An MCP server that gives AI agents read-write access to a personal knowledge graph — and pays for itself with Bitcoin Lightning micropayments.
FastMCP server for TheBrain API — AI access to a personal knowledge graph, Tollbooth-monetized
2026-11-09
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The metaphors in this project are drawn with admiration from The Phantom Tollbooth by Norton Juster, illustrated by Jules Feiffer (1961). Milo, Tock, the Tollbooth, Dictionopolis, and Digitopolis are creations of Mr. Juster's extraordinary imagination. We just built the payment infrastructure.
The First City
Every turnpike needs its first city. Before the booths can collect fares and the authority can stamp purchase orders, someone has to build a destination worth driving to.
thebrain-mcp is that city — a FastMCP service deployed on Horizon that bridges AI agents to TheBrain, a personal knowledge graph of 9,000+ interconnected thoughts built over a decade. Every thought, link, attachment, and note operation maps directly to TheBrain's cloud API at api.bra.in.
It's also the proving ground for Tollbooth DPYC™ — the first MCP server where every tool call is metered via Bitcoin Lightning micropayments. Pre-fund, use, top up. No subscriptions, no API keys tied to billing accounts, no fiat payment processors. The novel contribution: an MCP server architecture where the operator monetizes AI agent access through Lightning micropayments without ever pestering the client mid-conversation.
Getting Started
Connecting via Horizon MCP
Connect any MCP-compatible client (Claude Desktop, Cursor, your own agent) to the live endpoint:
https://personal-brain.fastmcp.app/mcp
No configuration needed. Your client connects with OAuth; the connection holds no npub until you prove one into it by answering a Nostr DM (request_npub_proof, then receive_npub_proof). A client that holds your nsec signs each request instead (NIP-98) and needs no DM. Tools then take only npub.
First Connection Walkthrough
session_status — Check your current session state.
Get your patron npub from the dpyc-oracle's how_to_join() tool — this is the npub you registered as a DPYC™ Citizen, your identity for credit operations.
Secure Courier onboarding:
Call request_credential_channel(sender_npub=<patron_npub>, service=<service>) — opens a Secure Courier channel, sends a welcome DM to your Nostr client, and returns the channel's nonce.
Reply via your Nostr client with your credentials in JSON: {"api_key": "...", "brain_id": "..."}
Call receive_credentials(sender_npub=<patron_npub>, service=<service>, nonce=<that nonce>) — vaults your credentials and activates the session.
list_brains → set_active_brain — Select which brain to work with.
brain_query — Start exploring your knowledge graph.
Returning users do not re-run this flow: the session restores from the vault on first use.
Secure Courier
Credentials are delivered via encrypted Nostr DMs — they never appear in the chat window. On first-time relay receipt, the service sends an ncred1... credential card back to the patron via DM for scan-and-paste reuse.
Human in the loop: The patron must consciously approve each credential delivery via their Nostr client. Never auto-poll or auto-retry receive_* calls — each receive_credentials drains the relay destructively (NIP-09 deletion after pickup). Call it exactly once per credential delivery.
Credits Model
Category
Pricing hint
Examples
free
0 sats
session_status, check_balance, check_price
read
1 sat
get_thought, search_thoughts, get_note
write
5 sats
create_thought, create_link, update_thought
heavy
10 sats
brain_query, get_modifications
Actual prices are set dynamically by the operator's pricing model in Neon via api_sats per tool. Auth and balance tools are always free.
Credits are issued as tranches with a tranche_lifetime (TTL). Tranches are consumed FIFO; expired tranches are pruned automatically. Use check_balance to see your balance, active tranches, and usage history. Top up via purchase_credits with Bitcoin Lightning.
Security
Identity is a Nostr keypair — users are identified by an npub (Nostr public key), not an email or username. The nsec (private key) stays with the patron — never shared, never sent to a service.
Identity is on the connection — a client that holds the nsec signs each HTTP request (NIP-98, kind 27235); an OAuth client proves the npub once into its connection by answering a Nostr DM (request_npub_proof → receive_npub_proof). Tools carry no proof argument.
Human in the loop — the patron approves each proof in their Nostr client and chooses how long it lasts, up to 30 days. When it lapses, a fresh request/receive cycle renews it.
Credentials via Secure Courier — TheBrain API keys and brain IDs are delivered via NIP-44 encrypted Nostr DMs, vaulted in Neon Postgres, and never exposed in the chat window.
BrainQuery (BQL)
A Cypher-subset query language purpose-built for TheBrain. Agents and humans express graph operations in the same formalism — full CRUD via MATCH, CREATE, SET, MERGE, and DELETE.
