Hermes (Open-Weight Model)

Hermes is an open-weight language model tuned specifically to output valid JSON reliably. Unlike frontier models (Claude, GPT-4), Hermes runs locally via llama.cpp or Ollama, which means you get structured data without API latency or per-token costs. The model is trained to follow schema instructions tightly, and when paired with grammar-constrained decoding (a feature in llama.cpp that prevents invalid tokens at generation time), schema violations become structurally impossible. For product teams extracting data from user feedback, operations analysts parsing logs into structured records, or engineers building internal tools that need reliable JSON, Hermes eliminates the "model wrapped JSON in code fences again" failure mode that kills production pipelines. You define a flat JSON schema, provide one example in your prompt, and validate the output locally. The [Tendril guide](https://tendril.neural-forge.io/learn/creators/hermes-structured-json-creators) shows the prompt skeleton and when to use grammar constraints versus plain prompting.

Reliable JSON output from local LLMs without API calls