T1/T2 Protocol

T1/T2 Protocol — Heterogeneous Validation for MCP

中文文档 · MCP Registry entry (io.github.Fauxetine/t1-t2-protocol)

Reference implementation. This is a stdlib-only MCP reference server for structured reasoning discipline — not a production security product. Evaluate your own threat model before deploying in sensitive environments. Unlike official Python MCP servers, it does not use the mcp SDK; it speaks JSON-RPC over stdio directly.

T1/T2 is an MCP server that makes AI reasoning verifiable, auditable, and trustworthy — by decomposing ambiguous questions into structured tiers (T1), then validating answers through cross-model evaluation (T2), with a deterministic checksum layer that doesn't depend on any LLM.

Why?

When an LLM checks its own answer, it uses the same training data, the same reasoning preferences, and the same systematic biases. Self-reflection cannot catch its own blind spots.

T1/T2 introduces heterogeneous validation: the model that produces the answer and the model that evaluates it should be different. Their different training distributions cover each other's blind spots.

Tools

Tool	Function	Why it matters
t1_protocol	Decomposes ambiguous questions into L1 (facts) / L2 (assumptions) / L3 (hypotheses) / L4 (unknowns)	Forces structured reasoning before answering
t2_protocol	Evaluates answer quality from another model's perspective (qualitative five-level confidence)	Catches blind spots self-reflection misses
checksum	Deterministic structural validation — pure regex, zero LLM dependency	Safety that doesn't scale with intelligence

How tools return data: t1_protocol and t2_protocol return structured prompt templates for your MCP host's LLM to execute. Only checksum returns deterministic JSON (checksum_passed, errors).

Tool inputs (MCP schema)

t1_protocol

Input	Type	Required	Description
question	string	yes	The ambiguous question to decompose
locale	string	no	en (default) or zh
weight_hint	string	no	fact-first, efficiency-first, cost-first, robustness-first, general-first (or Chinese equivalents)

t2_protocol

Input	Type	Required	Description
answer	string	yes	Text to evaluate (often the host LLM's draft answer)
locale	string	no	en (default) or zh
weight_hint	string	no	Same values as t1_protocol

checksum

Input	Type	Required	Description
text	string	yes	Structured answer text to validate

Returns JSON: {"checksum_passed": bool, "errors": [...]}.

Quick Start

Requirements

• Python 3.10+
• An MCP client: Cursor, Claude Desktop, Windsurf, or any MCP-compatible host

Install

From PyPI (recommended):

pip install "t1-t2-protocol>=0.1.0"

From source (development):

git clone https://github.com/Fauxetine/t1-t2-protocol.git
cd t1-t2-protocol
pip install -e ".[dev]"
T1T2_DISABLE_COUNTERS=1 python -m pytest tests/ -v

Or run directly without installing:

python src/t1_t2_mcp_server.py   # Windows
python3 src/t1_t2_mcp_server.py  # macOS / Linux

Configure

After pip install, use the console script in MCP config (recommended):

{
  "mcpServers": {
    "t1-t2-protocol": {
      "type": "stdio",
      "command": "t1-t2-protocol"
    }
  }
}

Cursor — .cursor/mcp.json (same as above).

Claude Desktop — claude_desktop_config.json:

{
  "mcpServers": {
    "t1-t2-protocol": {
      "command": "t1-t2-protocol"
    }
  }
}

From source (no pip install) — point at the script:

{
  "mcpServers": {
    "t1-t2-protocol": {
      "type": "stdio",
      "command": "python",
      "args": ["C:/path/to/t1-t2-protocol/src/t1_t2_mcp_server.py"]
    }
  }
}

On macOS/Linux use "command": "python3" instead of "python".

Verify it works

1. Restart or reload your MCP host after editing config.
2. Confirm three tools appear: t1_protocol, t2_protocol, checksum.
3. Call t1_protocol with {"question": "Should we adopt microservices?", "locale": "en"} — you should receive a structured T1 prompt template.
4. Call checksum with sample [L1 Facts] … --- text — you should receive JSON with checksum_passed.

