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

# Troubleshooting

When a FastEdge application fails, the response includes a FastEdge-specific 5xx status code. The code identifies whether the failure happened during initialization, execution, timeout, or memory allocation.

Start by identifying the returned status code. Then enable debug logging to capture application output and investigate the root cause.

## HTTP error codes

| Code | Meaning                             | Common causes                                                                                                     |
| ---- | ----------------------------------- | ----------------------------------------------------------------------------------------------------------------- |
| 530  | Application initialization failed   | Missing or invalid environment variable, wrong compilation target, corrupt binary                                 |
| 531  | Runtime error — unhandled exception | Rust panic, JavaScript `TypeError`, failed outbound request, unexpected `null`                                    |
| 532  | Execution timed out                 | Handler exceeded the execution time limit; check for infinite loops, expensive processing, or slow outbound calls |
| 533  | Memory limit exceeded               | Application allocated more memory than the plan allows                                                            |

## Debug logging

Production applications do not write logs by default. Enable debug mode before reproducing the issue to capture `console.log` output (JavaScript) or `println!` output (Rust).

Enable debug mode:

```bash theme={null}
curl -X PATCH "https://api.gcore.com/fastedge/v1/apps/{app_id}" \
  -H "Authorization: APIKey $GCORE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"debug": true}'
```

Debug mode stays active for 30 minutes and then turns off automatically. Reproduce the failure, then retrieve the logs:

```bash theme={null}
curl "https://api.gcore.com/fastedge/v1/apps/{app_id}/logs" \
  -H "Authorization: APIKey $GCORE_API_KEY"
```

Available query parameters: `from`, `to`, `edge` (specific PoP), `client_ip`, `request_id`, `search`.

## Platform limits

Exceeding the limits below triggers a 532 (timeout) or 533 (memory) response. Check which plan your application is on if you see these codes repeatedly.

| Resource                | Basic            | Pro               |
| ----------------------- | ---------------- | ----------------- |
| Execution time          | 50 ms            | 200 ms            |
| Memory                  | 128 MB           | 256 MB            |
| Outbound requests       | 5 per invocation | 20 per invocation |
| Request / response body | 1 MB             | 5 MB              |
| Binary size             | \~50 MB          | \~50 MB           |

## Common application issues

### Rust: log output not appearing

`eprintln!` writes to stderr, which FastEdge does not capture. Use `println!` for any output that should appear in debug logs.

### JavaScript: unavailable APIs

The following are not available inside FastEdge JavaScript applications:

* Node.js built-ins: `node:crypto`, `node:fs`, `node:buffer`, `process`, `require`
* `WebSocket`
* Web Cache API — use the [Cache module](/fastedge/cache) (`import { Cache } from 'fastedge::cache'`) instead

## Local testing

Before deploying, test your application locally using the FastEdge CLI. See [FastEdge CLI](/fastedge/fastedge-cli) for installation and full usage.

```bash theme={null}
# Run a Wasm binary as a local HTTP server
fastedge-run http -w ./app.wasm --port 8080

# Launch the visual debugger at http://localhost:3000
fastedge-test
```

For JavaScript applications, `npm run debug` starts the same visual debugger.

## Related resources

| Resource                      | Link                                                                                                 |
| ----------------------------- | ---------------------------------------------------------------------------------------------------- |
| Rust SDK examples             | [github.com/G-Core/FastEdge-sdk-rust/examples](https://github.com/G-Core/FastEdge-sdk-rust/examples) |
| JavaScript SDK examples       | [github.com/G-Core/FastEdge-sdk-js/examples](https://github.com/G-Core/FastEdge-sdk-js/examples)     |
| AssemblyScript SDK examples   | [github.com/G-Core/proxy-wasm-sdk-as/examples](https://github.com/G-Core/proxy-wasm-sdk-as/examples) |
| Rust SDK                      | [github.com/G-Core/FastEdge-sdk-rust](https://github.com/G-Core/FastEdge-sdk-rust)                   |
| Rust API reference            | [docs.rs/fastedge](https://docs.rs/fastedge/latest/fastedge/)                                        |
| JavaScript SDK                | [github.com/G-Core/FastEdge-sdk-js](https://github.com/G-Core/FastEdge-sdk-js)                       |
| JavaScript reference          | [g-core.github.io/FastEdge-sdk-js](https://g-core.github.io/FastEdge-sdk-js/)                        |
| AssemblyScript SDK (CDN apps) | [github.com/G-Core/proxy-wasm-sdk-as](https://github.com/G-Core/proxy-wasm-sdk-as)                   |
| MCP server                    | [github.com/G-Core/FastEdge-mcp-server](https://github.com/G-Core/FastEdge-mcp-server)               |
| VSCode extension              | [github.com/G-Core/FastEdge-vscode](https://github.com/G-Core/FastEdge-vscode)                       |
| FastEdge Test                 | [github.com/G-Core/FastEdge-test](https://github.com/G-Core/FastEdge-test)                           |