> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tokenlab.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Error Handling

> Handle API errors gracefully

## Error Response Format

All errors return a consistent JSON format with optional [Agent-First hints](/guides/agent-first-api):

```json theme={null}
{
  "error": {
    "message": "Human-readable error description",
    "type": "error_type",
    "code": "error_code",
    "param": "parameter_name",
    "did_you_mean": "suggested_model",
    "suggestions": [{"id": "model-id"}],
    "hint": "Next step guidance",
    "retryable": true,
    "retry_after": 30
  }
}
```

The required base fields (`message`, `type`) are always present. `code` and `param` are optional and appear only when relevant. The hint fields (`did_you_mean`, `suggestions`, `hint`, `retryable`, `retry_after`, `balance_usd`, `estimated_cost_usd`) are optional extensions for AI agent self-correction. See the [Agent-First API guide](/guides/agent-first-api) for details.

OpenAI-compatible endpoints use TokenLab's stable gateway error types. Anthropic-compatible and Gemini-compatible endpoints use their own native error families and response shapes.

## HTTP Status Codes

| Code | Description                                           |
| ---- | ----------------------------------------------------- |
| 400  | Bad Request - Invalid parameters                      |
| 401  | Unauthorized - Invalid or missing API key             |
| 402  | Payment Required - Insufficient balance               |
| 403  | Forbidden - Access denied or model not allowed        |
| 404  | Not Found - Model or resource not found               |
| 413  | Payload Too Large - Input or file size exceeded       |
| 429  | Too Many Requests - Rate limit exceeded               |
| 500  | Internal Server Error                                 |
| 502  | Bad Gateway - Upstream provider error                 |
| 503  | Service Unavailable - Service temporarily unavailable |
| 504  | Gateway Timeout - Request timed out                   |

## Error Types

### Authentication Errors (401)

| Type              | Code              | Description                   |
| ----------------- | ----------------- | ----------------------------- |
| `invalid_api_key` | `invalid_api_key` | API key is missing or invalid |
| `expired_api_key` | `expired_api_key` | API key has been revoked      |

```python theme={null}
from openai import OpenAI, AuthenticationError

try:
    response = client.chat.completions.create(...)
except AuthenticationError as e:
    print(f"Authentication failed: {e.message}")
```

### Payment Errors (402)

| Type                   | Code                   | Description                 |
| ---------------------- | ---------------------- | --------------------------- |
| `insufficient_balance` | `insufficient_balance` | Account balance is too low  |
| `quota_exceeded`       | `quota_exceeded`       | API key usage limit reached |

```python theme={null}
from openai import OpenAI, APIStatusError

try:
    response = client.chat.completions.create(...)
except APIStatusError as e:
    if e.status_code == 402:
        print("Please top up your account balance")
```

### Access Errors (403)

| Type            | Code                | Description                        |
| --------------- | ------------------- | ---------------------------------- |
| `access_denied` | `access_denied`     | Access to resource denied          |
| `access_denied` | `model_not_allowed` | Model not allowed for this API key |

```json theme={null}
{
  "error": {
    "message": "You don't have permission to access this model",
    "type": "access_denied",
    "code": "model_not_allowed"
  }
}
```

### Validation Errors (400)

| Type                      | Description                                                   |
| ------------------------- | ------------------------------------------------------------- |
| `invalid_request_error`   | Request parameters are invalid                                |
| `context_length_exceeded` | Input too long for model                                      |
| `model_not_found`         | Requested model is not available in the current model details |

```json theme={null}
{
  "error": {
    "message": "Model not found: please check the model name",
    "type": "invalid_request_error",
    "param": "model",
    "code": "model_not_found",
    "did_you_mean": "gpt-5.4",
    "suggestions": [{"id": "gpt-5.4"}, {"id": "gpt-5-mini"}],
    "hint": "Did you mean 'gpt-5.4'? Use GET https://api.tokenlab.sh/v1/models to list all available models."
  }
}
```

Public routes do not distinguish typo, hidden, deferred, or non-public model states in the response body. If a model is not currently available through the model details, TokenLab returns `model_not_found`.