Usage

T1: Structure a vague question

Call t1_protocol with your question. The host LLM receives a structured prompt template with four tiers:

Input:  {"question": "Should we migrate our monolith to microservices?"}

Output: Prompt template instructing the host to produce:
  [L1 Facts]      Team size, codebase size, current stack
  [L2 Assumptions] Expected benefits that need verification
  [L3 Hypotheses] Testable claims about migration risk
  [L4 Unknown]    Future growth trajectory
  [Core Question] The precise feasibility question

T2: Cross-validate a decision

Call t2_protocol with a decision or answer text. Returns an evaluation prompt for the host LLM:

Input:  {"answer": "Decision text for approach A..."}

Output: Prompt template requesting:
  Confidence: high | medium-high | medium | medium-low | low
  Adoption table with:
    ✅ Adopt     — verified conclusions (L1)
    ⚠️ Reserved — needs more evidence (L2)
    ❌ N/A      — blind spots to address

checksum: Validate output structure

Call checksum with structured text. It returns pass/fail based on deterministic rules:

Input: "[L1 Facts]\n1. ...\n[L2 Assumptions]\n1. ...\n---"
Output: {"checksum_passed": true, "errors": []}

Full pipeline

Vague question → T1 structured decomposition → Decision based on structure → checksum (optional) → T2 validation → Refined decision

For time-sensitive factual claims, search on the caller side before T2 — see Caller-side web verification (v2.6).

Configuration

Locale

Both t1_protocol and t2_protocol accept an optional locale parameter:

Value	Output
en (default)	English templates
zh	Chinese templates

Example: {"question": "...", "locale": "zh"}

Weight hints

Both t1_protocol and t2_protocol accept an optional weight_hint parameter to bias evaluation criteria:

Weight	Effect
事实优先 / fact-first	Prioritizes factual accuracy
效率优先 / efficiency-first	Prioritizes efficiency
成本优先 / cost-first	Prioritizes cost
鲁棒性优先 / robustness-first	Prioritizes robustness
通用优先 / general-first	No specific bias

Recursion protection

T2 automatically detects recursion depth and terminates at depth >= 3, where marginal information gain drops below 5%.

Design Philosophy

See docs/philosophy.md for the full design rationale.

Core tenets:

1. Separate intelligence from trust — AI capability and AI safety should be guaranteed by different systems
2. Heterogeneous over self-referential — Cross-model validation is more reliable than self-reflection
3. Deterministic over probabilistic — What can be checked by code should not be left to model judgment

Examples

See examples/ for step-by-step walkthroughs:

• T1: Structure a vague question
• T2: Cross-validate a decision
• Full pipeline: T1 → decision → T2

Positioning

Project	Layer	What it does	T1/T2 relationship
Sequential Thinking (official MCP)	Caller-side chain-of-thought	One model logs iterative steps	Complementary — T1 adds L1–L4 tiers + T2 cross-model review
ThoughtProof / verdict APIs	Server-side verification	APPROVE/DENY/UNCERTAIN with confidence	Complementary — T1/T2 structures reasoning before verdict APIs act
Self-reflection / prompt chains	Same model	Re-reads or re-prompts its own output	Replaced — heterogeneous validation catches shared blind spots
Tool integrity (e.g. Phionyx)	Transport / tool schema	Detects tool poisoning, schema drift	Orthogonal — T1/T2 does not secure tool definitions

T1/T2 is a stdlib reference implementation for MCP Discussion #2574-style reasoning discipline: structure first (T1), cross-validate second (T2), checksum what code can verify. It is not a signed verdict API and not a security scanner.

Versioning

Two version numbers — do not conflate them:

	Example	Meaning
Package (PyPI)	0.1.0	Distribution lifecycle. 0.x = experimental (SemVer, FastAPI policy).
Protocol (spec)	v2.5	T1/T2 tool semantics in server output footer. Caller-side web verify docs use v2.6.

Recommended install: pip install "t1-t2-protocol>=0.1.0". Erroneous PyPI releases 2.5.2–2.5.4 are yanked.

License

Apache License 2.0 — see LICENSE.

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Built for the MCP ecosystem. Part of a broader exploration into AI safety through deterministic architecture.

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Links

• Contributing
• MCP Registry — io.github.Fauxetine/t1-t2-protocol
• Security policy
• Changelog
• Design philosophy
• Caller-side web verification v2.6
• Agent / MCP host instructions