MATCH (n {name: "Projects"})-[:CHILD]->(m) RETURN m
MATCH (n) WHERE n.name =~ "quarterly review" RETURN n
MATCH (p {name: "Ideas"}) CREATE (p)-[:CHILD]->(n {name: "New Concept"})
MATCH (root {name: "Company"})-[:CHILD*1..3]->(d) WHERE d.name CONTAINS "Budget" RETURN d
Variable-length paths, multi-hop chains, compound WHERE with AND/OR/NOT/XOR, similarity search, and property existence checks. Full grammar in BRAINQUERY.md.
Troubleshooting
When a tool call fails, read the response — it tells you what happened and what to do next. Credential lifecycle states are not errors; they are expected situations with clear guidance.
Situation
What to do
proof is required
Call request_npub_proof then receive_npub_proof — a fresh request/receive cycle. The proof lasts as long as the patron chose when approving it (up to 30 days).
Insufficient credit balance
Call purchase_credits to top up.
Cold start / session not ready
Retry in 10-15 seconds.
Credentials not found
Follow the Secure Courier onboarding flow (step 3 above).
Upstream API error
Only if the error explicitly mentions TheBrain API failure. Not a credential or billing issue.
Don't Pester Your Customer: Do NOT ask the patron to re-authenticate or re-do the Courier flow unless the error message specifically says credentials are missing or expired.
To run your own instance, set these environment variables:
Required
Variable
Purpose
TOLLBOOTH_NOSTR_OPERATOR_NSEC
Operator's Nostr secret key -- the single bootstrap key for identity, Secure Courier DMs, and audit signing
This is the only env var the server reads. Certified operators bootstrap their Neon database URL from the Authority via encrypted Nostr DM -- NEON_DATABASE_URL is not read from the environment. The relay set comes from the shared dpyc-community registry, and tranche lifetime and constraints come from the operator's pricing model -- none of them is an env var.
Credentials via Secure Courier (NOT env vars)
All secrets flow through Secure Courier -- they never appear as environment variables:
Note:THEBRAIN_API_KEY is not an environment variable. Patrons deliver their TheBrain API key and brain ID via Secure Courier (encrypted Nostr DM). Only the operator's nsec is configured as an env var.
Tool Surface
The server exposes the standard Tollbooth DPYC™ operator surface via
register_standard_tools() from tollbooth-dpyc,
plus its domain tools. Tools fall into three paths in the DPYC three-actor
topology (Operator / Authority / Oracle):
Payment processing auto-certifies via the Authority (server-to-server OAuth). Secure Courier delivers encrypted credentials via Nostr DMs with automatic credential card (ncred1...) DM-back on first receipt. Oracle community tools route directly to the DPYC™ Oracle — free and unauthenticated.
Architecture
The Tollbooth DPYC™ ecosystem is a three-party protocol spanning three repositories:
thebrain-mcp/
├── src/thebrain_mcp/ # Server source, BQL engine, Tollbooth
├── tests/ # Test suite (465+ tests)
├── fastmcp.json # Horizon deploy entrypoint (src/thebrain_mcp/server.py)
├── pyproject.toml # Package metadata and dependencies
├── BRAINQUERY.md # BQL grammar and reference
├── INSTALL.md / QUICKSTART.md # Local install and setup
├── docs/diagrams/ # Architecture and protocol flow diagrams
├── LICENSE # Apache License 2.0
└── NOTICE # Attribution notice
Prior Art & Attribution
The methods, algorithms, and implementations contained in this repository may represent original work by Lonnie VanZandt, first published on February 16, 2026. This public disclosure establishes prior art under U.S. patent law (35 U.S.C. 102).
All use, reproduction, or derivative work must comply with the Apache License 2.0 included in this repository and must provide proper attribution to the original author per the NOTICE file.
How to Attribute
If you use or build upon this work, please include the following in your documentation or source:
Based on original work by Lonnie VanZandt and Claude.ai
Originally published: February 16, 2026
Source: https://github.com/lonniev/thebrain-mcp
Licensed under Apache License 2.0
Visit the technologist's virtual cafe for Bitcoin advocates and coffee aficionados at stablecoin.myshopify.com.
Patent Notice
The author reserves all rights to seek patent protection for the novel methods and systems described herein. Public disclosure of this work establishes a priority date of February 16, 2026. Under the America Invents Act, the author retains a one-year grace period from the date of first public disclosure to file patent applications.
Note to potential filers: This public repository and its full Git history serve as evidence of prior art. Any patent application covering substantially similar methods filed after the publication date of this repository may be subject to invalidation under 35 U.S.C. 102(a).
DPYC™, Tollbooth DPYC™, and Don't Pester Your Customer™ are trademarks of Lonnie VanZandt. See the TRADEMARKS.md in the dpyc-community repository for usage guidelines.
License
Apache License 2.0 — see LICENSE and NOTICE for details.
Because in the end, the tollbooth was never the destination. It was always just the beginning of the journey.