Conda package specification

Package metadata

The info/ directory contains all metadata about a package. Files in this location are not installed under the install prefix. Although you are free to add any file to this directory, conda only inspects the content of the files discussed below.


  • files

    • a list of all the files in the package (not included in info/)

  • index.json

    • metadata about the package including platform, version, dependencies, and build info

  "arch": "x86_64",
  "build": "py37hfa4b5c9_1",
  "build_number": 1,
  "depends": [
    "depend > 1.1.1"
  "license": "BSD 3-Clause",
  "name": "fun-packge",
  "platform": "linux",
  "subdir": "linux-64",
  "timestamp": 1535416612069,
  "version": "0.0.0"
  • paths.json

    • a list of files in the package, along with their associated SHA-256, size in bytes, and the type of path (eg. hardlink vs. softlink)

  "paths": [
      "_path": "lib/python3.7/site-packages/fun-packge/",
      "path_type": "hardlink",
      "sha256": "76f3b6e34feeb651aff33ca59e0279c4eadce5a50c6ad93b961c846f7ba717e9",
      "size_in_bytes": 2067
      "_path": "lib/python3.7/site-packages/fun-packge/",
      "path_type": "hardlink",
      "sha256": "348e3602616c1fe4c84502b1d8cf97c740d886002c78edab176759610d287f06",
      "size_in_bytes": 87519


This file contains basic information about the package, such as name, version, build string, and dependencies. The content of this file is stored in repodata.json, which is the repository index file, hence the name index.json. The JSON object is a dictionary containing the keys shown below. The filename of the conda package is composed of the first 3 values, as in: <name>-<version>-<build>.tar.bz2.






The lowercase name of the package. May contain the "-" character.



The package version. May not contain "-". Conda acknowledges PEP 440.



The build string. May not contain "-". Differentiates builds of packages with otherwise identical names and versions, such as:

  • A build with other dependencies, such as Python 3.4 instead of Python 2.7.

  • A bug fix in the build process.

  • Some different optional dependencies, such as MKL versus ATLAS linkage. Nothing in conda actually inspects the build string. Strings such as np18py34_1 are designed only for human readability and conda never parses them.



A non-negative integer representing the build number of the package.

Unlike the build string, the build_number is inspected by conda. Conda uses it to sort packages that have otherwise identical names and versions to determine the latest one. This is important because new builds that contain bug fixes for the way a package is built may be added to a repository.


list of strings

A list of dependency specifications, where each element is a string, as outlined in Package match specifications.



Optional. The architecture the package is built for.

EXAMPLE: x86_64

Conda currently does not use this key.



Optional. The OS that the package is built for.


Conda currently does not use this key. Packages for a specific architecture and platform are usually distinguished by the repository subdirectory that contains them---see Repository structure and index.


Lists all files that are part of the package itself, 1 per line. All of these files need to get linked into the environment. Any files in the package that are not listed in this file are not linked when the package is installed. The directory delimiter for the files in info/files should always be "/", even on Windows. This matches the directory delimiter used in the tarball.


Optional file. Lists all files that contain a hard-coded build prefix or placeholder prefix, which needs to be replaced by the install prefix at installation time.


Due to the way the binary replacement works, the placeholder prefix must be longer than the install prefix.

Each line of this file should be either a path, in which case it is considered a text file with the default placeholder /opt/anaconda1anaconda2anaconda3, or a space-separated list of placeholder, mode, and path, where:

  • Placeholder is the build or placeholder prefix.

  • Mode is either text or binary.

  • Path is the relative path of the file to be updated.

EXAMPLE: On Windows:

"C:\Users\username\anaconda\envs\_build" text "Scripts/script2.bat"
"C:/Users/username/anaconda/envs/_build" binary "Scripts/binary"

EXAMPLE: On macOS or Linux:

/Users/username/anaconda/envs/_build binary bin/binary
/Users/username/anaconda/envs/_build text share/text


The directory delimiter for the relative path must always be "/", even on Windows. The placeholder may contain either "\" or "/" on Windows, but the replacement prefix will match the delimiter used in the placeholder. The default placeholder /opt/anaconda1anaconda2anaconda3 is an exception, being replaced with the install prefix using the native path delimiter. On Windows, the placeholder and path always appear in quotes to support paths with spaces.


Optional file. The software license for the package.


