Underlay

Underlay is a protocol for giving structured data a permanent address. You push JSON records and a JSON Schema. You get back a versioned, content-addressed snapshot you can point to forever.

Every piece of content — records, schemas, and files — is identified by its SHA-256 hash. Versions are manifests that reference these hashes. Storage is deduplicated globally, transfers only move data the other side doesn't have, and provenance is built in: any record can be traced back to every collection and version that includes it.

Schemas are first-class objects: inspectable, comparable, and alignable across independently authored datasets. Two collections that independently define the same Author type produce the same schema hash — alignment falls out of the data model automatically. The infrastructure doesn't need to solve interoperability. It provides enough structure that interoperability can be solved dynamically by the tools and models that consume the data.

The protocol is simple: push records in, pull records out, trust the versions. The intelligence lives in the actors, not the store. The reference implementation runs at underlay.org.

Built by Knowledge Futures, a 501(c)(3) public charity.

Quick Start

Prerequisites

• Node.js 24+ (LTS)
• Docker and Docker Compose

Development

git clone https://github.com/knowledgefutures/underlay.git
cd underlay
./dev.sh

This starts:

• PostgreSQL 17 on port 5433 (host) → 5432 (container)
• Underlay on port 4100

For team members with SOPS keys, the dev script auto-decrypts .env.local from .env.local.enc. External contributors should run cp .env.test .env.local first.

Without Docker

pnpm install
cp .env.test .env.local
# Edit .env.local with your Postgres and S3 connection strings
pnpm db:migrate
pnpm db:seed
pnpm dev:app

Default Seed User

The seed script creates a "Knowledge Futures" org with sample collections. In production, user accounts are created automatically on first sign-in via KF Auth (OIDC SSO).

Content-Addressed Storage

Everything in Underlay is content-addressed by SHA-256:

• Records are stored as objects in a global record_objects table, keyed by the hash of their canonical JSON ({"id":...,"type":...,"data":...}). The same record in ten collections is stored once.
• Schemas are stored in a global schemas table, keyed by content hash. Two collections that define the same type share the same schema row.
• Files are stored in S3, keyed by SHA-256 of their bytes.
• Versions are manifests — join tables (version_records, version_schemas, version_files) that reference content by hash. Creating a new version that shares 99% of its records with the previous version adds only the new records to storage.

This architecture enables hash negotiation for push and pull (only transfer what the other side doesn't have), provenance (which collections contain this exact record), and forking (copy the manifest, not the data).

CLI

The CLI wraps the same versioning logic as the server: hashing, diffing, semver derivation. Versions exist locally in a .underlay/ directory. You can commit multiple times before pushing, inspect history offline, and push when ready.

pnpm cli init my-collection
pnpm cli schema-set schema.json
pnpm cli add records.jsonl
pnpm cli status
pnpm cli commit -m "initial load"
pnpm cli remote add origin https://underlay.org -t ul_mykey -c my-org/my-collection
pnpm cli push

The CLI source lives in src/cli/. For npm distribution, packages/cli/ is a thin publish wrapper that uses esbuild to bundle into a standalone @underlay/cli package.

Local store format

.underlay/
  config.json               # remotes (url, token, collection)
  HEAD                      # current version semver (e.g. v1.2.0)
  objects/ab/cd/abcd1234... # record content, keyed by hash
  schemas/ef/01/ef012345... # schema JSON, keyed by hash
  versions/v1.0.0.json      # version manifest (schemas, records, files, semver)
  staging/records.jsonl     # staged records before commit
  staging/schema.json       # staged schema before commit

Architecture

Layer	Technology
Server	Hono 4 + @hono/node-server
Frontend	React 19 + React Router v7 (SSR + client hydration)
Styling	Tailwind CSS 4 (@tailwindcss/vite)
Build	Vite 6 (client + SSR bundles)
Database	PostgreSQL 17 + Drizzle ORM
File Storage	S3-compatible (Cloudflare R2 in production)
Auth	KF Auth SSO (OIDC) for web sessions + API keys (programmatic)
Deployment	Docker Swarm on Hetzner, Caddy reverse proxy, Cloudflare DNS
CI/CD	GitHub Actions → GHCR → SSH → docker stack deploy
Secrets	SOPS + age encryption

The app runs as a single Hono server on one port (default 3000). In dev, Vite runs in middleware mode for HMR. In production, Vite builds client and SSR bundles that Hono serves directly.

