Purple Sparrow

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Why

Generic backends were built for humans clicking dashboards. Coding agents operate through APIs — and generic backends fail them in three ways: they fail silently, they leak data through missing access rules, and they're undiscoverable. Purple Sparrow is designed so an agent can drive it correctly and recover on its own.

🛡️ Secure by default	Access is deny-by-default. An app-layer policy engine compiles rules into parameterized SQL with USING and WITH CHECK. Fuzz-tested; the compiler never emits a raw literal.
🧭 Self-correcting	Every error carries machine-readable remediation + next_actions. When an agent hits a wall, the response tells it how to get past it.
🔎 Discoverable	GET /meta returns the whole backend's shape in one call. Docs are served over the API. An advisor lints the config.
🪶 Runs anywhere	One static binary + embedded SQLite — zero dependencies for a solo dev. Point PS_DATABASE_URL at Postgres to scale. Same code, same behavior (CI proves parity).
🔌 MCP-native	purplesparrow mcp exposes the whole backend as tools for Cursor, Claude, and friends.

Quick start

# one static binary, embedded SQLite — no external services
CGO_ENABLED=0 go build -o purplesparrow ./cmd/purplesparrow
PS_ADMIN_API_KEY=ps_sk_dev ./purplesparrow            # → 127.0.0.1:8787

ADMIN="Authorization: Bearer ps_sk_dev"

# create a table (id + created_at are automatic)
curl -s -H "$ADMIN" -X POST localhost:8787/v1/tables \
  -d '{"name":"todos","columns":[{"name":"title","type":"text"},{"name":"owner_id","type":"text"}]}'

# access is deny-by-default — grant a policy, then use records
curl -s -H "$ADMIN" -X POST localhost:8787/v1/policies \
  -d '{"table":"todos","action":"select","roles":["anon"],"using":"true"}'
curl -s -H "$ADMIN" -X POST localhost:8787/v1/tables/todos/records -d '{"title":"ship","owner_id":"u1"}'
curl -s localhost:8787/v1/tables/todos/records

# introspect · read docs · lint config
curl -s -H "$ADMIN" localhost:8787/meta
curl -s localhost:8787/docs
curl -s -H "$ADMIN" localhost:8787/advisor

Connect an agent: purplesparrow mcp-config prints a client config snippet; purplesparrow mcp runs the MCP stdio server.

What's inside

Agents (MCP · CLI · REST)
        │
   HTTP gateway  — request-id · authn · recovery · access-log · security-headers
        │
  Data+Records · Auth · Storage · Functions · Realtime · Agent layer · Dashboard
        │
  ┌───────────────── Policy engine (deny-by-default, USING + WITH CHECK) ─────────────────┐
  │                   the authorization boundary — one place to get right                  │
  └───────────────────────────────────────────────────────────────────────────────────────┘
        │
   DataEngine · BlobStore · FuncRunner · EventBus ports
        │
   SQLite + local FS (solo)      |      Postgres + S3 (scale)

• Data + policy — tables, records CRUD, PostgREST-style filters; every read row-filtered, every write checked.
• Auth — email/password, RS256 JWTs via JWKS, single-use refresh rotation, hashed API keys.
• Storage — buckets + objects, ownership-scoped access, public buckets, presigned URLs; local FS or S3.
• Functions — edge functions as sandboxed WASM (WASI/wazero): no fs/net/subprocess, explicit secrets, timeout + memory caps.
• Realtime — row-change events over SSE, filtered per subscriber by the policy engine.
• Agent layer — docs-over-API, per-subject memory, an advisor for risky config.
• Dashboard — a dependency-free admin console embedded in the binary, served at /.
• MCP + CLI — the whole surface as agent tools; serve / mcp / mcp-config / version.
• OpenAPI contract — the full REST surface is described in OpenAPI 3.1, served at GET /openapi.yaml and kept in lock-step with the code by a route-parity test.

Status — honest about limits

Beta. The full feature surface is built and tested end-to-end — review it before trusting it with regulated data.

• ✅ Built: M0 foundations · M1 data + policy spine · M2 auth · M3 agent layer · M4 MCP/CLI · M5 Postgres · M6 storage · M7 functions · M8 realtime · M9 dashboard · M10 hardening.
• 🧪 Quality gates: go test -race, go vet, staticcheck, govulncheck — all green. Postgres parity proven in CI.
• 🔬 Reviewed: spec-reviewed per milestone, plus repeated back-to-back adversarial review rounds.
• 🔒 Hardened: deny-by-default everywhere, per-IP rate limiting, CSP + security headers, non-root distroless image, three-tier deploy guide.
• ⚠️ Honest caveats: the policy engine warrants an independent security audit before regulated data; realtime SSE is per-node (a shared-bus adapter for cross-node fan-out is the next step); the WASM memory cap is process-wide, not per-function; S3 and Postgres are CI-verified, not yet battle-tested under production load.

Development

make build     # single static binary
make test      # go test -race ./...
make check     # fmt + vet + staticcheck + govulncheck + test (matches CI)

Contributing & security

Spec-driven, deny-by-default, tests required — see CONTRIBUTING.md. Report vulnerabilities privately via SECURITY.md, not public issues.

License

Apache-2.0. Built in the open. Not affiliated with any other backend platform.