I recently faced a major issue where a single request, which should have cost around $0.43, unexpectedly spiked to $7.81 due to a recursive JSON object. This bloated into a massive 3.2MB payload that was sent to the LLM as its 'context'. The problem is that our monitoring system didn't catch this - we saw HTTP 200s all around, token usage seemed reasonable, and our cost alerts were delayed by more than 6 hours. We didn't have any checks for payload sizes either. To tackle this issue, I implemented a few fixes including a hard limit of 100KB at the API boundary, per-request cost tracking with a $3 circuit breaker, schema validation in CI to avoid circular references, and a deduplication script. After these changes, we noticed a 91% drop in duplicate requests and managed to avoid two more costly mistakes before they went to billing. I'm curious if anyone else has implemented similar strategies to validate payloads before they hit expensive APIs?
3 Answers
It sounds like your monitoring needs an overhaul, especially if you’re missing payload size checks. You might want to use a token counter, like OpenAI's, to predict costs accurately before they spike. It could save you a lot of headaches!
Have you considered using serverless functions? They can auto-scale and might help you catch odd processing patterns in real-time. Plus, implementing more immediate logging might provide quicker insights than standard monitoring. Just a thought!
I think the approach you’ve taken is solid, but do make sure to review your overall system design too. Sometimes, the initial setup has design flaws leading to these kinds of blow-ups. A good validation process at the API level is essential.

Totally agree! I’ve found that having a clear view on payload sizes and costs up front really helps catch issues before they become expensive.