PrismGuard is an open-source firewall for LLM apps. Block prompt injection before it hits your model — every allow/block returns resolution_gate (which rule decided), not a probability score your team argues about in Slack.
Rules-first: pip install prismguard. Optional local ONNX. Apache-2.0. Cold holdout: 14/14 vs LLM Guard 9/14.
Wire at agent entry, RAG chunks, or sidecar. v0.1.6 on PyPI — alpha, feedback welcome.