RDKit Cheminformatics Toolkit

Overview

RDKit is a comprehensive cheminformatics library providing Python APIs for molecular analysis and manipulation. This skill provides guidance for reading/writing molecular structures, calculating descriptors, fingerprinting, substructure searching, chemical reactions, 2D/3D coordinate generation, and molecular visualization. Use this skill for drug discovery, computational chemistry, and cheminformatics research tasks.

Current baseline (checked 2026-06-07): RDKit 2026.03.3 is the latest GitHub/PyPI release (rdkit 2026.3.3 on PyPI). Official installation docs continue to recommend conda-forge for most users, while cross-platform PyPI wheels are published under the rdkit package name. rdkit-pypi is the old PyPI package name and should only appear when maintaining legacy environments.

Installation and Setup

Use uv when installing into an existing Python environment:

bash

uv pip install rdkit

For reproducible chemistry environments, especially when mixing compiled scientific packages, conda-forge remains the upstream recommendation:

bash

conda create -c conda-forge -n my-rdkit-env rdkit
conda activate my-rdkit-env

Avoid installing both conda rdkit and PyPI rdkit/rdkit-pypi into the same environment unless you are deliberately debugging packaging behavior. Mixed installs can make it unclear which binary extension is being imported.

Core Capabilities

Twelve capability areas, each with worked code, are documented in references/core_capabilities.md:

#	Area	Covers
1	Molecular I/O and creation	SMILES, MOL files and blocks, InChI, SDF and SMILES suppliers, multithreaded reading, writers
2	Sanitization and validation	disabling automatic sanitization, manual and partial sanitization, detecting problems first
3	Analysis and properties	atom and bond iteration, ring information and SSSR, chirality and stereochemistry, fragments
4	Descriptors	MW, LogP, TPSA, H-bond donors/acceptors, rotatable bonds, aromatic rings, bulk calculation, drug-likeness
5	Fingerprints and similarity	topological, Morgan/ECFP via `rdFingerprintGenerator`, MACCS, atom pair, torsion, Avalon; Tanimoto and other metrics; Butina clustering
6	Substructure searching	SMARTS queries, match retrieval, and a library of common patterns
7	Chemical reactions	reaction SMARTS, applying reactions, reaction fingerprints
8	2D and 3D coordinates	depiction, template alignment, ETKDG embedding, force-field optimization, RMSD, constrained embedding
9	Visualization	single and grid images, substructure highlighting, custom drawer options, Jupyter integration, fingerprint bit environments
10	Molecular modification	explicit hydrogens, Kekulization, aromaticity, substructure replacement, charge neutralization
11	Hashes and standardization	Murcko scaffold and canonical hashes, regioisomer hashes, randomized SMILES for augmentation
12	Pharmacophore and 3D features	feature factories and feature extraction

Worked workflows and the performance, thread-safety, and version-sensitivity notes are in references/workflows_and_best_practices.md.

Prefer portable exchange formats (SMILES, SDF) for shared data; for local caches RDKit's binary molecule representation avoids generic pickle.

Common Pitfalls

Forgetting to check for None: Always validate molecules after parsing
Sanitization failures: Use DetectChemistryProblems() to debug
Missing hydrogens: Use AddHs() when calculating properties that depend on hydrogen
2D vs 3D: Generate appropriate coordinates before visualization or 3D analysis
SMARTS matching rules: Remember that unspecified properties match anything
Thread safety with MolSuppliers: Don't share supplier objects across threads

Resources

references/

This skill includes detailed API reference documentation:

api_reference.md - Comprehensive listing of RDKit modules, functions, and classes organized by functionality
descriptors_reference.md - Complete list of available molecular descriptors with descriptions
smarts_patterns.md - Common SMARTS patterns for functional groups and structural features

Load these references when needing specific API details, parameter information, or pattern examples.

Only the files listed in references/ and scripts/ are bundled local resources. Names such as rdkit, datamol, scipy, and sklearn refer to installable Python packages, not local files in this skill.

scripts/

Example scripts for common RDKit workflows:

molecular_properties.py - Calculate comprehensive molecular properties and descriptors
similarity_search.py - Perform fingerprint-based similarity screening
substructure_filter.py - Filter molecules by substructure patterns

These scripts can be executed directly or used as templates for custom workflows.