{"slug": "show-hn-prismcat-local-transparent-proxy-and-debugging-console-for-llm-apis", "title": "Show HN: PrismCat – Local transparent proxy and debugging console for LLM APIs", "summary": "A developer released PrismCat, a self-hosted transparent proxy and debugging console for LLM APIs that logs all requests and responses without sending data to third parties. The tool uses subdomain routing to capture traffic from SDKs like LangChain and OpenAI wrappers, allowing users to inspect streaming data and replay failed requests through an interactive UI.", "body_md": "Hi HN,\n\nI built PrismCat because I got tired of not knowing what LLM SDKs (like LangChain or various OpenAI/Anthropic wrappers) were silently injecting into my prompts behind the scenes. It's often hard to debug why a streaming request froze, or why a function-calling agent returned malformed JSON, without diving deep into SDK code.\n\nPrismCat is a single-binary, self-hosted proxy and UI designed to run silently 24/7 as an LLM \"black box\" logger.\n\nHow it works:\nIt uses subdomain routing to achieve transparent proxying. For example, if you add an upstream named `openai`, PrismCat exposes `[http://openai.localhost:8080](http://openai.localhost:8080)`.\n\nModern operating systems and browsers resolve `*.localhost` to `127.0.0.1` automatically, so you don't even need to edit your `/etc/hosts` file. You just change one line in your code—the `base_url`—and everything gets captured transparently (including Server-Sent Events/streaming).\n\nKey features: - Fully local-first: written in Go, stores data in SQLite, never sends your keys or prompts to a third party. - Interactive Playground: Tweak and replay failed requests in the UI without re-running your scripts. - SSE capture: Captures and reconstructs SSE chunks so you can inspect the raw flow. - Request Override (Opt-in): Intercept and rewrite outgoing requests/headers without code changes.\n\nI'd love to hear your feedback on the implementation (especially the subdomain routing approach) and what features you'd like to see next!\n\nComments URL: [https://news.ycombinator.com/item?id=48279360](https://news.ycombinator.com/item?id=48279360)\n\nPoints: 1\n\n# Comments: 2", "url": "https://wpnews.pro/news/show-hn-prismcat-local-transparent-proxy-and-debugging-console-for-llm-apis", "canonical_source": "https://github.com/paopaoandlingyia/PrismCat", "published_at": "2026-05-26 13:11:26+00:00", "updated_at": "2026-05-26 13:41:10.980032+00:00", "lang": "en", "topics": ["ai-tools", "ai-infrastructure", "large-language-models", "ai-products", "ai-agents"], "entities": ["PrismCat", "LangChain", "OpenAI", "Anthropic", "Go", "SQLite"], "alternates": {"html": "https://wpnews.pro/news/show-hn-prismcat-local-transparent-proxy-and-debugging-console-for-llm-apis", "markdown": "https://wpnews.pro/news/show-hn-prismcat-local-transparent-proxy-and-debugging-console-for-llm-apis.md", "text": "https://wpnews.pro/news/show-hn-prismcat-local-transparent-proxy-and-debugging-console-for-llm-apis.txt", "jsonld": "https://wpnews.pro/news/show-hn-prismcat-local-transparent-proxy-and-debugging-console-for-llm-apis.jsonld"}}