Fingerprint format (fpt)#

Generate or display molecular fingerprints.

This format constructs and displays fingerprints and (for multiple input objects) the Tanimoto coefficient and whether a superstructure of the first object.

A list of available fingerprint types can be obtained by:

babel -L fingerprints

The current default type FP2 is is of the Daylight type, indexing a molecule based on the occurrence of linear fragment up to 7 atoms in length. To use a fingerprint type other than the default, use the -xf option, for example:

babel -ofpt -xfFP3

For a single molecule the fingerprint is output in hexadecimal form (intended mainly for debugging).

With multiple molecules the hexadecimal form is output only if the -xh option is specified. But in addition the Tanimoto coefficient between the first molecule and each of the subsequent ones is displayed. If the first molecule is a substructure of the target molecule a note saying this is also displayed.

The Tanimoto coefficient is defined as:

Number of bits set in (patternFP & targetFP) / Number of bits in (patternFP | targetFP)

where the boolean operations between the fingerprints are bitwise.

The Tanimoto coefficient has no absolute meaning and depends on the design of the fingerprint.

Use the -xs option to describe the bits that are set in the fingerprint. The output depends on the fingerprint type. For Fingerprint FP4, each bit corresponds to a particular chemical feature, which are specified as SMARTS patterns in SMARTS_InteLigand.txt, and the output is a tab-separated list of the features of a molecule. For instance, a well-known molecule gives:

Primary_carbon: Carboxylic_acid: Carboxylic_ester: Carboxylic_acid_derivative:
Vinylogous_carbonyl_or_carboxyl_derivative: Vinylogous_ester: Aromatic:
Conjugated_double_bond: C_ONS_bond: 1,3-Tautomerizable: Rotatable_bond: CH-acidic:

For the path-based fingerprint FP2, the output from the -xs option is instead a list of the chemical fragments used to set bits, e.g.:

$ obabel -:"CCC(=O)Cl" -ofpt -xs -xf FP2
0 6 1 6 <670>
0 6 1 6 1 6 <260>
0 8 2 6 <623>

where the first digit is 0 for linear fragments but is a bond order for cyclic fragments. The remaining digits indicate the atomic number and bond order alternatively. Note that a bond order of 5 is used for aromatic bonds. For example, bit 623 above is the linear fragment O=C (8 for oxygen, 2 for double bond and 6 for carbon).


This is a write-only format.

Write Options#

-f <id>

fingerprint type

-N <num>

fold to specified number of bits, 32, 64, 128, etc.


hex output when multiple molecules


hex output only


describe each set bit


describe each unset bit