ambrook-mcp-guardrail

A deterministic pre-flight ledger validator proof-of-concept. An AI agent's proposed financial write is treated as untrusted input and validated against ledger invariants before it reaches a commit boundary.

Inspired by Ambrook's publicly described combination of hybrid AI + rule-based systems, MCP-based tooling, and a multidimensional general ledger (enterprise / project / location / funding dimensions).

This is an independent proof-of-concept inspired by those publicly documented design principles. It is NOT Ambrook's internal implementation.

The invariant

INVALID TRANSACTION → ZERO LEDGER MUTATION. The commit branch is the only path that mutates the ledger.

Related MCP server: Guardian MCP

How validation works

ledger-rules.ts is a pure, deterministic validator. All errors are collected; if any invariant fails, the entire write is rejected with structured errors ({ code, message }) — no partial writes.

Proof — the actual run

Five simulated agent tool calls (agent-test-suite.ts), all asserted programmatically. No results are hand-written; everything below is generated from execution into results.json.

• 8/8 assertions pass, including: every invalid write changes ledger size by zero, and the final ledger contains only the two valid transactions.

• Deterministic: three consecutive runs produced byte-identical output and an identical results.json.

Run it

npm install
npm run build
npm test

npm test compiles, runs the suite, asserts all invariants, and regenerates results.json — exiting non-zero on any failure.

Structure

ledger-types.ts       domain types (Transaction, ToolCall, ValidationError, …)
ledger-rules.ts       deterministic rules L1–L4
mock-mcp-server.ts    mock MCP boundary: write_transaction + in-memory ledger
agent-test-suite.ts   5 simulated agent writes + 8 assertions → results.json

Limitations

• Mock MCP boundary, in-memory ledger, synthetic transactions — no Ambrook infrastructure was touched.

• No production performance claim, and no claim about how Ambrook actually implements validation.

• Zero runtime dependencies: standard Node.js only, no network, no LLM calls, no API keys.