Project Structure

server.ts                 # Hono entry point (API routes + SSR)
vite.config.ts            # Vite config (React, Tailwind, SSR)
src/
├── entry-client.tsx      # Client hydration entry
├── entry-server.tsx      # SSR rendering (renderToPipeableStream)
├── App.tsx               # React Router routes (filesystem-based)
├── route-gen.ts          # Filesystem → route pattern conversion (wires *.data.ts loaders)
├── global.css            # Tailwind theme
├── api/                  # API route handlers
│   ├── auth.server.ts    # API auth middleware (API keys, internal tokens)
│   ├── rate-limit.server.ts # Global API rate limiting (60/min anon, 5k/min authed)
│   ├── accounts.ts       # Account/org profiles, members, avatars
│   ├── agent.ts          # Agent share page (token-authenticated HTML instructions)
│   ├── collections.ts    # Collection CRUD + export, transfer, fork
│   ├── discussion.ts     # Page-anchored discussion threads
│   ├── versions.ts       # Version read APIs (manifest, records, diff) + privacy filtering
│   ├── negotiate.ts      # Push protocol: hash negotiation, record upload, commit
│   ├── records.ts        # Provenance + batch record fetch
│   ├── files.ts          # Content-addressed file storage
│   ├── schemas.ts        # Schema discovery, search, labeling
│   ├── query.ts          # SQL query tool (SQLite export + LLM SQL generation)
│   ├── ark.ts            # ARK identifier management
│   ├── ark-middleware.server.ts # ARK resolution middleware
│   ├── kf-summary.ts     # Internal summary endpoint for KF dashboards
│   ├── admin.ts          # Admin endpoints (mirror mode)
│   └── health.ts         # Health check
├── db/
│   ├── schema.ts         # Drizzle table definitions
│   ├── client.server.ts  # Database client
│   ├── migrate.ts        # Migration runner
│   ├── seed.ts           # Seed data
│   └── migrations/       # Generated SQL migrations
├── lib/
│   ├── core/             # Pure functions shared by server and CLI (each with *.test.ts)
│   │   ├── hash.ts       # hashRecord, hashSchema (SHA-256)
│   │   ├── semver.ts     # deriveSemver
│   │   ├── version-hash.ts # computeVersionHash, computePublicHash
│   │   ├── privacy.ts    # getPrivateTypes, getPrivateFields, filterRecordData
│   │   ├── validate.ts   # AJV schema validation
│   │   ├── types.ts      # Shared type definitions
│   │   └── index.ts      # Re-exports
│   ├── version-helpers.server.ts  # Re-exports core + DB-dependent helpers
│   ├── auth.ts           # better-auth config (KF Auth OIDC, API keys, orgs)
│   ├── auth.server.ts    # Session helpers
│   ├── auth-client.ts    # better-auth React client
│   ├── auth-middleware.ts # React Router requireAuth middleware
│   ├── auth-internal.server.ts # KF Auth internal API client (optional)
│   ├── mirror-config.ts  # Mirror mode config (UNDERLAY_* env vars)
│   ├── mirror-sync.ts    # Server-to-server mirroring
│   ├── sqlite-gen.ts     # Version → SQLite database generation
│   ├── s3.ts             # S3 client
│   └── ark.ts            # ARK identifier utilities
├── cli/                  # CLI source (local versioning + push/pull)
│   ├── cli.ts            # Commander entry point
│   ├── commands/         # init, schema-set, add, status, commit, log, diff, remote, push, pull
│   └── lib/              # Local store, config, staging helpers
├── routes/               # React pages (filesystem routing; sibling *.data.ts = server loaders)
│   ├── index.tsx         # Landing page
│   ├── explore.tsx       # Browse public collections
│   ├── dashboard.tsx     # User's collections
│   ├── protocol.tsx      # Protocol specification
│   ├── query.tsx         # SQL query explorer
│   ├── records/[hash].tsx # Record detail + provenance
│   ├── schemas/          # Schema browser
│   ├── settings/         # Account settings + API keys
│   ├── blog/             # Blog
│   ├── docs/             # Documentation
│   └── [owner]/          # Dynamic owner routes
│       ├── index.tsx
│       ├── settings/     # Org settings
│       │   ├── index.tsx
│       │   ├── members.tsx
│       │   └── keys.tsx
│       └── [collection]/
│           ├── index.tsx
│           ├── versions.tsx
│           ├── schemas.tsx
│           ├── v/[n].tsx
│           ├── diff.tsx
│           └── settings.tsx
├── components/           # Shared React components
packages/
└── cli/                  # npm publish wrapper (@underlay/cli)
    └── package.json      # esbuild bundles src/cli → dist/cli.js
public/
├── llms.txt              # Machine-readable API docs for LLMs
tools/
├── backupDb.ts           # Postgres backup → S3
├── restore.ts            # Restore database from an S3 backup
├── pruneBackups.ts       # Retention pruning of old backups
├── cleanupSessions.ts    # Prune expired negotiate sessions
├── seedMirror.ts         # Minimal seed for mirror instances
└── cron.ts               # Scheduled task runner (backup, prune, mirror sync)

