---
title: "RENKIN Quick Start: Find a Retrosynthesis Route in a Few Lines"
description: "A minimal, CI-tested working example of RENKIN's find_routes API in Python, Rust, and the CLI, plus how to supply a custom building-block stock."
---

# Quick Start

## Python

```python
--8<-- "examples/quickstart.py"
```

Output, captured from an actual run of the example above (CI executes the
example on every change to confirm it still runs without error, but does not
diff its output against the text below):
```
Routes found: 3
Route (depth 1):
  OC(=O)c1ccccc1OC(=O)C -> O=CC + c1cccc(c1O)C(O)=O
  via co_aliphatic_cleavage
Route (depth 1):
  OC(=O)c1ccccc1OC(=O)C -> OC(=O)C + c1cccc(c1O)C(O)=O
  via ester_cleavage
Route (depth 1):
  OC(=O)c1ccccc1OC(=O)C -> c1cccc(c1O)C(O)=O + OC(=O)C
  via aryl_ether_retro
```

`find_routes` returns a **JSON string** — always `json.loads()` it before
accessing fields; see [Python API](../api/python.md) for the full parameter
list (custom templates, evidence metadata, constraints, pricing, etc.).

## Custom Building Blocks

You can supply your own building block library:

```python
import renkin, json

my_stock = [
    "CC(=O)O",       # acetic acid
    "Oc1ccccc1",     # phenol
    "c1ccccc1",      # benzene
    "Brc1ccccc1",    # bromobenzene
    "OB(O)c1ccccc1", # phenylboronic acid
]

result = json.loads(renkin.find_routes(
    target="c1ccc(-c2ccccc2)cc1",  # biphenyl
    building_blocks=my_stock,
    depth=3,
))
print(f"Routes found: {result['routes_found']}")
# Routes found: 1 (bromobenzene + benzene via suzuki_retro, the only rule
# this small 5-compound stock can support)
```

## Rust

```rust
--8<-- "examples/quickstart.rs"
```

`find_routes` returns `Result<(Vec<Route>, SearchStats)>` — destructure the
tuple, and note `route.depth`/`route.steps` are plain fields, not methods. See
[Rust API](../api/rust.md) for the full signature and `SearchConfig` fields.

## CLI Benchmark

```bash
# Run retrosynthesis on a list of targets
renkin-bench \
    --input targets.smi \
    --building-blocks data/building_blocks.smi \
    --depth 3 \
    --beam-width 50 \
    > results.json
```

The input file should be a SMILES file (one SMILES per line, optional name after whitespace).

## SMILES File Format

Building blocks and target files use the standard `.smi` format:

```
CC(=O)O         acetic_acid
c1ccccc1        benzene
# Comments start with #
Brc1ccccc1      bromobenzene
```
