Custody

Custody sits between an AI agent and the tools it uses on oncology data, so the agent can work under controls a privacy or compliance officer can actually review: data-aware policy, approval gates for anything sensitive, a tamper-evident audit log, and isolated execution for every command.

Agent (Claude Code / Codex / OpenHands / Goose / any MCP client)
   |  MCP (stdio or streamable HTTP)
   v
Custody Gateway
   1. Identify principal + session
   2. Classify request (tool, datasets, data class, egress, model target)
   3. Policy engine  -> allow | deny | require_approval
   4. Approval broker -> wait for human decision (timeout = deny)
   5. Executor       -> sandboxed container
   6. Output guard   -> redact/summarize results by data class
   7. Audit log      -> hash-chained entry at every step
   |
   v
Custody's own tools: catalog.list, sql.query, shell.run, files.write,
files.export, approvals.status, fhir.search

Status: v0.1.0 tagged and public (285 tests, 96% coverage on src/custody, ruff and mypy --strict clean); main carries several items since merged in from ROADMAP.md (signed policy bundles, an OPA policy backend, a Kubernetes deployment, a FHIR connector, an S3 Object Lock audit sink, an egress allowlist proxy, OIDC-verified approver identity) -- see CHANGELOG.md's [Unreleased] section for exactly what, and for what shipped in v0.1.0 itself. One scope note: the architecture above describes a gateway that can also proxy a downstream MCP server's tools, that proxying is not implemented, every tool call this release handles goes through one of the built-ins listed above (see custody/mcp_server.py's module docstring).

Quickstart (under 5 minutes to the demo, Docker required)

custody-mcp is on PyPI (pip install custody-mcp) for the CLI and the gateway itself. The demo specifically needs a clone, though: it builds the sandbox's DuckDB image from docker/sandbox.Dockerfile, which only a clone carries.

git clone https://github.com/unmirihealth/custody
cd custody
uv sync --extra dev
docker build -f docker/sandbox.Dockerfile -t custody-sandbox:duckdb .
uv run custody demo

custody demo generates a synthetic oncology dataset with a fixed seed, writes a sample policy/catalog/principals to disk, and walks through: an allowed catalog listing, a de-identified cohort query (not small-cell suppressed, that only applies at limited_data_set and above), the same cohort breakdown re-run on identified data (held for approval, then approved, this time suppressed), a two-person export denied by one of the two required approvers, a blocked network call from the sandbox, and custody audit verify catching a deliberately tampered log entry. See docs/demo.md for a narrated walkthrough of the output.

Once initialized (custody init in an empty directory, or after custody demo), run custody serve --principal <your-agent-id> to start the real MCP gateway (stdio), or custody ui for the local approvals web UI.

Related MCP server: sentinel-mcp

Using it with Claude Code

Two integration modes:

• MCP gateway (primary). Custody runs as an MCP server (custody serve) exposing its built-in tools. See examples/claude-code-mcp-config.json for the config snippet.

• PreToolUse hook adapter (secondary). Routes Claude Code's own native tool calls (Bash, Write, Edit, WebFetch) through the same policy engine and audit log, as claude_code.bash / claude_code.write / claude_code.edit / claude_code.web_fetch in your policy. A require_approval decision here doesn't block the hook (a PreToolUse hook has roughly 30 seconds, Custody's default approval timeout is 15 minutes); it records the pending approval and returns Claude Code's own "ask" decision instead.

See docs/integrations/claude-code.md for both, with exact config.

What Custody is not

• Not a HIPAA certification. Installing Custody does not make anyone compliant. The accurate phrase is that Custody provides controls that can support HIPAA-aligned programs.

• Not an audit or a SOC 2 report. custody evidence export produces a mechanical summary of the audit log and policy, mapped to SOC 2 Common Criteria language, for a reviewer's convenience. It is not an attestation and does not substitute for an independent auditor. See docs/evidence-pack.md.

• Not a replacement for a business associate agreement, a risk assessment, or your institution's review process.

• Tamper-evident, not tamper-proof. The audit log detects changes; it does not make them physically impossible. For long-term retention, ship checkpoints to write-once storage (see docs/audit-log.md).

• Not a perfect sandbox. Docker isolation is one layer in a defense-in-depth design, not the whole design. See docs/threat-model.md for exactly what v0.1 defends against and what it does not.

• Not a full SSO login flow. principals.yaml is still the one source of truth for which roles a principal holds. custody approvals approve/deny --as-token can verify an approver's identity against a real OIDC provider's signed token instead of trusting a bare --as string (see docs/sso-oidc.md), but there is no browser login flow, no session management, and the approvals web UI is unaffected (still its own startup-token gate).

• Not sandboxed with gVisor or Firecracker. Both require a Linux host with KVM; neither is buildable or verifiable on a macOS development machine, so neither is implemented here, see docs/threat-model.md T2 and ROADMAP.md.

Components

Synthetic data only

Every example, fixture, and test in this repository uses generated oncology records. No real patient data belongs anywhere near this project, in an issue, a PR, or a commit. See CONTRIBUTING.md.

License

Apache 2.0. See LICENSE and NOTICE.