retrosynthesis-planning

retrosynthesis-planning is a skill for Claude Code, Codex from PharMolix/OpenBioMed. It costs 48 tokens per session (1,638 once invoked), scanned A, original, MIT.

A chemistry planning workflow that works backward from a target molecule to find possible starting materials and synthesis steps, with a human chemist able to review the route.

In plain words
What is it for?
Use it to plan synthetic routes for complex molecules, test each proposed reaction in the forward direction, and verify terminal starting materials against chemical suppliers or local databases.
Why use it?
It helps avoid routes based on impossible reactions or materials that cannot be obtained. It also checks whether proposed building blocks are available to buy.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to plan synthetic routes for complex molecules, test each proposed reaction in the forward direction, and verify terminal starting materials against chemical suppliers or local databases.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/pharmolix/openbiomed/retrosynthesis-planning
About the project

OpenBioMed is an agent platform and toolkit collection for biomedical research and drug discovery, covering areas such as molecular design, protein analysis, and single-cell data analysis. It is intended for researchers and provides the biomedical skills listed in the catalogue as workflows for Claude Code.

PharMolix/OpenBioMed · 1,106 stars · on GitHub

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 PharMolix/OpenBioMed --skill retrosynthesis-planning
Clone the repo
git clone --depth 1 https://github.com/PharMolix/OpenBioMed

Made for: Claude Code, Codex.

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 retrosynthesis-planning

README.md
[![agentmods](https://agentmods.dev/badge/skills/pharmolix/openbiomed/retrosynthesis-planning/github.svg)](https://agentmods.dev/skills/pharmolix/openbiomed/retrosynthesis-planning)
Your own site
<a href="https://agentmods.dev/skills/pharmolix/openbiomed/retrosynthesis-planning"><img src="https://agentmods.dev/badge/skills/pharmolix/openbiomed/retrosynthesis-planning/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 retrosynthesis-planning

Your own site · 80×15
<a href="https://agentmods.dev/skills/pharmolix/openbiomed/retrosynthesis-planning"><img src="https://agentmods.dev/badge/skills/pharmolix/openbiomed/retrosynthesis-planning.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 48 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,638 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. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 $0.00048 $0.01638
Opus 5 $0.00024 $0.00819
Sonnet 5 $0.00010 $0.00328
Haiku 4.5 $0.00005 $0.00164

Measured 11d ago against content hash 8c4dddf8b779, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

retrosynthesis-planning 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 11d ago.

The scan reads SKILL.md. This mod also ships 4 executable files (scripts/analyze_molecule.py, scripts/render_tree.py, scripts/retro_engine.py, …), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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/retrosynthesis-planning/SKILL.md · 54 lines

How it starts

The opening of the file, as written. The whole thing — 54 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Retrosynthetic Planning Expert

You are an expert computational chemist and synthetic planner. Your primary role is to assist in the retrosynthetic analysis of complex target molecules, working either autonomously or in an "expert-in-the-loop" setting with the user.

Core Objectives

  1. Algorithmic Disconnection (AiZynthFinder / ML Integration): Prioritize querying external chemical reasoning engines or locally deployed open source agents (e.g., AiZynthFinder) for single-step retro-disconnections to obtain high-confidence, literature-backed templates. Ensure hybrid reasoning (LLM + ML backend).
  2. Forward Reaction Validation (Anti-Hallucination): For every proposed retrosynthetic disconnection, rigorously evaluate the forward reaction. Check if it genuinely produces the target molecule with high yield, without impossible chemo- or regio-selectivity clashes.
  3. Starting Material Availability (API Verification): Actively query chemical vendor APIs (eMolecule, MolPort, or local compound databases) to verify if terminal nodes are directly purchasable. Terminate search branches when a valid commercial building block is found.
  4. *State Management & Tree Search Strategies (MCTS / A)**: Maintain an AND/OR structural tree via scripts/route_state_manager.py. Molecule nodes (OR layers) demand at least one valid reaction, while Reaction nodes (AND layers) demand all fragment children are solvable/purchasable. Rely on its automatic backpropagation (solved status pushing to root) to track ultimate pipeline success over deep sequences.
  5. RDKit Rule Scripting via Code Gen: Write and execute RDKit Python scripts on-the-fly to validate expert heuristics (e.g., ring strain, protecting group orthogonality, steric hindrance calculations) and strictly normalize any LLM-generated SMILES to canonical RDKit SMILES.

Workflow: Two Distinct Modes

At the very beginning of the session, you MUST explicitly ask the user whether they want to use Mode A or Mode B, rather than deciding based on how the session was started. Wait for the user's response before proceeding.

Read the full file on GitHub · 54 lines

Files

What ships with it

8 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. 11d ago First seen · 54 lines · 48 tokens per session scan A 8c4dddf8b779

Subscribe to this mod's changes

retrosynthesis-planning is a skill published in the GitHub repository PharMolix/OpenBioMed (1,106 stars, last pushed 1mo ago), licensed MIT. It adds 48 tokens to every session and 1,638 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 2026-08-30.

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