Protocol and Documentation

The protocol and the platform are documented together:

Resource	URL	Purpose
Protocol spec	/protocol	Full protocol: data model, hashing, push, pull, provenance, privacy
User docs	/docs	Concepts, integration guide, API reference, quickstart
llms.txt	/llms.txt	Machine-readable API docs for LLMs and bots

Key API endpoints

All pushes use the negotiate protocol — a three-step flow similar to git's pack negotiation:

Endpoint	Purpose
POST .../versions/negotiate	Start a push session (server returns which hashes it needs)
POST .../versions/negotiate/:sessionId/records	Send only the needed records (NDJSON)
POST .../versions/negotiate/:sessionId/commit	Validate, hash, and create the immutable version
GET .../versions/:semver/manifest	Version manifest (add ?since= for delta)
GET .../versions/:semver/records	Paginated records
GET .../versions/:semver/diff?from=...	Diff between two versions
POST /api/records/batch	Fetch records by hash (JSONL stream)
GET /api/records/:hash/provenance	Find all collections containing a record
POST .../fork	Fork a collection (copies manifest, not data)
GET /api/schemas	Search schemas across all collections

Privacy

Privacy is part of the protocol, not just a hosted-instance feature. It operates at three levels:

• Private types: "private": true on a schema root hides all records of that type from public readers.
• Private fields: "private": true on a schema property strips that field from public responses.
• Private records: "private": true on a record when pushing hides that specific record.

The private flag is not part of the record hash — a record's content identity doesn't change when you change who can see it. Each version has two hashes: a private hash (all content, used by owners for integrity) and a public hash (excludes private types, fields, and records, verifiable by anyone).

Privacy filtering is implemented in src/lib/core/privacy.ts (pure functions) and enforced at the API layer in src/api/versions.ts.

Schema System

Underlay uses globally deduplicated, content-addressed schemas for record validation and interoperability.

• Each record type in a collection has its own JSON Schema, stored as an immutable, content-addressed row in the global schemas table.
• A version declares its full set of type-to-schema bindings via the version_schemas join table.
• If two collections define the same fields and types for a record type, they produce the same schema hash. Alignment is automatic.
• Schemas are never modified. Evolving a type produces a new hash and a new row.

Push payload (negotiate)

{
  "base_version": null,
  "schemas": {
    "Author": { "type": "object", "properties": { "name": { "type": "string" } } },
    "Pub": {
      "type": "object",
      "properties": {
        "title": { "type": "string" },
        "authorId": { "type": "string", "x-ref-type": "Author" }
      }
    }
  },
  "manifest": [{ "id": "auth-1", "type": "Author", "hash": "abc123..." }]
}

The server replies with the record hashes it doesn't have; the client streams just those records (NDJSON) and commits.

Relationship annotations

Fields that hold record IDs of another type use "x-ref-type": "TypeName" to document the relationship. This enables linked-record navigation in the UI and helps LLMs understand the relational graph.

Schema labeling

Schemas can be labeled post-hoc with human-readable names or URIs (e.g. schema.org/Person, dc.author.v1). Labels enable discovery across collections without upfront coordination.