Optional file. Contains the entries in the about section of the meta.yaml file. The following keys are added to info/about.json if present in the build recipe:

  • home

  • dev_url

  • doc_url

  • license_url

  • license

  • summary

  • description

  • license_family


A directory containing the full contents of the build recipe.


The fully rendered build recipe. See conda render.

This directory is present only when the the include_recipe flag is True in the build section.

Repository structure and index

A conda repository - or channel - is a directory tree, usually served over HTTPS, which has platform subdirectories, each of which contain conda packages and a repository index. The index file repodata.json lists all conda packages in the platform subdirectory. Use conda index to create such an index from the conda packages within a directory. It is simple mapping of the full conda package filename to the dictionary object in info/index.json described in link scripts.

In the following example, a repository provides the conda package misc-1.0-np17py27_0.tar.bz2 on 64-bit Linux and 32-bit Windows:

<some path>/linux-64/repodata.json


Both conda packages have identical filenames and are distinguished only by the repository subdirectory that contains them.

Package match specifications

This match specification is not the same as the syntax used at the command line with conda install, such as conda install python=3.9. Internally, conda translates the command line syntax to the spec defined in this section.

EXAMPLE: python=3.9 is translated to python 3.9*.

Package dependencies are specified using a match specification. A match specification is a space-separated string of 1, 2, or 3 parts:

  • The first part is always the exact name of the package.

  • The second part refers to the version and may contain special characters:

    • | means OR.

      EXAMPLE: 1.0|1.2 matches version 1.0 or 1.2

    • * matches 0 or more characters in the version string. In terms of regular expressions, it is the same as r.*````.

      EXAMPLE: 1.0|1.4* matches 1.0, 1.4 and 1.4.1b2, but not 1.2.

    • <, >, <=, >=, == and != are relational operators on versions, which are compared using PEP-440. For example, <=1.0 matches 0.9, 0.9.1, and 1.0, but not 1.0.1. == and != are exact equality.

      Pre-release versioning is also supported such that >1.0b4 will match 1.0b5 and 1.0rc1 but not 1.0b4 or 1.0a5.

      EXAMPLE: <=1.0 matches 0.9, 0.9.1, and 1.0, but not 1.0.1.

    • , means AND.

      EXAMPLE: >=2,<3 matches all packages in the 2 series. 2.0, 2.1 and 2.9 all match, but 3.0 and 1.0 do not.

    • , has higher precedence than |, so >=1,<2|>3 means greater than or equal to 1 AND less than 2 or greater than 3, which matches 1, 1.3 and 3.0, but not 2.2.

    Conda parses the version by splitting it into parts separated by |. If the part begins with <, >, =, or !, it is parsed as a relational operator. Otherwise, it is parsed as a version, possibly containing the "*" operator.

  • The third part is always the exact build string. When there are 3 parts, the second part must be the exact version.

Remember that the version specification cannot contain spaces, as spaces are used to delimit the package, version, and build string in the whole match specification. python >= 2.7 is an invalid match specification. Furthermore, python>=2.7 is matched as any version of a package named python>=2.7.

When using the command line, put double quotes around any package version specification that contains the space character or any of the following characters: <, >, *, or |.


conda install numpy=1.11
conda install numpy==1.11
conda install "numpy>1.11"
conda install "numpy=1.11.1|1.11.3"
conda install "numpy>=1.8,<2"


The OR constraint "numpy=1.11.1|1.11.3" matches with 1.11.1 or 1.11.3.

The AND constraint "numpy>=1.8,<2" matches with 1.8 and 1.9 but not 2.0.

The fuzzy constraint numpy=1.11 matches 1.11, 1.11.0, 1.11.1, 1.11.2, 1.11.18, and so on.

The exact constraint numpy==1.11 matches 1.11, 1.11.0,, and so on.

The build string constraint "numpy=1.11.2=*nomkl*" matches the NumPy 1.11.2 packages without MKL but not the normal MKL NumPy 1.11.2 packages.

The build string constraint "numpy=1.11.1|1.11.3=py36_0" matches NumPy 1.11.1 or 1.11.3 built for Python 3.6 but not any versions of NumPy built for Python 3.5 or Python 2.7.

