHJMPQRVWX]*$
trp/tld	Top level domains	Assigned code	IANA	1,437	ok	^[A-Z0-9\-]+$
trp/unl	UN/LOCODE location codes	Assigned code	UNECE	116,213	ok	^[A-Z0-9]{3}$
trp/w3w	what3words API surface	Vocabulary term	what3words	6	problem	^[a-zA-Z][a-zA-Z0-9_]*$

Writing and time (wrt)

ID	System	Kind	Authority	Codes	License status	Pattern
wrt/abj	Hebrew script characters	Symbol	Unicode / community	84	ok	^\S$
wrt/iau	IAU constellation abbreviations	Assigned code	International Astronomical Union	88	ok	^[A-Z][A-Za-z]{2}$
wrt/tz	tz database zone names and abbreviations	Assigned code	IANA / tzdb	777	ok	^[A-Za-z0-9+\-_/]{1,32}$
wrt/uni	Unicode emoji sequences	Symbol	Unicode Consortium	5,225	ok	^[0-9A-F]{4,6}( [0-9A-F]{4,6})*$

Versions and citation

Releases are numbered MAJOR.MINOR.PATCH: a change to the schema increments the major version, a change to any Parquet file the minor version, and a change limited to the documentation the patch version. This card describes 0.2.0.

@misc{cruvinel_3char_2026,
  title   = {3char: 64 code systems and controlled vocabularies in one schema, with per-system provenance and license status},
  author  = {Cruvinel, Brenner},
  year    = {2026},
  version = {0.2.0},
  url     = {https://huggingface.co/datasets/brennercruvinel/3char}
}