feat(hooks): Add Hooks Server PreToolUse schema by tgasser-nv · Pull Request #2472 · NVIDIA-NeMo/Guardrails

tgasser-nv · 2026-10-19T17:26:48Z

Description

Adds Pydantic classes for Claude Code, Codex, and NeMo Relay client for use in later PRs creating the hooks-server. The hooks-server is an independent server implementation which support agentic-hooks.

This is part of a PR stack:

feat(hooks): Add Hooks Server PreToolUse schema #2472 : Pydantic Classes with mapping to docs
feat(hooks): Add Hooks Server #2473 : Hooks-server FastAPI implementation
TODO: Move allow-list out of main model and into rails.config, add block-list
TODO: Hooks-server OTEL telemetry
TODO: Hooks-server docs
TODO: Hooks-server integration-tests with vcrpy

Related Issue(s)

NGR-1001

Verification

Pre-commit

$ uv run pre-commit run --all-files
check yaml...............................................................Passed
fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed
ruff (legacy alias)......................................................Passed
ruff format..............................................................Passed
Insert license in comments...............................................Passed
zizmor...................................................................Passed
ty.......................................................................Passed

Unit-test

$ make test
env -u OPENAI_API_KEY -u NVIDIA_API_KEY -u LIVE_TEST -u LIVE_TEST_MODE -u TEST_LIVE_MODE uv run pytest -n auto --dist worksteal  
============================= test session starts ==============================
platform darwin -- Python 3.13.2, pytest-9.1.1, pluggy-1.6.0
rootdir: /Users/tgasser/projects/nemo_guardrails_worktree/feat/hooks-api-models
configfile: pytest.ini (WARNING: ignoring pytest config in pyproject.toml!)
testpaths: tests, benchmark/tests
plugins: langsmith-0.9.4, inline-snapshot-0.33.0, recording-0.13.4, cov-7.1.0, anyio-4.14.1, xdist-3.8.0, asyncio-1.4.0, httpx-0.36.2, profiling-1.8.1
asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
created: 10/10 workers
10 workers [9483 items]

====================== 9263 passed, 220 skipped in 42.50s ======================

AI Assistance

No AI tools were used.
AI tools were used; a human reviewed and can explain every change (tool: Claude Code).

Checklist

I've read the CONTRIBUTING guidelines.
This PR links to a triaged issue assigned to me.
My PR title follows the project commit convention.
I've updated the documentation if applicable.
I've added tests if applicable.
I've noted any verification beyond CI and any checks I couldn't run.
I did not update generated changelog files manually.
I addressed all CodeRabbit, Greptile, and other review comments, or replied with why no change is needed.
@mentions of the person or team responsible for reviewing proposed changes.

Summary by CodeRabbit

New Features
- Added support for processing tool-call hooks from Claude Code, Codex, and NeMo Relay, including request validation and responses that allow, deny, or report errors.
- Tool-call decisions now include relevant block reasons and support agent-specific response formats.

greptile-apps · 2026-10-19T18:45:52Z

Confidence Score: 5/5

[Medium impact] This PR appears safe to merge, with the dependent server update in PR #2473.

Summary

Adds request models and adapters for Claude Code, Codex, and NeMo Relay hooks.

Agent hooks now turn tool requests into agent-specific replies.
Tool checks now map engine results to allow, deny, or error outcomes.

No new actionable issues were found. The earlier server compatibility issue is fixed in dependent PR #2473, not in this PR; that assessment depends on #2473.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Agent hook body] --> B[Agent adapter]
  B --> C[ToolInvocation]
  C --> D[check_messages]
  D --> E[Tool-call checks]
  E --> F[outcome_from_result]
  F --> G{HookOutcome}
  G -->|allow or deny| H[Agent response]
  G -->|error| I[Error status]

_{Reviews (6) · Last reviewed commit: "Refactor into adapters which convert to ..." · Reviewed by Greptile}

coderabbitai · 2026-10-19T18:50:53Z

📝 Walkthrough

The new nemoguardrails.server.hooks package defines request models and parsing for Claude Code, Codex, and NeMo Relay. It also converts hook requests to tool-call messages, maps RailsResult values to outcomes, and renders responses for the supported agents.

Changes: Hook request and outcome mapping

Layer / File(s)	Summary
Hook request schemas and parsing `nemoguardrails/server/hooks/schemas.py`, `tests/server/test_hooks_models.py`	Adds agent-specific request models and event dispatch. Tests cover request validation, unsupported events, and Codex schema compatibility.
Hook messages and outcome rendering `nemoguardrails/server/hooks/mapping.py`, `nemoguardrails/server/hooks/__init__.py`, `tests/server/test_hooks_models.py`	Adds tool-call message conversion, outcome construction from `RailsResult`, and agent-specific response rendering. Tests cover conversion, outcome rules, and rendered responses.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Merge Risk: 🔵 Low · up to e36af

A tool call can be denied when its guardrail actually failed, hiding the failure from the hook client. Correct the mapping before merge or accept this bounded risk.

Pre-merge checks: 6

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage		Docstring coverage is 93.10% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 58 functions across 4 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Test Results For Major Changes		The PR adds a substantial new hook-model feature: 1,146 lines across three new implementation modules and a 775-line test module. The description documents testing information, including `make test` r…
Title check		The title clearly identifies the main change: adding Hooks Server PreToolUse schemas. It is concise and related to the pull request objectives.