The following are all valid match specifications for numpy-1.8.1-py27_0:

  • numpy

  • numpy 1.8*

  • numpy 1.8.1

  • numpy >=1.8

  • numpy ==1.8.1

  • numpy 1.8|1.8*

  • numpy >=1.8,<2

  • numpy >=1.8,<2|1.9

  • numpy 1.8.1 py27_0

  • numpy=1.8.1=py27_0

Version ordering

The class VersionOrder(object) implements an order relation between version strings.

Version strings can contain the usual alphanumeric characters (A-Za-z0-9), separated into components by dots and underscores. Empty segments (i.e. two consecutive dots, a leading/trailing underscore) are not permitted. An optional epoch number - an integer followed by ! - can precede the actual version string (this is useful to indicate a change in the versioning scheme itself). Version comparison is case-insensitive.

Supported version strings

Conda supports six types of version strings:

  • Release versions contain only integers, e.g. 1.0, 2.3.5.

  • Pre-release versions use additional letters such as a or rc, for example 1.0a1, 1.2.beta3, 2.3.5rc3.

  • Development versions are indicated by the string dev, for example 1.0dev42, 2.3.5.dev12.

  • Post-release versions are indicated by the string post, for example 1.0post1, 2.3.5.post2.

  • Tagged versions have a suffix that specifies a particular property of interest, e.g. 1.1.parallel. Tags can be added to any of the preceding 4 types. As far as sorting is concerned, tags are treated like strings in pre-release versions.

  • An optional local version string separated by + can be appended to the main (upstream) version string. It is only considered in comparisons when the main versions are equal, but otherwise handled in exactly the same manner.

Predictable version ordering

To obtain a predictable version ordering, it is crucial to keep the version number scheme of a given package consistent over time. Conda considers prerelease versions as less than release versions.

  • Version strings should always have the same number of components (except for an optional tag suffix or local version string).

  • Letters/Strings indicating non-release versions should always occur at the same position.

Before comparison, version strings are parsed as follows:

  • They are first split into epoch, version number, and local version number at ! and + respectively. If there is no !, the epoch is set to 0. If there is no +, the local version is empty.

  • The version part is then split into components at . and _.

  • Each component is split again into runs of numerals and non-numerals

  • Subcomponents containing only numerals are converted to integers.

  • Strings are converted to lowercase, with special treatment for dev and post.

  • When a component starts with a letter, the fillvalue 0 is inserted to keep numbers and strings in phase, resulting in 1.1.a1' == 1.1.0a1'.

  • The same is repeated for the local version part.


1.2g.beta15.rc  =>  [[0], [1], [2, 'g'], [0, 'beta', 15], [0, 'rc']]

1!2.15.1_ALPHA  =>  [[1], [2], [15], [1, '_alpha']]

The resulting lists are compared lexicographically, where the following rules are applied to each pair of corresponding subcomponents:

  • Integers are compared numerically.

  • Strings are compared lexicographically, case-insensitive.

  • Strings are smaller than integers, except

    • dev versions are smaller than all corresponding versions of other types.

    • post versions are greater than all corresponding versions of other types.

  • If a subcomponent has no correspondent, the missing correspondent is treated as integer 0 to ensure '1.1' == 1.1.0'.

The resulting order is:

< 0.4.0
< 0.4.1.rc
== 0.4.1.RC   # case-insensitive comparison
< 0.4.1
< 0.5a1
< 0.5b3
< 0.5C1      # case-insensitive comparison
< 0.5
< 0.9.6
< 0.960923
< 1.0
< 1.1dev1    # special case ``dev``
< 1.1a1
< 1.1.0dev1  # special case ``dev``
== 1.1.dev1   # 0 is inserted before string
< 1.1.a1
< 1.1.0rc1
< 1.1.0
== 1.1
< 1.1.0post1 # special case ``post``
== 1.1.post1  # 0 is inserted before string
< 1.1post1   # special case ``post``
< 1996.07.12
< 1!0.4.1    # epoch increased
< 1!
< 2!0.4.1    # epoch increased again

Some packages (most notably OpenSSL) have incompatible version conventions. In particular, OpenSSL interprets letters as version counters rather than pre-release identifiers. For OpenSSL, the relation 1.0.1 < 1.0.1a   =>   True   # for OpenSSL holds, whereas conda packages use the opposite ordering. You can work around this problem by appending a dash to plain version numbers:

1.0.1a  =>  1.0.1post.a      # ensure correct ordering for OpenSSL