Verb Authority

Prevent untrusted data from authoring protected tool-call arguments.

Consider a tool exposed to an AI agent:

send_email(to: str, body: str)

The model may write body. The recipient to must come from trusted application code, such as an authenticated session or an application-owned directory. If a webpage, retrieved document, model response, or prior tool result supplies a different recipient, the call must stop before send_email runs.

Tool schemas validate shape. They do not prove who may supply each value.

Verb Authority scans exported tool schemas, produces a reviewable per-argument authority map, and provides a small local runtime gate. It does not invoke tools while scanning and does not upload schemas.

Install beta.15

Publication status: the commands below target 0.10.0b15. Check PyPI for package-index availability and the beta.15 GitHub release for published artifacts and their hashes. A source version or branch does not itself establish publication. If that release is not available yet, evaluate this checkout with python -I -m pip install . instead.

Install the dependency-free core from PyPI once available:

python -m pip install "verb-authority==0.10.0b15"

Or install the same release tag directly from GitHub once published:

python -I -m pip install "verb-authority @ git+https://github.com/yairsabag/verb-authority.git@v0.10.0-beta.15"

The dependency-free core supports Python 3.10 through 3.14. See installation and package-integrity details for isolated-environment guidance, local checkout installation, wheel hashes, and the optional Pydantic AI extra.

Run the offline quickstart

python -I -m verb_authority quickstart

The command uses no model, network, or email service. It scans one exported schema and routes three local calls through the runtime boundary.

Expected result excerpts:

1) SCAN THE EXPORTED TOOL SCHEMA
   send_email.to    -> trusted_fixed
   send_email.body  -> outbound_payload

3) GATE RUNS IMMEDIATELY BEFORE EXECUTION
   BLOCKED - param 'to' is a locked sink; data may not author it
   local tool invocations=0

4) THE SCHEMA LIMIT IS ALSO ENFORCED AT RUNTIME
   body length=2001; registered maxLength=2000
   BLOCKED - param 'body' failed its type/bounds check
   local tool invocations=0

ALLOWED - within authority
local tool invocations=1

The demo implementation only increments an in-memory counter. It never sends email. In the allowed control, the recipient value is supplied independently by application code; the demo does not implement a human approval workflow.

Why this boundary matters

A provider typically gives every model-visible argument the same JSON Schema surface:

{
  "name": "send_email",
  "inputSchema": {
    "type": "object",
    "properties": {
      "to": {"type": "string"},
      "body": {"type": "string", "maxLength": 2000}
    },
    "required": ["to", "body"]
  }
}

Both fields are strings, but they carry different authority:

Verb Authority makes that distinction explicit and checks it immediately before execution.

Preferred remediation: keep protected arguments out of the model schema

When the application already owns the recipient, prefer exposing a smaller tool to the model:

# Canonical tool registered by the application
send_email(to: str, body: str)

# Conceptual model-visible interface
send_reply(body: str)

The application restores to from state established independently of untrusted content; the canonical registration and implementation stay intact. send_reply is a conceptual interface, not a shipped wrapper or alias API.

If the schema cannot change, materialize the application-owned value in the canonical call and pass the same exact value in trusted_args. It verifies a match; it never inserts or overwrites input. See the complete runtime contract and the optional projection design.

Scan a real MCP schema

Export the tools/list JSON your client already receives. Then run:

python -I -m verb_authority scan tools.json --output authority-report.md

The scanner accepts:

• MCP tools/list responses;
• OpenAI function-tool definitions; and
• Anthropic tool definitions.

It keeps the schema local, never starts the MCP server, and never invokes a tool. The report separates argument authority, review obligations, effective risk, advisory name signals, and author-supplied control evidence.

From a repository checkout, try the frozen 23-tool Playwright MCP fixture:

python -I -m verb_authority scan fixtures/external/sankalp-gilda/playwright-browser-tabs/frozen/tools-list.json --format json --output authority-report.json

Use --redact-names before sharing a report, then still review the output. Stable hashes and author-written evidence can remain correlatable or dictionary-guessable. See the full scanner and report privacy contract.

Have one real or redacted schema?

Issue #7: Real-schema clinic is the main feedback path. Report one missed lock, unnecessary lock, incorrect risk tier, or wrong confirmation decision. A small redacted fixture is enough; do not post secrets or private deployment data.

Put the gate before execution

GuardedToolRunner freezes the registered tool and policy state, calls the gate immediately before the registered synchronous function, binds any confirmation to the exact arguments and callable, and records successful plain-JSON results in one session ledger.

from verb_authority import GuardedToolRunner, Param, Registry, Risk, Tool

def send_email(to: str, body: str) -> dict:
    # Trusted application implementation.
    return {"sent": True, "to": to}

registry = Registry()
registry.add(
    Tool(
        "send_email",
        [
            Param("to", "email", sink=True),
            Param("body", "string", max_len=2000, sink=False),
        ],
        fn=send_email,
        risk=Risk.WRITE,
    )
)

runner = GuardedToolRunner(registry)

# Read independently from authenticated application state—not model content.
session_recipient = "alice@company.com"

tool_call = {
    "name": "send_email",
    "input": {
        "to": session_recipient,
        "body": "Meeting summary",
    },
}

execution = runner.run(
    tool_call,
    trusted_args={"to": session_recipient},
)
assert execution.executed, execution.decision.reason

Normalize provider-specific calls to the small {"name": ..., "input": ...} shape before dispatch. Every execution route must pass through the runner. Risk tiers that require confirmation also need a trusted synchronous confirm callback. The surrounding application remains responsible for authentication, business authorization, request freshness, rate limits, and external-state synchronization.

