---
pretty_name: "File format magic numbers"
license: other
license_name: source-terms-cited
license_link: https://referencesource.org/file-format-signatures/
language:
- en
tags:
- reference-data
- provenance
- referencesource-org
configs:
- config_name: default
  data_files:
  - split: train
    path: data/records.jsonl
---
# File format magic numbers

**Canonical, always-current version: https://referencesource.org/file-format-signatures/**
Machine-readable: https://referencesource.org/file-format-signatures/data.json — this mirror is a point-in-time copy.

- **Last verified:** 2026-09-22
- **Stale after:** 2027-09-22 (past this date, prefer the canonical copy —
  it re-verifies on a cadence this snapshot does not)
- **Records:** 337

The leading bytes (magic number / file signature) that identify a file format, with its usual extension. Answers 'what actually is this file' when the extension is wrong or missing. Covers what Wikipedia's List of file signatures publishes — a broad cross-section, not every format that exists.

## Provenance — what every record carries

Every record carries `source` (the URL the value was read from) and
`source_quote` (a verbatim quote from that page stating it). A value you
cannot check against its page is indistinguishable from an invented one;
these can all be checked. Each record is also individually addressable on
the canonical site at its `url`.

## Licence position

CC BY-SA 4.0 (source: Wikipedia)

Facts are not copyrightable; what this dataset takes from each source is a
fact plus a short attributed quote linking back to the page that states it.

## Sources

- https://en.wikipedia.org/wiki/List_of_file_signatures

## Fields

See any record in `data/records.jsonl` — field names are self-describing,
and the canonical page for each record renders them with labels:
https://referencesource.org/file-format-signatures/