> Documentation index: [Saleor](/llms.txt) · [This section](/developer/llms.txt)
> Source: https://docs.saleor.io/developer/extending/api/errors

# Errors

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## Key concepts

There are several error types in the GraphQL API and you may come across different ones depending on the operations you are trying to perform. This document describes how to add new error types.

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## Add new error type

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### Step 1: Create new error enum

To create new error codes, add `error_codes.py` in the target module. Inside this module create an enum with wanted error codes.

```python
from enum import Enum

class ExampleErrorCode(Enum):
    ALREADY_EXISTS = "already_exists"
    GRAPHQL_ERROR = "graphql_error"
    INVALID = "invalid"
    NOT_FOUND = "not_found"
    REQUIRED = "required"
    UNIQUE = "unique"
```

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### Step 2: Register newly created error code enum

To differentiate between built-in Django's error codes and the custom ones, add the error class to the `SALEOR_ERROR_CODE_ENUMS` list in `saleor/graphql/core/utils/error_codes.py`.

```python
SALEOR_ERROR_CODE_ENUMS = [
    ExampleErrorCode,
    AccountErrorCode,
    AppErrorCode,
    ...
```

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### Step 3: Add error codes to GraphQL enums

To add error codes to GraphQL enums you should add an entry in `saleor/graphql/core/enums.py`.

```python
ExampleErrorCode = graphene.Enum.from_enum(error_codes.ExampleErrorCode)
```

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### Step 4: Create error class

To allow usage error code in mutation, add error class in `saleor/graphql/core/types/common.py`.

```python
class ExampleError(Error):
    code = ExampleErrorCode(description="The error code.", required=True)
```

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### Step 5: Assign error codes to mutation

To use an new error codes in mutation, add `error_type_class` and `error_type_field` to `Meta` inside mutation.

```python
class ExampleMutation(BaseMutation):
    class Meta:
        error_type_class = ExampleError
        error_type_field = "example_errors"
```

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## Add custom field to an error type

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### Step 1: Add new fields to error class

To return more information inside error, add a new field to target error class in `saleor/graphql/core/types/common.py`.

```python
class ExampleError(Error):
    code = ExampleErrorCode(description="The error code.", required=True)
    example_int_value = graphene.Int(description="Example int value.")
    example_string_value =  graphene.String(description="Example string value.")
```

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### Step 2: Raise error with custom values

To return error with custom values, raise an error in target mutation.

```python
error_params = {
    "example_int_value": 1234,
    "example_string_value": "Example error value",
}
raise ValidationError(
    {
        "example_field": ValidationError(
            message="Example message for debugging",
            code=ExampleErrorCode.EXAMPLE,
            params=error_params,
        )
    }
)
```