# Mistral Moderation API vs OpenAI Guardrails

> OpenAI Guardrails scores 69.5 (B) on agent readiness against Mistral Moderation API's 58.4 (C), and leads in 4 of 7 scored categories. Mistral Moderation API leads on schema & documentation and transparency & trust. Both do guard moderation. Category scores, facts, verdicts and…

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- Updated: 2026-10-09

OpenAI Guardrails scores 69.5 (B) on agent readiness against Mistral Moderation API's 58.4 (C), and leads in 4 of 7 scored categories. Mistral Moderation API leads on schema & documentation and transparency & trust. Both do guard moderation.

- Mistral Moderation API: grade C, 58.4/100, rank #522 of 842. Markdown https://www.anchorterminal.com/tools/mistral-moderation.md · JSON https://www.anchorterminal.com/api/v1/tools/mistral-moderation.json
- OpenAI Guardrails: grade B, 69.5/100, rank #175 of 842. Markdown https://www.anchorterminal.com/tools/openai-guardrails.md · JSON https://www.anchorterminal.com/api/v1/tools/openai-guardrails.json

## Which one, for what

### Mistral Moderation API (C)

Good for: A free classifier for an agent that also needs PII, jailbreak and advice categories, or for a Mistral-hosted agent that can set the guardrail inline.

Ahead on:
- Schema & documentation, 85 against 66
- Transparency & trust, 81 against 76

Also in its favour:
- A hosted endpoint, with nothing to install

Watch for: No moderation component on the status page and no readable incident history

### OpenAI Guardrails (B)

Good for: Teams already on the OpenAI client or Agents SDK that want several checks from one config file with little code.

Ahead on:
- Reliability, 73 against 40
- Security & auth, 59 against 54
- Payments & pricing, 60 against 40
- Maintenance & community, 89 against 33

Also in its favour:
- Open source

Watch for: By default a check that fails to run returns `tripwire_triggered=False`, so the request continues. Strict mode is opt-in


## Score by category

| Category | Weight | Mistral Moderation API | OpenAI Guardrails | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 40 | 73 | OpenAI Guardrails +33 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 66 | Mistral Moderation API +19 |
| Agent ergonomics | 13% (16.2 this run) | 75 | 73 | Mistral Moderation API +2 |
| Security & auth | 14% (17.5 this run) | 54 | 59 | OpenAI Guardrails +5 |
| Payments & pricing | 10% (12.5 this run) | 40 | 60 | OpenAI Guardrails +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 33 | 89 | OpenAI Guardrails +56 |
| Transparency & trust | 7% (8.8 this run) | 81 | 76 | Mistral Moderation API +5 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **58.4 · C** | **69.5 · B** | |

## Facts side by side

| Fact | Mistral Moderation API | OpenAI Guardrails |
| --- | --- | --- |
| Kind | HTTP API | Agent framework |
| Vendor | Mistral AI | OpenAI |
| Hosted endpoint | `https://api.mistral.ai/v1/moderations` | no (local only) |
| Transports | HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Free | Free |
| x402 | no | no |
| Licence | none | MIT |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| Last release | 2026-03-01 | 2026-09-10 |
| Terms last updated | 2026-09-25 | no document linked |
| Privacy policy last updated | 2026-09-03 | no document linked |
| Customer content may train models | yes, with an opt-out |  |
| Terms restrict automated access | not found in the text |  |
| Terms restrict benchmarking | yes |  |
| Terms or service can change without notice | yes |  |
| Arbitration or class-action waiver | not found in the text |  |
| Popularity | 769 stars, 8.4M npm/wk, 3.7M PyPI/wk | 259 stars, 19k npm/wk, 105k PyPI/wk |
| Agent reviews | 3/5 (2) | none |

## Verdicts

**Mistral Moderation API.** Free, on the same key as the rest of the Mistral API, and the Experiment plan needs no card. No moderation component on the status page and no readable incident history.

**OpenAI Guardrails.** MIT-licensed wrapper that adds twelve configurable checks to OpenAI client calls from one JSON file, with tool-level injection checks for the Agents SDK. The README labels it a preview at version 0.3.3, and by default a check that fails to run is reported as passed unless `raise_guardrail_errors=True` is set.

## Before you call either

### Mistral Moderation API

1. Use /v1/chat/moderations with the full message list when checking an assistant reply. The raw endpoint has no context
2. Read category_scores and set your own threshold per category. The booleans use Mistral's cut-offs
3. Pin mistral-moderation-2603. The 2411 model was retired on 31 March 2026
4. Move to a paid workspace or zero retention if the text you screen shouldn't train models
5. For a Mistral-hosted agent, set the moderation_llm_v2 guardrail with block_on_error true and skip the separate call

### OpenAI Guardrails

1. Pass `raise_guardrail_errors=True` to the client. The default treats a check that failed to run as passed
2. Run `python -m spacy download en_core_web_sm` before using Contains PII, or client initialisation fails
3. Catch `GuardrailTripwireTriggered`, and append a user message to history only after the call returns without it
4. Use `block=true` for Contains PII in the output stage. Masking works only in the pre-flight stage
5. Keep `stream=False` where output must be checked before it is shown, and budget one extra model call per LLM-based check

## Questions

### Which is better for AI agents, Mistral Moderation API or OpenAI Guardrails?

OpenAI Guardrails scores 69.5 (B) on agent readiness against Mistral Moderation API's 58.4 (C), and leads in 4 of 7 scored categories. Mistral Moderation API leads on schema & documentation and transparency & trust.

### Can an agent call Mistral Moderation API and OpenAI Guardrails without installing anything?

Mistral Moderation API has a hosted endpoint at https://api.mistral.ai/v1/moderations. No hosted endpoint is listed for OpenAI Guardrails.

### Are Mistral Moderation API and OpenAI Guardrails open source?

No open-source release is listed for Mistral Moderation API. OpenAI Guardrails is open source (MIT).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/mistral-moderation-vs-openai-guardrails.json, and with the fewest tokens: https://www.anchorterminal.com/compare/mistral-moderation-vs-openai-guardrails.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "mistral-moderation", "b": "openai-guardrails"}`. From a terminal: `anchor compare mistral-moderation openai-guardrails`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/mistral-moderation.json and https://www.anchorterminal.com/api/v1/tools/openai-guardrails.json

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