Fathom

Fathom is a deterministic reasoning runtime for AI agents, built on CLIPS via clipspy. Rules are authored in YAML, compiled to CLIPS constructs, and evaluated in microseconds with auditable traces.

Current release: fathom-rules 0.3.0 (requires Python 3.14+).

Start here

• Getting Started — install, first template, first rule, first evaluation.
• Tutorial 1 — Hello-world policy — the same material, guided step by step.

Documentation by quadrant

The docs follow the Diátaxis framework. Pick the quadrant that matches what you're doing.

Learn — Tutorials

• Hello-world policy
• Modules and salience
• Working memory across evaluations

Solve a task — How-to Guides

• Writing rules
• Integrating with FastAPI
• Using the CLI
• Registering a Python function
• Loading a rule pack
• Embedding via SDK

Understand — Concepts

• Five Primitives
• Runtime and Working Memory
• YAML Compilation
• Audit and Attestation
• CLIPS Features Not in v1

Look up — Reference

• YAML: Template · Rule · Module · Function · Fact
• APIs: REST · gRPC · MCP Tools
• CLI
• SDKs: Python · Go · TypeScript
• Rule Packs
• Planned Integrations

What is not in v1

Fathom v1 is forward-chaining only and deliberately narrow. Backward chaining, COOL (CLIPS object system), and message handlers are out of scope for this release. See CLIPS Features Not in v1 for the full list and the rationale.