### Rate Limit Errors (429)

When you exceed rate limits:

```json theme={null}
{
  "error": {
    "message": "Rate limit: 1000 rpm exceeded",
    "type": "rate_limit_exceeded",
    "code": "rate_limit_exceeded",
    "retryable": true,
    "retry_after": 8,
    "hint": "Rate limited. Retry after 8s. Current limit: 1000/min for user role."
  }
}
```

**Headers included:**

```
Retry-After: 8
```

The `Retry-After` header and `retry_after` field both indicate the exact seconds to wait before retrying.

### Payload Too Large (413)

When input or file size exceeds limits:

```json theme={null}
{
  "error": {
    "message": "Input size exceeds maximum allowed",
    "type": "invalid_request_error",
    "code": "payload_too_large"
  }
}
```

Common causes:

* Image file too large (max 20MB)
* Audio file too large (max 25MB)
* Input text exceeds model context length

### Upstream Errors (502, 503)

| Type                  | Description                |
| --------------------- | -------------------------- |
| `upstream_error`      | Provider returned an error |
| `all_channels_failed` | No available providers     |
| `timeout_error`       | Request timed out          |

When all channels fail, the response includes alternative models:

```json theme={null}
{
  "error": {
    "message": "Model claude-opus-4-6 temporarily unavailable",
    "code": "all_channels_failed",
    "retryable": true,
    "retry_after": 30,
    "alternatives": [
      {"id": "claude-sonnet-4-6", "status": "available", "tags": []},
      {"id": "gpt-5-mini", "status": "available", "tags": []}
    ],
    "hint": "Retry in 30s or switch to an available model."
  }
}
```

## Handling Errors in Python

```python theme={null}
from openai import OpenAI, APIError, RateLimitError, APIConnectionError

client = OpenAI(
    api_key="sk-your-api-key",
    base_url="https://api.tokenlab.sh/v1"
)

def chat_with_retry(messages, max_retries=3):
    for attempt in range(max_retries):
        try:
            return client.chat.completions.create(
                model="gpt-4o",
                messages=messages
            )
        except RateLimitError as e:
            if attempt < max_retries - 1:
                import time
                time.sleep(2 ** attempt)  # Exponential backoff
                continue
            raise
        except APIConnectionError as e:
            print(f"Connection error: {e}")
            raise
        except APIError as e:
            print(f"API error: {e.status_code} - {e.message}")
            raise
```

## Handling Errors in JavaScript

```javascript theme={null}
import OpenAI from 'openai';

const client = new OpenAI({
  apiKey: 'sk-your-api-key',
  baseURL: 'https://api.tokenlab.sh/v1'
});

async function chatWithRetry(messages, maxRetries = 3) {
  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      return await client.chat.completions.create({
        model: 'gpt-4o',
        messages
      });
    } catch (error) {
      if (error instanceof OpenAI.RateLimitError) {
        if (attempt < maxRetries - 1) {
          await new Promise(r => setTimeout(r, 2 ** attempt * 1000));
          continue;
        }
      }
      throw error;
    }
  }
}
```

## Best Practices

<AccordionGroup>
  <Accordion title="Implement exponential backoff">
    When rate limited, wait progressively longer between retries:

    ```python theme={null}
    wait_time = 2 ** attempt  # 1s, 2s, 4s, 8s...
    ```
  </Accordion>

  <Accordion title="Set timeouts">
    Always set reasonable timeouts to avoid hanging requests:

    ```python theme={null}
    client = OpenAI(timeout=60.0)  # 60 second timeout
    ```
  </Accordion>

  <Accordion title="Log errors for debugging">
    Log the full error response including request ID for support:

    ```python theme={null}
    except APIError as e:
        logger.error(f"API Error: {e.status_code} - {e.message}")
    ```
  </Accordion>

  <Accordion title="Handle model-specific errors">
    Some models have specific requirements (e.g., max tokens, image formats).
    Validate inputs before making requests.
  </Accordion>
</AccordionGroup>