Read the complete runtime gate contract before a real integration. It covers exact argument snapshots, confirmation binding, callable identity, resource budgets, ledger saturation, error/no-retry behavior, trusted catalog resolution, selector branches, and the pinned Pydantic AI adapter.

Pydantic AI

The Python package includes an optional, narrowly pinned Pydantic AI adapter. It keeps protected values out of the model-visible function or resolves model-visible keys through an application-owned catalog before entering GuardedToolRunner.

python -m pip install "verb-authority[pydantic]==0.10.0b15"

The adapter supports only the audited local, synchronous paths documented for the pinned dependency versions. Unsupported remote, runtime-added, streaming, async, realtime, and native execution paths fail closed. See Pydantic AI 2.35 runtime adapter.

No JavaScript/TypeScript runtime adapter is included in this Python release. JavaScript applications may export JSON schemas for an offline scan, but runtime enforcement must sit in a trusted server-side boundary rather than a browser bundle. See the JavaScript and TypeScript evaluation path.

Catch authority drift in CI

Compare a protected baseline schema with the candidate schema:

python -I -m verb_authority diff tools-main.json tools-pr.json --fail-on-increase --fail-on-review

Or use the composite GitHub Action:

- uses: actions/checkout@v7
- uses: actions/setup-python@v7
  with:
    python-version: "3.12"
- uses: yairsabag/verb-authority@v0.10.0-beta.15
  with:
    before: tools-main.json
    after: tools-pr.json
    fail_on_increase: "true"
    fail_on_review: "true"

The baseline must come from a protected revision or trusted artifact, and the candidate export must correspond to the implementation that will run. A diff does not authenticate either input or verify implementation behavior. See the full Authority Diff contract.

Promise boundary

• The enforced claim is per-argument provenance before execution.
• A schema scan infers a reviewable policy; it does not prove what an implementation does.
• The gate does not classify prompts or prevent every prompt-injection effect.
• It is not business authorization and does not validate arbitrary cross-argument, transaction, tenant, sequence, or purpose rules.
• Untrusted content can still influence whether a tool is called or which member of an already trusted catalog is selected.
• The optional ledger recognizes exact, contained, and selected lexical forms; it does not track arbitrary semantic rewrites.
• The gate provides argument-integrity control, not confidentiality, secret tracking, or model-output filtering.
• Any execution route that bypasses the gate is outside the guarantee.
• No real incident is claimed covered without an exact replay and regression; see the incident coverage matrix.

Read Limits and boundaries before using a report or allowed decision as security evidence.

How policy inference works

The scanner and core use conservative, reviewable defaults:

• destination-like arguments such as recipients, URLs, accounts, paths, and commands default to trusted_fixed;
• free-text payloads such as bodies may be outbound_payload;
• ambiguous arguments on consequential tools remain locked and require review;
• type membership, an enum, or a numeric type does not by itself grant model authorship;
• raw schema extensions cannot unlock an argument;
• tool names are mutable advisory signals, not proof of runtime risk; and
• undeclared or conflicting tool risk stays unknown and keeps confirmation enabled.

Trusted registration code can resolve an overloaded argument with Param(..., sink=True|False). A reviewed control sidecar can add implementation evidence to a scan, but the scanner labels that evidence as author-supplied rather than verified.

For exact selector branches, one trusted map can bind every value of one scalar enum selector to risk and active arguments. That map controls applicability and confirmation. It does not authorize the action instance or prove user intent.

See Security model for the complete model.

Documentation

• Security model
• Runtime gate and Pydantic AI adapter
• JavaScript and TypeScript teams
• Schema scanner, control evidence, privacy, and Authority Diff
• Limits and boundaries
• Case studies and executable evidence
• Research/product landscape, citations, and incident coverage
• Fixture contribution layout
• Security reporting
• Changelog

Evidence and project status

The test suite covers inference, declared capabilities, tool risk, selector branches, dispatch, the guarded runner, confirmation binding, ledger containment, schema import, report redaction, Authority Diff, the Pydantic AI adapter, packaging, and frozen external regressions.

Public case material is preserved separately from CI reductions:

• external risk-tier case study;
• frozen Playwright browser_tabs contribution;
• Tool Authority Atlas, a small source-pinned corpus rather than a ranking of MCP servers; and
• executable demos.

v0.9.0 is the latest stable release. Beta.14 was the first PyPI distribution. Beta.15 adds report-v6 remediation guidance, a first-look review summary, nested-schema review coverage, and corrected integration examples. It retains the runtime API, offline quickstart, and frozen external regression evidence. Report-v5 consumers should review the compatibility notes before upgrading. The beta.7, beta.8, and beta.9 identifiers were withheld and will not be reused. This remains early, research-grade work and is not described as production-ready.

Contributing

Start with one public or redacted schema fixture and one expected authority boundary. CONTRIBUTING.md explains the fixture format, provenance expectations, tests, and focused contribution process.

For sensitive vulnerabilities, do not open a public issue; follow SECURITY.md.

For real-schema product feedback, use Issue #7.

Licensed under Apache-2.0.