The Developer-Friendly Arthur Shield Alternative for AI Agent Security
Arthur Shield is enterprise-only with heavy integration overhead. Rune gives you production-grade security in 3 lines of code.
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 Rune Solves These 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.
Quick Comparison
| Feature | Rune | Arthur Shield |
|---|---|---|
| Pricing model | Free 10K/month, then $0.05/1K scans — self-serve | Enterprise contracts ($25K+ annually) |
| Setup time | 3 lines of code, under 5 minutes | 2-6 weeks (procurement + integration + professional services) |
| Agent framework support | LangChain, OpenAI, Anthropic, CrewAI, MCP, OpenClaw | Generic API validation — no framework awareness |
| Product focus | Purpose-built for agent security threats | Model monitoring platform with security add-on |
| Latency overhead | 4-8ms median (local scanning) | Variable — cloud API with monitoring pipeline |
| Data privacy | Local-first — raw content stays on your infra | Cloud processing required for all validation |
| Custom policy engine | YAML policies (tool restrictions, rate limits, custom rules) | Fixed built-in rulesets only |
| Hallucination detection | Not supported (security-focused) | Yes — core Arthur AI capability |
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
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 Alternative
Lakera Guard was acquired by Palo Alto Networks and shifted enterprise. Rune is the independent, developer-first alternative.
Guardrails AI Alternative
Guardrails AI validates outputs. Rune secures the entire agent pipeline — inputs, outputs, tool calls, and inter-agent communication.
Pangea AI Guard Alternative
Pangea bundles AI scanning into a broad security platform. Rune is purpose-built for the specific threats AI agents face.
Related Resources
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