# Converting Legacy CTI and XML Input Files to YAML

If you want to convert an existing, legacy CTI or XML input file to the YAML format,
this section will help.

## cti2yaml

Cantera comes with a converter utility `cti2yaml` (or `cti2yaml.py`) that converts
legacy {term}`CTI` format mechanisms into the new YAML format introduced in Cantera 2.5.
This program can be run from the command line to convert files to the YAML format.

**Usage:**

```bash
cti2yaml [-h] input [output]
```

The `input` argument is required, and specifies the name of the input file to be
converted. The optional `output` argument specifies the name of the new output file. If
`output` is not specified, then the output file will have the same name as the input
file, with the extension replaced with `.yaml`. The full command line interface for
`cti2yaml` is documented [here](/yaml/cti2yaml).

**Example:**

```bash
cti2yaml mymech.cti
```

will generate the output file `mymech.yaml`.

If the `cti2yaml` script is not on your path, but the Cantera Python module is,
`cti2yaml` can be used by running:

```bash
python -m cantera.cti2yaml mymech.cti
```

It is not necessary to use `cti2yaml` to convert any of the CTI input files previously
included with Cantera. YAML versions of these files are already included with Cantera.

```{tip}
For input files where you have both the CTI and XML versions, `cti2yaml` is recommended
over `ctml2yaml`. In cases where the mechanism was originally converted from a
{term}`CK`-format mechanism, it is recommended to use `ck2yaml` if the original input
files are available.
```

## ctml2yaml

Cantera comes with a converter utility `ctml2yaml` (or `ctml2yaml.py`) that converts
legacy XML ({term}`CTML`) format mechanisms into the new YAML format introduced in
Cantera 2.5. This program can be run from the command line to convert files to the YAML
format.

**Usage:**

```bash
ctml2yaml [-h] input [output]
```

The `input` argument is required, and specifies the name of the input file to be
converted. The optional `output` argument specifies the name of the new output file. If
`output` is not specified, then the output file will have the same name as the input
file, with the extension replaced with `.yaml`. The full command line interface for
`ctml2yaml` is documented [here](/yaml/ctml2yaml).

**Example:**

```bash
ctml2yaml mymech.xml
```

will generate the output file `mymech.yaml`.

If the `ctml2yaml` script is not on your path, but the Cantera Python module is,
`ctml2yaml` can be used by running:

```bash
python -m cantera.cti2yaml mymech.xml
```

It is not necessary to use `ctml2yaml` to convert any of the XML input files included
with Cantera. YAML versions of these files are already included with Cantera.