Full details: Test Results For Major Changes

Explanation

The PR adds a substantial new hook-model feature: 1,146 lines across three new implementation modules and a 775-line test module. The description documents testing information, including make test results of 9,263 passed and 220 skipped, plus successful pre-commit checks. The change does not concern numerics, convergence, or performance.

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Inline comments:
Review comments at @nemoguardrails/server/hooks/mapping.py:
- Around line 103-115: Update _blocked_outcome to preserve its existing
all-RAIL_FAILED error branch unchanged, then handle mixed failures as errors
only when result.content is INTERNAL_ERROR_MESSAGE, at least one violation is
RAIL_FAILED, and every violation is a recognized failure type (RAIL_FAILED,
MALFORMED_ARGUMENTS, MALFORMED_TOOL_CALL, or LEGACY_FUNCTION_CALL); keep other
results on the existing deny path.

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📥 Commits

Reviewing files that changed from the base of the PR and between de1bd2d and e36afb3.

📒 Files selected for processing: 4

nemoguardrails/server/hooks/__init__.py
nemoguardrails/server/hooks/mapping.py
nemoguardrails/server/hooks/schemas.py
tests/server/test_hooks_models.py

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Pouyanpi

this looks like a good starting point 👍🏻

my review is not finished yet; I’ve left initial comments on schema compatibility and failure classification, plus adapter-organization suggestion in mapping.py. more feedback may follow.

…int validation

…gnostic code

tanushriya910 · 2026-10-21T06:43:25Z

+    violations = result.tool_violations or []
+    # A block that reports no violations still blocks, so it is a deny rather than an error.
+    if violations and all(violation.violation_type in _CHECK_FAILURES for violation in violations):
+        return _check_failed_outcome(violations)


wanted to check the rationale behind returning an error in case of all-failures case since the agents will block on explicit deny in a 2xx response. Shouldn't we lean towards blocking this as well for safety reasons. There is definitely an availability tradeoff though in case all the rails are failing cause of downstream dependency being down.

I see the safety concern here. I wonder if we could keep the evaluation error distinct and let the hook decide how to handle it, for example retrying a transient failure while keeping the tool call pending ... that would avoid letting the call proceed unchecked without making every evaluation failure an immediate deny.

The _check_failed_outcome() will return a 500 error, the behaviour depends on the harness.

Claude code has an onFailure setting which controls what to do in this case. If it's set a failure is converted to a block. I'd rather keep this policy in the harness where it already exists.

Codex uses curl commands, adding a -f to the options turns a 500 HTTP code into exit 2 which will block.

Relay (for which we own the client) Uses Err(...) to indicate an error.

I'd rather return a true representation of what happened and let the harness decide based on its policy. If it ends up being a problem we can add a config field (block_on_error or similar) to allow users to control this at the Guardrails-level.

cc @Pouyanpi , @tanushriya910

Pouyanpi

thanks for the updates! lgtm 👍🏻

github-actions Bot added status: needs triage New issues that have not yet been reviewed or categorized. size: L labels Oct 19, 2026

tgasser-nv self-assigned this Oct 19, 2026

tgasser-nv marked this pull request as ready for review October 19, 2026 18:37

tgasser-nv added status: triaged Triaged by a maintainer; eligible for automated review (CodeRabbit/Greptile). and removed status: needs triage New issues that have not yet been reviewed or categorized. labels Oct 19, 2026

greptile-apps Bot reviewed Oct 19, 2026

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Comment thread nemoguardrails/server/hooks/schemas.py Outdated

coderabbitai Bot reviewed Oct 19, 2026

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Comment thread nemoguardrails/server/hooks/checking.py

tgasser-nv requested review from Pouyanpi and tanushriya910 October 19, 2026 19:43

tgasser-nv changed the title ~~feat(hooks): Add PreToolUse hook models~~ feat(hooks): Add PreToolUse hook schema Oct 19, 2026

tgasser-nv changed the title ~~feat(hooks): Add PreToolUse hook schema~~ feat(hooks): Add Hooks Server PreToolUse schema Oct 19, 2026

tgasser-nv mentioned this pull request Oct 19, 2026

feat(hooks): Add Hooks Server #2473

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tgasser-nv added this pull request to stack #2474 October 19, 2026 21:53

Pouyanpi reviewed Oct 20, 2026

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Comment thread nemoguardrails/server/hooks/schemas.py Outdated

Comment thread nemoguardrails/server/hooks/schemas.py Outdated

Comment thread nemoguardrails/server/hooks/checking.py

Comment thread nemoguardrails/server/hooks/checking.py

greptile-apps Bot reviewed Oct 20, 2026

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Comment thread nemoguardrails/server/hooks/__init__.py

tgasser-nv added 6 commits October 20, 2026 17:28

Initial checkin of PreToolUse hook Pydantic models

b6a4a69

Exclude model and turn_id fields from model dumps

9bb1691

Test fail-closed for any set of check results containing a failure

9954405

Remove unused fields from Codex and Claude PreToolUse and cross-endpo…

6fcf2e3

…int validation

Tighten check failures by checking all relevant ToolViolations

e964293

Refactor into adapters which convert to a common schema and harness-a…

28f795e

…gnostic code

tgasser-nv force-pushed the feat/hooks-api-models branch from 1fa645a to 28f795e Compare October 20, 2026 22:30

tgasser-nv added a commit that referenced this pull request Oct 20, 2026

Use harness-adapters from #2472

59ed6b1

tanushriya910 reviewed Oct 21, 2026

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Pouyanpi approved these changes Oct 21, 2026

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feat(hooks): Add Hooks Server PreToolUse schema - #2472

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