• POST /api/schemas/:id/labels - Add a label
• DELETE /api/schemas/:id/labels/:label - Remove a label
• GET /api/schemas?label=... - Search by label
• Labels are injected as x-underlay-labels in schema exports (opt-out via ?raw=true)

Versioning semantics

• Major bump: Schema set changed (type added, removed, or schema modified)
• Minor bump: Records changed, schema set identical
• Patch bump: Only metadata changed (readme, message)

Deployment

Infrastructure

• Hetzner - Single box (8 vCPU, 16GB RAM) running Docker Swarm
• Caddy - Host-level reverse proxy, TLS via tls internal (Cloudflare Full mode)
• Cloudflare - DNS + CDN + DDoS protection
• R2 - Object storage (zero egress fees), single bucket with prefixes:
  • files/ - Content-addressed immutable uploads
  • _backups/ - Compressed Postgres dumps

Stacks

Two Docker Swarm stacks run on the same box:

Stack	Domain	Host Port	Purpose
underlay-prod	www.underlay.org	3001	Production
underlay-dev	dev.underlay.org	3000	Staging

Container-internal port is always 3000. Host port is configured via PORT in .env files.

CI/CD Flow

1. Push to main → deploys to dev.underlay.org
2. Create a release/tag → deploys to www.underlay.org
3. Manual dispatch → choose environment

The workflow: build Docker image → push to GHCR → decrypt env file for DEPLOY_HOST → SSH to server → docker stack deploy → wait for healthy rollout.

Required GitHub secrets: SSH_PRIVATE_KEY, SSH_USER, GHCR_USER, GHCR_TOKEN, SOPS_AGE_SECRET_KEY.

Docker Compose Files

File	Purpose
docker-compose.yml	Deployed stacks (prod & dev via Swarm)
docker-compose.local.yml	Local development (source-mounted, hot reload)
docker-compose.withauth.yml	Self-hosted: app + KF Auth + MinIO + Caddy

Self-Hosting

Run the Underlay with a bundled auth server (no external auth provider needed):

DOMAIN=https://my-instance.com docker compose -f docker-compose.withauth.yml up -d

This starts Postgres, KF Auth (auth + account), MinIO (S3-compatible storage), the Underlay app, and Caddy with automatic TLS. On first boot, an init container auto-generates all secrets (session keys, OAuth client credentials, S3 credentials).

Optional configuration (via environment variables or .env file):

• SMTP_* vars for email delivery (password resets, invitations)
• GITHUB_CLIENT_ID/GITHUB_CLIENT_SECRET for GitHub login
• GOOGLE_CLIENT_ID/GOOGLE_CLIENT_SECRET for Google login
• ORCID_CLIENT_ID/ORCID_CLIENT_SECRET for ORCID login

To use external S3 (AWS, Cloudflare R2, etc.) instead of bundled MinIO, remove the minio and minio-init services and set S3_BUCKET, S3_REGION, S3_ENDPOINT, S3_ACCESS_KEY, S3_SECRET_KEY in the app environment.

Supporting files live in selfhost/ (Caddyfile, Postgres init script). See /docs/self-host for full details.

Environment Variables

Core

Variable	Description
DATABASE_URL	PostgreSQL connection string
SESSION_SECRET	Secret for signing session cookies (required in production — the app throws at startup without it)
PORT	Server port (default: 3000)
APP_URL	Public base URL of this instance (default: http://localhost:4100)

S3 storage

Variable	Description
S3_BUCKET	S3 bucket name
S3_REGION	S3 region (auto for R2)
S3_ENDPOINT	S3 endpoint URL
S3_ACCESS_KEY	S3 access key
S3_SECRET_KEY	S3 secret key
ASSETS_BASE_URL	Public base URL for uploaded assets like avatars (optional, default: https://assets.underlay.org)

Auth (KF Auth OIDC)

Variable	Description
OIDC_ISSUER_URL	KF Auth issuer URL
OIDC_ISSUER_INTERNAL_URL	Issuer URL for server-to-server calls (optional, defaults to OIDC_ISSUER_URL)
OIDC_CLIENT_ID	OAuth client ID (default: kf_underlay)
OIDC_CLIENT_SECRET	OAuth client secret
OIDC_ACCOUNT_URL	KF Account UI URL (account management links)
AUTH_INTERNAL_API_KEY	Key for KF Auth's internal API (optional; also authenticates /api/kf/summary)
AUTH_INTERNAL_API_URL	KF Auth internal API base URL (optional, defaults to OIDC_ISSUER_INTERNAL_URL)
INTERNAL_API_TOKEN	Legacy x-internal-token for internal service calls (optional)

