pywrit

Find the dangerous writes in your Python agent's code, then gate it. pywrit is the Python client and writ CLI for Writ: an allow/deny gate that sits in front of your agent's consequential writes (database, HTTP, files, email, queues, AWS) and records a hash-chained receipt for every decision.

writ scan is local, deterministic, and free: it parses your code with Python's ast module, makes no network calls, and needs no API key.

Install

pip install pywrit

Requires Python 3.9+. Installs the writ command and the pywrit Python client.

60-second quickstart: scan → apply → gate

1. Scan. See which functions write, and how many of them are gated.

writ scan .

writ scan: /path/to/support-agent
  files scanned: 4  skipped: 0
  write sites: 4 in 3 function(s)
  gated: 0/4 (0%)
  verbs discovered: 3
    crm.update
    payments.refund
    tickets.close

It also prints a risk report (0-100, weighted by risk tier), writes the discovered verbs to writ-policy.json, and shows the instrumentation it would add as a unified diff. Nothing in your code changes yet. writ scan . --score prints just the risk report.

2. Apply. Insert a gate at the top of each writing function.

writ scan . --apply        # shows the diff, then asks before writing
writ scan . --apply --yes  # no prompt (e.g. in CI)

Each gated function now asks Writ before it writes, and fails closed:

def issue_refund(charge_id, amount_cents):
    if _writ_check("payments.refund") != "ALLOW":
        raise PermissionError("writ denied payments.refund")
    ...

Re-run writ scan . and you'll see gated: 4/4 (100%).

3. Gate. Get a free API key, load the discovered policy, and run your agent.

writ key --email you@example.com                  # free API key + tenant
export WRIT_API_KEY=writ_...                      # read by the inserted gate
export WRIT_SPONSOR=acme WRIT_AGENT=support-agent # optional: who is acting
writ scan . --push-policy --key "$WRIT_API_KEY"   # upload the discovered verb policy

Every gated write now gets ALLOW, DENY, or STEP_UP (a human sponsor must approve), and every decision is written to your tenant's tamper-evident audit log:

writ receipts --key "$WRIT_API_KEY"       # latest receipts
writ verify-chain --key "$WRIT_API_KEY"   # verify the receipt hash chain
writ stream --key "$WRIT_API_KEY"         # tail decisions live
writ report --key "$WRIT_API_KEY"         # Agent Action Report

What writ scan detects

Python (.py) files, parsed with the stdlib ast (no extra dependencies):

• Each write is mapped to a verb such as payments.refund or crm.update, inferred from the file path and function name.
• A function that already calls writ_check(...) / _writ_check(...) counts as gated.
• Skipped: tests, hidden directories, virtualenvs, node_modules, dist, build. Use --exclude SUBSTR (repeatable) to skip more.
• Not covered (review by hand): writes behind dynamically built SQL, third-party SDK calls such as stripe.Refund.create(...), deferred task queues, or shared clients several layers down. The risk report lists these gaps every time.

TypeScript / JavaScript (scan-only)

writ scan also finds write sites in TypeScript and JavaScript. It needs the optional extra (tree-sitter based):

pip install 'pywrit[polyglot]'
writ scan .

Without the extra, the scanner prints a one-line hint and keeps going — Python scanning never needs it.

TS/JS is scan-only: findings are listed with verbs for your policy file, but writ scan --apply never rewrites TS/JS files — gate those by hand. Covered patterns: fetch/axios writes, fs writes, SQL through knex-style clients, Prisma writes, and JS SDK calls such as stripe.refunds.create(...). (Still not covered: the Python SDK equivalents like stripe.Refund.create(...) — see "Not covered" above.)

Python client

from pywrit import WritClient

client = WritClient(api_key="writ_...")

result = client.check(
    sponsor_id="acme",
    agent_id="agent-7",
    verb="db.write",
    target="prod.customers",
    purpose="backfill region field",
)

if result.decision == "ALLOW":
    # result.auth_token is a short-lived token bound to this exact write
    perform_write(...)
elif result.decision == "STEP_UP":
    # a human sponsor must approve first: client.grant(...), then re-check
    ...
else:
    # DENY
    ...

No API key yet? Try the keyless sandbox:

client = WritClient()
client.sandbox({
    "sponsorId": "acme",
    "agentId": "agent-7",
    "verb": "demo_write",       # sandbox only allows demo_write ...
    "target": "demo-customers", # ... on targets starting with demo-
    "purpose": "trying the gate",
})

What's covered:

• check(...): the gate. ALLOW / DENY / STEP_UP, plus a receipt every time
• verify_token(...): validate an ALLOW auth token (catches purpose drift)
• grant(...): human-sponsor approval for the STEP_UP path
• get_policy() / set_policy(...): manage the tenant policy
• revoke(...) / reinstate(...) / revoked(): the kill switch
• receipts() / receipt(id) / verify_chain() / stream_receipts(): the audit log
• sandbox(...): keyless trial, no API key required

CLI reference

writ check --key writ_... --sponsor acme --agent agent-7 \
  --verb db.write --target prod.customers --purpose "backfill region field"
writ policy --key writ_... --set payments.refund require_grant
writ revoke --sponsor acme --agent agent-7 --reason "runaway loop"   # kill switch (sponsor token)
writ grant --sponsor acme --agent agent-7 --verb payments.refund \
  --target ch_123 --purpose "approved refund"                        # STEP_UP approval (sponsor token)

Sponsor-token commands (revoke, reinstate, revoked, grant) read --sponsor-token or WRIT_SPONSOR_TOKEN. Run writ --help for the full command list.

Docs

Full docs: docs.withwrit.com · Quickstart: docs.withwrit.com/quickstart · Site: withwrit.com

License

MIT