rdkit

rdkit is a skill for Claude Code from Kdevos12/ALKYL. It costs 58 tokens per session (1,151 once invoked), scanned A, original, MIT.

A guide to RDKit, a Python library for reading, changing, searching, measuring, and visualizing chemical molecules.

In plain words
What is it for?
It is for working with molecule files and SMILES, calculating properties, filtering drug-like compounds, comparing fingerprints, generating 3D shapes, searching substructures, handling reactions, and drawing molecules.
Why use it?
It provides ready-made approaches for common cheminformatics tasks instead of requiring you to implement molecular representations and analyses yourself.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the alkyl plugin — 27 skills shipped together

Good fit It is for working with molecule files and SMILES, calculating properties, filtering drug-like compounds, comparing fingerprints, generating 3D shapes, searching substructures, handling reactions, and drawing molecules.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/kdevos12/alkyl/rdkit
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add Kdevos12/ALKYL --skill rdkit
Clone the repo
git clone --depth 1 https://github.com/Kdevos12/ALKYL

Made for: Claude Code.

Or install alkyl, the plugin that ships this one along with the rest of its 27 skills.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for rdkit

README.md
[![agentmods](https://agentmods.dev/badge/skills/kdevos12/alkyl/rdkit/github.svg)](https://agentmods.dev/skills/kdevos12/alkyl/rdkit)
Your own site
<a href="https://agentmods.dev/skills/kdevos12/alkyl/rdkit"><img src="https://agentmods.dev/badge/skills/kdevos12/alkyl/rdkit/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for rdkit

Your own site · 80×15
<a href="https://agentmods.dev/skills/kdevos12/alkyl/rdkit"><img src="https://agentmods.dev/badge/skills/kdevos12/alkyl/rdkit.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 58 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,151 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00058 $0.01151
Opus 5.5 $0.00023 $0.00460
Sonnet 5.5 $0.00012 $0.00230
Haiku 4.5 $0.00006 $0.00115

Measured 1mo ago against content hash 3c1e9e5c3069, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

rdkit scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/rdkit/SKILL.md · 97 lines

How it starts

The opening of the file, as written. The whole thing — 97 lines — stays where its author put it; the contents beside it link to each section on GitHub.

RDKit

The primary Python library for cheminformatics. Molecular manipulation, descriptors, fingerprints, 3D generation, reactions, and more.

When to Use This Skill

  • Reading/writing molecules from SMILES, SDF, MOL, PDB files
  • Calculating molecular properties and drug-likeness filters (Ro5, QED)
  • Computing and comparing molecular fingerprints (Morgan/ECFP, MACCS, RDKit FP)
  • Generating 3D conformers (ETKDG, MMFF, UFF)
  • Substructure searching and SMARTS queries
  • Maximum Common Substructure (MCS) analysis
  • Chemical reactions via SMARTS or RXN files
  • Molecular fragmentation (BRICS, RECAP, Murcko scaffolds)
  • Stereochemistry assignment and analysis
  • Tautomer enumeration and molecule standardization
  • Molecular visualization (2D SVG/PNG, similarity maps)

Quick Start

from rdkit import Chem
from rdkit.Chem import AllChem, Descriptors, Draw, rdMolDescriptors

# Load molecule
mol = Chem.MolFromSmiles('CC(=O)Oc1ccccc1C(=O)O')  # aspirin

# Basic properties
print(Descriptors.MolWt(mol))        # 180.16
print(Descriptors.MolLogP(mol))      # 1.31
print(rdMolDescriptors.CalcNumHBD(mol))  # 1
print(rdMolDescriptors.CalcNumHBA(mol))  # 4
print(rdMolDescriptors.CalcTPSA(mol))    # 63.6

# Morgan fingerprint (ECFP4-like)
fpgen = AllChem.GetMorganGenerator(radius=2)
fp = fpgen.GetFingerprint(mol)

# 2D image
img = Draw.MolToImage(mol, size=(300, 200))

Router — What to Read

Task Reference
SMILES, SDF, MOL, PDB, SMARTS I/O, serialization references/io-molecules.md
Descriptors, Lipinski Ro5, QED, ADME, drug filters references/properties-descriptors.md
Morgan, MACCS, RDKit FP, atom pair, similarity, diversity references/fingerprints-similarity.md
3D conformers (ETKDG), MMFF/UFF optimization, 3D descriptors references/3d-conformers.md
Reactions (SMARTS), BRICS, RECAP, Murcko, tautomers, standardization references/transformations.md
Substructure search (SMARTS), MCS, rings, stereochemistry, pharmacophores references/analysis-search.md
Visualization: SVG/PNG, highlighting, similarity maps, grids references/visualization.md

Read the full file on GitHub · 97 lines

Files

What ships with it

7 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago First seen · 97 lines · 58 tokens per session scan A 3c1e9e5c3069

Subscribe to this mod's changes

rdkit is a skill published in the GitHub repository Kdevos12/ALKYL (7 stars, last pushed 7mo ago), licensed MIT. It adds 58 tokens to every session and 1,151 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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