FIVE Character Engine
Keep NPCs, coaches, and branded personas on-script in agent-built apps using FIVE’s constraint engine over MCP.
Overview
FIVE Character Engine MCP is a MCP server for the Build phase that enforces LLM character consistency using large-scale deductive JSON constraints.
What is this MCP server?
- 160K deductive JSON constraints to reduce persona drift in long conversations
- FIVE Character Engine exposed as PyPI stdio MCP package five-mcp v0.1.3
- Requires FIVE_API_KEY (five_sk_xxx) from fiveengine.dev
- Targets character consistency for games, coaching bots, and branded assistants
- Enforces structured persona rules instead of ad-hoc system prompt tweaks
- Advertises 160K deductive JSON constraints
- Package version 0.1.3 on PyPI (five-mcp)
- Requires FIVE_API_KEY environment variable
What problem does it solve?
Custom personas slowly drift from canon, breaking user trust in character-driven apps and support bots.
Who is it for?
Indie builders creating character-heavy agents, RPG dialogue, or branded assistants who need structured persona enforcement.
Skip if: Simple single-turn chat widgets with no ongoing character identity requirements.
What do I get? / Deliverables
After install, your agent can apply FIVE constraints so characters stay aligned with defined persona JSON across builds and tests.
- MCP-backed access to FIVE character constraint tooling
- Reduced persona drift in agent-integrated character features
- Documented env wiring for FIVE_API_KEY in local dev
Recommended MCP Servers
Journey fit
How it compares
Dedicated character-consistency MCP, not a general LLM routing or RAG server.
Common Questions / FAQ
Who is FIVE Character Engine MCP for?
Solo developers building games, coaching apps, or branded AI characters who need stable persona behavior inside agent-assisted development.
When should I use FIVE Character Engine MCP?
Use it during Build agent-tooling when dialogue, NPCs, or coaches must obey a formal character spec and you see drift in prototypes.
How do I add FIVE Character Engine MCP to my agent?
Install the five-mcp PyPI package for stdio MCP, set environment variable FIVE_API_KEY to your five_sk_xxx key from https://fiveengine.dev, and add the server in your MCP config.