llm-cache-proxy

One env var. 60–80% cheaper dev loops. A localhost proxy that caches identical OpenAI and Anthropic API calls on disk and replays them for free. Works with every existing tool.

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Why

You're iterating on a prompt. You run the same call 40 times tweaking wording. That's 40× the spend on identical requests.

Or: you have a long-running script that re-fetches the same tool definitions every run during development. Or: your test suite calls the API.

llm-cache-proxy sits on localhost, speaks the OpenAI and Anthropic REST protocols, and caches every successful response in a single SQLite file. Identical requests (same method, path, body) get served from disk — no network call, no spend.

It works with every tool because you only change one env var:

export OPENAI_BASE_URL=http://127.0.0.1:9001/openai/v1
export ANTHROPIC_BASE_URL=http://127.0.0.1:9001/anthropic

Cursor, Claude Code, your scripts, your tests, the OpenAI Python SDK, the Anthropic SDK — they all start using the cache automatically.

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Install & run

pip install llm-cache-proxy
llm-cache-proxy
# or
uvx llm-cache-proxy

Default port: 9001. Default cache: ~/.cache/llm-cache-proxy/cache.db.

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Use it

In whatever shell launches your tool / script:

# OpenAI
export OPENAI_BASE_URL=http://127.0.0.1:9001/openai/v1

# Anthropic
export ANTHROPIC_BASE_URL=http://127.0.0.1:9001/anthropic

# now run anything — Cursor, your script, pytest, etc.

Responses include a X-LLM-Cache: HIT|MISS header so you can see what happened.

Bypass the cache for a single request:

curl -H "x-llm-cache-bypass: 1" http://127.0.0.1:9001/openai/v1/chat/completions ...

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See what you saved

curl http://127.0.0.1:9001/stats

{
  "hits": 312,
  "misses": 87,
  "bytes_served_from_cache": 4_182_404,
  "entries": 87,
  "cached_response_bytes": 1_205_211,
  "by_model": {"gpt-4o": 41, "claude-sonnet-4": 46}
}

Clear the cache:

curl -X DELETE http://127.0.0.1:9001/cache
curl -X DELETE http://127.0.0.1:9001/stats

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Config (all optional)

Env var	Default	Description
LLM_CACHE_PORT	9001	Listen port.
LLM_CACHE_HOST	127.0.0.1	Listen host.
LLM_CACHE_DIR	~/.cache/llm-cache-proxy	Where to put the SQLite file.
LLM_CACHE_TTL	0	TTL in seconds (0 = forever).
LLM_CACHE_TIMEOUT	300	Upstream request timeout.
OPENAI_UPSTREAM	https://api.openai.com	Override the upstream.
ANTHROPIC_UPSTREAM	https://api.anthropic.com	Override the upstream.

Per-request:

• Header x-llm-cache-bypass: 1 — skip both read and write for this call.
• Header x-llm-cache-extra-key: <string> — add an extra dimension to the cache key (e.g., a user id, a session id).

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How the cache key is built

sha256(method + "|" + path + "|" + body + optional extra_key)

Method + path + body is enough to make identical requests collide deterministically. Headers are not included in the default key (so API key rotation doesn't invalidate the cache) — set x-llm-cache-extra-key if you want extra dimensions.

Only 2xx responses are cached. Errors always go through.

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Caveats

• Streaming responses: when the upstream returns text/event-stream, the full SSE body is captured and replayed verbatim on cache hit. That works but you lose per-token streaming feel.
• Tool / function-calling responses cache fine — the whole completion object is one entry.
• Don't expose this proxy to the public internet — it has no auth and your API key flows through it.

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Companion projects

• mcp-rec — VCR for MCP servers (similar idea, MCP layer).
• ai-first-scraper — clean Markdown for LLM agents.

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About the author

Built by yubinkim444, who also makes Kay's Records — an app for iOS and Android.

If this project saved you time, giving the app a try is the nicest way to say thanks.

License

MIT © yubinkim444