OpenAIError
openai.OpenAIError (fine-tuning validation failure)
Stack trace
openai.OpenAIError: Fine-tuning job failed validation: training file contains invalid JSONL format or missing required fields
at openai.client.fine_tunes.create (openai/api_resources/fine_tunes.py:45)
at main.py:25 Why it happens
OpenAI fine-tuning requires the training file to be in valid JSONL format with each line containing a prompt and completion field. Validation fails if the file is malformed, missing required fields, or if parameters like model or suffix are invalid. This prevents starting a fine-tuning job with bad data.
Detection
Before submitting, validate your JSONL training file with a JSONL linter and check that all required fields (prompt, completion) are present and properly formatted. Catch OpenAIError exceptions and log the detailed validation message.
Causes & fixes
Training file is not valid JSONL or contains malformed JSON lines
Use a JSONL validator tool to ensure each line is a valid JSON object and the file has no trailing commas or syntax errors.
Training data lines missing required 'prompt' or 'completion' fields
Ensure every JSON object in the training file includes both 'prompt' and 'completion' keys with string values.
Specified base model for fine-tuning is invalid or unsupported
Verify the model parameter matches a supported fine-tunable model like 'gpt-4o-mini' or 'gpt-3.5-turbo-0613'.
Training file not uploaded or file ID is incorrect in the fine-tuning request
Upload the training file via the OpenAI files endpoint and use the returned file ID exactly in the fine-tuning job creation call.
Code: broken vs fixed
import os
from openai import OpenAI
client = OpenAI()
# This will fail if training file is invalid
response = client.fine_tunes.create(
training_file="file-invalid-jsonl",
model="gpt-4o-mini"
) # triggers validation error
print(response)import os
from openai import OpenAI
client = OpenAI()
# Fixed: Use valid uploaded file ID and valid model
response = client.fine_tunes.create(
training_file=os.environ["OPENAI_TRAINING_FILE_ID"], # valid uploaded file ID
model="gpt-4o-mini" # valid fine-tunable model
)
print(response) # prints fine-tuning job infoWorkaround
If you cannot fix the training file immediately, catch the OpenAIError exception, parse the error message, and log it for offline inspection while continuing other workflows.
Prevention
Automate validation of your training JSONL files with linters and schema checks before uploading, and always verify file upload success and model compatibility before creating fine-tuning jobs.