6 Best Arthur Shield Alternatives for AI Security in 2026
Not everyone needs enterprise AI monitoring. Here are the best Arthur Shield alternatives for teams of every size.
Why Teams Look for Arthur Shield Alternatives
Enterprise-only pricing — five-figure annual minimums
Arthur Shield requires custom enterprise contracts with multi-month procurement cycles. There's no self-serve tier, no free plan, and no way to start small. Most teams report $25K+ annually as the starting point, with multi-year commitments expected.
Heavy integration — weeks, not minutes
Arthur AI's platform requires significant engineering effort: custom SDK integration, configuration of their model monitoring pipeline, and often professional services engagement. Teams typically report 2-6 weeks from contract signing to first protected endpoint — compared to minutes for SDK-based tools.
Model monitoring platform with security bolted on
Arthur AI was built as a model observability platform (bias detection, explainability, performance monitoring) that added Shield as a security layer. Security is a feature, not the product. The result: broad but shallow threat coverage — hallucination scoring is solid, but prompt injection and exfiltration detection trail purpose-built tools.
No agent framework support or tool call awareness
Arthur Shield validates individual LLM call inputs and outputs. It has no concept of agent frameworks, tool calls, inter-agent delegation, or multi-step workflows. When an attack arrives through a tool's return value or passes between agents, Arthur Shield can't see it.
No custom security policy engine
Arthur Shield applies its built-in rulesets to traffic. You can't define organization-specific policies like 'block tool calls to the payments API from user-supplied prompts' or 'flag sessions accessing >3 database tables.' Security rules are Arthur's, not yours.
How We Evaluated Alternatives
Accessibility
criticalSelf-serve signup, transparent pricing, and free tiers — not enterprise-only.
Integration speed
criticalTime from signup to first protected agent. Days or weeks is too long.
Agent awareness
highNative support for agent frameworks, tool calls, and multi-step workflows.
Security depth
highCoverage across injection, exfiltration, PII, secrets, and escalation.
The Best Arthur Shield Alternatives
1. RuneOur Pick
Developer-first agent security with free tier, 3-line setup, and native framework support. Purpose-built for detecting agent threats.
Strengths
- Free tier + transparent usage-based pricing
- 3-line setup — no professional services needed
- Native agent framework support (5 frameworks)
- Local-first scanning with sub-10ms overhead
- Purpose-built for agent security threats
Weaknesses
- No hallucination detection (focused on security, not quality)
- Newer platform with smaller enterprise presence
2. Lakera Guard
Enterprise prompt injection API with Gandalf-trained detection, now part of Check Point Software.
Strengths
- Battle-tested injection detection
- Enterprise compliance
- Check Point backing
Weaknesses
- Enterprise-only (similar to Arthur)
- Cloud API latency
- Limited scope
3. Guardrails AI
Open-source LLM output validation with 100+ validators for format, toxicity, and quality checking.
Strengths
- Open source and free
- Large validator library
- Good for output quality
Weaknesses
- Output validation, not security
- No agent support
- No monitoring
4. NeMo Guardrails
NVIDIA's open-source toolkit for conversation flow control using Colang programming language.
Strengths
- Open source
- Programmable flows
- NVIDIA backing
Weaknesses
- Colang learning curve
- High latency
- Not security-focused
5. LLM Guard
Open-source, self-hosted toolkit for LLM input/output sanitization.
Strengths
- Fully self-hosted
- Open source
- PII detection
Weaknesses
- Limited maintenance
- No monitoring
- No agent support
6. Pangea AI Guard
Cloud security suite with AI content scanning, PII redaction, and malware detection.
Strengths
- Broader security suite
- PII redaction
- Malware scanning
Weaknesses
- Bundled pricing
- Limited injection detection
- No agent awareness
Side-by-Side Comparison
| Feature | Rune | Lakera Guard | Guardrails AI | NeMo Guardrails | LLM Guard | Pangea AI Guard |
|---|---|---|---|---|---|---|
| Self-serve signup | Yes (free tier) | No (enterprise) | Yes (open source) | Yes (open source) | Yes (open source) | Limited trial |
| Setup time | Minutes | Days (procurement) | Hours | Days (learn Colang) | Hours | Hours |
| Agent framework support | 5 frameworks | None | None | Colang only | None | None |
| Security focus | Purpose-built | Injection-focused | Output validation | Topic control | Input sanitization | General security |
Considering Switching to Rune?
