mdanalysis

A Python toolkit for examining molecular-dynamics simulations, which are computer-generated movies of atoms moving over time.

In plain words
What is it for?
Use it to calculate RMSD and RMSF, align structures, study contacts and hydrogen bonds, inspect dihedral angles and secondary structure, analyze principal motions, and estimate diffusion or density.
Why use it?
It turns simulation trajectories into measurements that show whether a protein is stable, how flexible it is, and how a drug interacts with it.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/kdevos12/alkyl/mdanalysis
Any agent
npx skills add Kdevos12/ALKYL --skill mdanalysis
Clone the repo
git clone --depth 1 https://github.com/Kdevos12/ALKYL

Made for: Claude Code, Codex.

Per session 49 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,026 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00049 $0.01026
Opus 5 $0.00024 $0.00513
Sonnet 5 $0.00010 $0.00205
Haiku 4.5 $0.00005 $0.00103

Measured 2d ago against content hash f6097ecf620d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mdanalysis 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 2d 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/mdanalysis/SKILL.md · 102 lines

How it starts

The opening of the file, as written. The whole thing — 102 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MDAnalysis — MD Trajectory Analysis

MDAnalysis 2.10.0 (2025). Core pattern: Universe (topology + trajectory) → AtomGroup (selection) → AnalysisBase.run().results.

When to Use This Skill

  • Loading GROMACS, AMBER, NAMD, CHARMM, LAMMPS trajectories
  • RMSD and RMSF calculations (protein stability, flexibility)
  • Structural alignment across trajectory frames
  • Hydrogen bond detection and lifetime analysis
  • Protein-ligand contacts and binding site analysis
  • Dihedral angles (Ramachandran plots, chi angles)
  • Secondary structure (DSSP) assignment
  • PCA of conformational dynamics
  • Radial distribution functions (RDF), density maps
  • Mean square displacement (MSD), diffusion coefficients

Quick Start

import MDAnalysis as mda
from MDAnalysis.analysis import rms, align

# Load topology + trajectory
u = mda.Universe('protein.prmtop', 'traj.dcd')
print(u)                   # <Universe with 45000 atoms>
print(len(u.trajectory))   # number of frames

# Select atoms
protein = u.select_atoms('protein')
ca      = u.select_atoms('protein and name CA')
ligand  = u.select_atoms('resname LIG')

# Iterate trajectory
for ts in u.trajectory:
    print(ts.frame, ts.time, ca.positions.mean(axis=0))

Router — What to Read

Task Reference
Universe, topology formats, selections, trajectory I/O, writing references/universe-selections.md
RMSD, RMSF, alignment, radius of gyration references/rmsd-rmsf-alignment.md
Hydrogen bonds, native contacts, binding residues references/contacts-hbonds.md
Dihedrals, DSSP, PCA, RDF, density, MSD references/structure-dynamics.md
Protein-ligand interaction analysis workflow references/protein-ligand.md

Key Modules

Module Import Role
rms from MDAnalysis.analysis import rms RMSD, RMSF
align from MDAnalysis.analysis import align Structural alignment
contacts from MDAnalysis.analysis import contacts Native contacts
hydrogenbonds from MDAnalysis.analysis.hydrogenbonds.hbond_analysis import HydrogenBondAnalysis H-bonds
dihedrals from MDAnalysis.analysis.dihedrals import Ramachandran, Janin Dihedral angles
dssp from MDAnalysis.analysis.dssp import DSSP Secondary structure
pca from MDAnalysis.analysis.pca import PCA Conformational PCA
rdf from MDAnalysis.analysis.rdf import InterRDF Radial distribution
density from MDAnalysis.analysis.density import DensityAnalysis Density maps
msd from MDAnalysis.analysis.msd import EinsteinMSD Diffusion
distances from MDAnalysis.analysis.distances import dist, between Distances

Read the full file on GitHub · 102 lines

Files

What ships with it

5 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. 2d ago First seen · 102 lines · 49 tokens per session scan A f6097ecf620d

Subscribe to this mod's changes

mdanalysis is a skill published in the GitHub repository Kdevos12/ALKYL (6 stars, last pushed 5mo ago), licensed MIT. It adds 49 tokens to every session and 1,026 once invoked, about $0.0002 per session on Opus 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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