---
title: AiZynthFinder quickstart
description: Five steps from a target SMILES to scored retrosynthesis routes — pick stocks and a policy, submit, then read score, steps and the purchasability flag.
tags:
  - aizynthfinder
  - quickstart
---

You want to plan a synthetic route for a target molecule: paste a single target SMILES, choose your stock sources and template policy, and submit — five steps from a sanitized SMILES to downloadable, scored routes that tell you whether the target is synthetically accessible from commercial starting materials.

## About AiZynthFinder

AiZynthFinder is developed by the **AstraZeneca Molecular AI team** and is one of the leading open-source retrosynthesis planning tools. Version 4.0, published in the *Journal of Cheminformatics* in May 2024, introduced filter policies and bonds-to-freeze constraints for more controlled route generation.

In published benchmarks, AiZynthFinder achieves an **80–86% success rate** for finding routes where all starting materials are commercially available.

## Prerequisites

- AiZynthFinder enabled in your workspace.
- A single target SMILES; ensure it is sanitized, neutralized, and free of disconnected salt fragments.
- At least one stock source selected (public or in-house) — routes are only marked purchasable when every starting material exists in a selected stock.

## Steps

1. Open the AiZynthFinder tool and start a new job.
2. Enter the target SMILES directly, or use **From Previous Job** to pull a compound from a [REINVENT](/docs/reinvent), [GenMol](/docs/genmol), or database-search result.
3. Choose your stocks (for example `zinc`) and expansion policy (`uspto_50k` is a good default), and leave search breadth and depth at their defaults to start.
4. Submit and monitor the job log; transient failures retry automatically. A typical search runs 5–30 minutes depending on molecule complexity.
5. Download routes (JSON/CSV) and review the score, step count, and purchasability flag for each.

## Reading the first result

- **Score (0.0–1.0)**: higher is a more likely route; treat `> 0.8` as high-confidence.
- **Purchasable**: filter for `is_purchasable: true` routes first — those need no custom intermediate synthesis.
- **Length**: fewer steps is generally preferable for the same score.

The result also renders as an interactive retrosynthetic tree on the canvas, with green nodes for in-stock building blocks, yellow for orderable, and red for materials needing custom synthesis. See [outputs & interpretation](/docs/aizynthfinder/outputs) for the full field reference.

## Quick checks

- Confirm the job metadata lists the expected stock set and policy.
- Ensure at least one route is marked purchasable; if none are, revisit your stock choices before concluding the target is inaccessible.
- Save the job URL alongside project notes for reproducibility.

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