How Rune solves the Arthur Shield problems
Start free, scale transparently — no procurement
10K events/month free, no credit card, no sales calls. pip install runesec and you're scanning in under 5 minutes. Usage-based pricing at $0.05/1K scans after that. No enterprise contracts, no multi-year commitments, no procurement cycles.
3-line integration — no professional services needed
`shield = Shield(client)` wraps your existing agent client as middleware. Zero changes to agent logic, zero configuration files, zero professional services. Compare to Arthur's multi-week integration involving their SDK, monitoring pipeline setup, and custom configuration.
Native agent framework support for 6 frameworks
Built for LangChain, OpenAI, Anthropic, CrewAI, MCP, and OpenClaw. Scans tool arguments before execution, tool return values for exfiltration, and inter-agent messages for injection — attack surfaces that Arthur Shield's LLM-call-level validation can't see.
Purpose-built for agent security — not monitoring with security added
Every feature in Rune is designed for detecting and blocking agent threats: injection, exfiltration, PII leaking, secret exposure, privilege escalation. No hallucination scoring, no bias detection, no explainability features — just security done deeply.
YAML policy engine for custom rules
Define organization-specific security policies: restrict which tools an agent can call, set rate limits on sensitive operations, require approval for high-risk actions. Policies are version-controlled and auditable. Arthur Shield offers fixed rulesets — Rune gives you the policy engine.
You should switch if...
- You don't want to negotiate an enterprise contract for security tooling
- You need to start protecting agents today, not after a multi-week integration
- You use agent frameworks and need native tool call scanning
- You want transparent, usage-based pricing
- You prefer a focused security tool over a broad monitoring platform
How to switch from Arthur Shield to Rune
- 1Install the Rune SDK: pip install runesec
- 2Initialize Shield on your agent client (3 lines of code)
- 3Map relevant Arthur Shield rules to Rune YAML policies
- 4Verify detection with test attack payloads
- 5Remove Arthur Shield SDK and API dependencies
Our Recommendation by Use Case
Developer teams with self-serve requirements
RuneFree tier, 3-line setup, no procurement. The fastest path from zero to protected agents.
Enterprise with existing Arthur AI relationship
Arthur Shield (stay with it)If you already have an Arthur AI contract and use their model monitoring, the security add-on makes sense.
Open-source only requirement
Guardrails AI + LLM GuardCombine output validation (Guardrails AI) and input scanning (LLM Guard) for a self-hosted stack.
Frequently Asked Questions
Does Rune offer hallucination detection like Arthur Shield?
No — and that's intentional. Rune focuses on security threats: injection, exfiltration, PII, secrets, and escalation. Hallucination detection is a quality/accuracy concern, not a security concern. If you need both, pair Rune (security) with Guardrails AI (output quality) or keep Arthur Shield specifically for hallucination scoring.
Is Rune enterprise-ready even without enterprise pricing?
Yes. Rune handles millions of events per month, with SOC 2 Type I compliance in progress, data residency options on the Growth plan, and local-first scanning that keeps raw data on your infrastructure. The difference from Arthur Shield: you don't need a procurement cycle to get started. Start free, prove value, then scale — all self-serve.
What's the honest case for staying with Arthur Shield?
If you already have an Arthur AI contract for model monitoring (bias, explainability, performance) and want to add security as an incremental feature, Shield makes sense — it's already in your pipeline. Arthur's hallucination detection is also genuinely strong. The case for switching to Rune: you want deeper agent security (tool call scanning, exfiltration detection, custom policies) without the enterprise overhead.
How does the total cost compare for a mid-size team?
A team scanning 500K agent events/month would pay roughly $25/month on Rune ($0.05/1K scans). Arthur Shield's enterprise minimums typically start at $25K+/year. Even at 5M events/month, Rune's pricing is $250/month — an order of magnitude less than most Arthur Shield contracts. The gap narrows at true enterprise scale (100M+ events), where both require custom pricing.
Other Alternatives
Lakera Guard Alternatives
After the Check Point acquisition, many teams are evaluating alternatives. Here are the best options for every use case.
Guardrails AI Alternatives
Guardrails AI is great for output validation. If you need actual security, here are the best alternatives.
Pangea AI Guard Alternatives
AI agent security shouldn't require buying a full security platform. Here are the best standalone alternatives.
Related Resources
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