> ## Documentation Index
> Fetch the complete documentation index at: https://docs.preprod.world/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

### Request headers missing at the origin

If a CDN application adds or sets a request header and the origin never receives it, check the header name. Headers with the `x-cdn-` or `x-gcdn-` prefixes are reserved for internal CDN use and are stripped before the request reaches the origin. Use a different prefix, such as `x-fastedge` or an application-specific name. The Proxy-Wasm header APIs do not return an error for reserved names.

### 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 the application locally with `fastedge-run`, a local HTTP server for compiled Wasm binaries:

```bash theme={null}
fastedge-run http -w ./app.wasm --port 8080
```

Full `fastedge-run` usage is in [FastEdge CLI](/fastedge/fastedge-cli). Three more tools speed up local development: [Test framework](/fastedge/local-development/test-framework) for headless test suites and a browser debugger, the [FastEdge extension](/fastedge/local-development/vscode-extension) for building and debugging inside VS Code, and [AI-assisted development](/fastedge/local-development/ai-assisted-development) for scaffolding and deploying apps through Claude Code, Codex, or Cursor.

## 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)                   |