# Troubleshoot by Symptom: z-request-id Pinpoints 401 / 502 / Broken Streams

> AI gateway troubleshooting: z-request-id traces 401 / 403 / 404 / 502 / 503 / timeout / broken stream / OOM end to end, error-code normalization, no stream buffering. Triage by symptom, not by guess.

Canonical: https://www.gatellm.io/use-cases/troubleshooting/

Trace 401 / 403 / 404 / 502 / 503 / timeout / broken stream / OOM by z-request-id end to end — no more guessing.

## What the community actually complains about
High-frequency StackOverflow questions: "streaming response turned into one blob after the proxy," "tool-calling JSON won't assemble," "is this 429 rate-limit or quota-exceeded," "is this 502 the gateway or the vendor."
AI-call troubleshooting is hard: multi-hop paths, streaming, inconsistent error codes — when something breaks you don't know which hop.

## How GateLLM does it
GateLLM assigns each request a z-request-id that threads through the whole log, so you locate by symptom: 401 / 403 → auth and Header ACL; 404 → routing; 502 / 503 → upstream health; timeout → rate limit and cross-ocean; broken stream → buffering and SSE; OOM → config.
Error codes are normalized (cross-vendor error semantics unified), streaming passes through natively without buffering, and Token Ops logs are queryable and exportable.

## 5 levers that actually land
- z-request-id threads through the whole log — locate by id in one step
- Triage by symptom: 401 / 403 / 404 / 502 / 503 / timeout / broken stream / OOM
- Error-code normalization: cross-vendor error semantics unified to one vocabulary
- Native stream pass-through, no buffering, no breaking SSE or tool calling
- Token Ops logs queryable and exportable, wired into troubleshooting and reconciliation

## FAQ
### AI gateway streaming response stops streaming after the proxy?
A poor proxy buffers the stream. GateLLM passes streams through natively without buffering and does capability normalization, never breaking SSE or tool calling.

### How do I tell a rate-limit 429 from a quota-exceeded 429?
z-request-id end-to-end tracing plus error-code normalization distinguish rate-limit 429 from quota-exceeded 429 — triage by symptom instead of guessing.

- [Full how-to: Troubleshoot by symptom (docs)](https://docs.gatellm.io/en/usecases/troubleshooting)

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