Optional features

Variable	Description
ARK_DEFAULT_NAAN	Default NAAN for ARK identifiers
CF_ACCOUNT_ID	Cloudflare account ID for LLM-powered natural-language SQL (optional)
CF_API_TOKEN	Cloudflare API token for LLM-powered natural-language SQL (optional)
UNDERLAY_MODE	origin (default) or mirror — read-only mirror of an upstream instance
UNDERLAY_NODE_NAME	Display name for this mirror node
UNDERLAY_UPSTREAM	Upstream Underlay URL to mirror from
UNDERLAY_UPSTREAM_API_KEY	API key for the upstream instance
UNDERLAY_SYNC_SCHEDULE	Cron schedule for mirror sync (default: 0 0 * * 0)
MIRROR_ADMIN_EMAILS	Comma-separated emails allowed to use the mirror admin UI/API
CORS_ORIGINS	Extra allowed CORS origins, comma-separated (APP_URL is always allowed)
MAX_FILE_UPLOAD_BYTES	Max file upload size in bytes (default: 100 MB)

NODE_ENV is set in docker-compose.yml environment: block (not in .env files).

Scripts

# Development
pnpm dev              # Start full local stack (Docker)
pnpm dev:app          # Start server without Docker
pnpm build            # Build for production (client + SSR)
pnpm start            # Start production server
pnpm cli <command>    # Run CLI locally (e.g. pnpm cli init, pnpm cli add)

# Code quality
pnpm typecheck        # TypeScript type checking
pnpm lint             # Lint with oxlint
pnpm fmt              # Format with oxfmt
pnpm fmt:check        # Check formatting
pnpm test             # Run tests (Vitest)
pnpm test:watch       # Run tests in watch mode

# Database
pnpm db:generate      # Generate Drizzle migrations from schema changes
pnpm db:migrate       # Run pending migrations
pnpm db:seed          # Seed database

# Tools
pnpm tool:backup       # Manual database backup to S3
pnpm tool:restore      # List S3 backups; restore one with `-- <s3-key> --yes`
pnpm tool:pruneBackups       # Prune old backups (supports `-- --dry-run`)
pnpm tool:cleanupSessions  # Prune expired negotiate sessions
pnpm tool:seed-mirror      # Seed a mirror instance (admin org only)

# Secrets (SOPS + age)
pnpm secrets:encrypt:local  # Encrypt .env.local → .env.local.enc
pnpm secrets:encrypt:prod   # Encrypt .env.prod → .env.prod.enc
pnpm secrets:encrypt:dev    # Encrypt .env.dev → .env.dev.enc
pnpm secrets:decrypt:local  # Decrypt .env.local.enc → .env.local
pnpm secrets:decrypt:prod   # Decrypt .env.prod.enc → .env.prod
pnpm secrets:decrypt:dev    # Decrypt .env.dev.enc → .env.dev

Maintenance Checklist

When adding or changing features, update these locations:

What	Where	Purpose
Protocol spec	src/routes/protocol.tsx	Protocol documentation page
API documentation	public/llms.txt	Machine-readable docs for LLMs and bots
Concepts	src/routes/docs/concepts.tsx	Core concepts explanation
API reference	src/routes/docs/api/*.tsx	Endpoint-level docs with examples
Integration guide	src/routes/docs/integration.tsx	Developer onboarding guide
Quick start	src/routes/docs/quickstart.tsx	Getting started tutorial
Self-hosting	src/routes/docs/self-host.tsx	Deployment instructions
DB schema	src/db/schema.ts → pnpm db:generate	Schema changes need a migration
Core library	src/lib/core/	Hashing, semver, privacy, validation
CLI commands	src/cli/commands/	Local versioning and sync
Schema discovery	src/api/schemas.ts	Schema search, labeling, cross-referencing
Encrypted secrets	.env.{local,dev,prod}.enc	Re-encrypt after changing .env files

Privacy features

Privacy is part of the protocol. The system supports three levels (type-level, field-level, record-level) via "private": true annotations. When changing how privacy works, update:

• src/lib/core/privacy.ts - pure filtering functions (shared by server and CLI)
• src/api/versions.ts - API-level filtering
• src/api/files.ts - file access checks
• src/api/schemas.ts - public schema filtering
• src/routes/protocol.tsx - protocol spec
• public/llms.txt - Privacy section
• src/routes/docs/concepts.tsx - Privacy section
• src/routes/docs/integration.tsx - Privacy section

License

MIT