Rune vs Prompt Armor: AI Security Platforms Compared
Cloud API scanner vs framework-native runtime security with tool awareness
Prompt Armor and Rune both focus on protecting AI applications from prompt injection, but they differ in architecture. Prompt Armor is a cloud API that analyzes text for injection attempts — you send text and get back a classification. Rune embeds directly into your agent's framework, scanning inputs, outputs, tool calls, and inter-agent communication inline.
Prompt Armor specializes in prompt injection detection with a focus on indirect injection — malicious instructions hidden in data sources like documents, emails, and web pages that agents retrieve. They've published research on indirect injection techniques and built their detection around this threat.
Rune takes a broader approach: prompt injection is one of multiple threat categories it detects, alongside data exfiltration, credential exposure, tool manipulation, and policy violations. Rune also scans at the tool call level, which Prompt Armor's text-based API doesn't cover.
Rune
Rune is a runtime security SDK for AI agents. It wraps your LLM client and framework, scanning every input, output, tool call, and inter-agent message. Multi-layer detection covers prompt injection, data exfiltration, credential exposure, tool manipulation, and policy violations. Includes a real-time dashboard.
Prompt Armor
Prompt Armor is a cloud API focused on detecting prompt injection, particularly indirect injection in retrieved content. You send text to their API and receive a risk classification. They've published research on indirect injection techniques and specialize in detecting malicious instructions hidden in documents, emails, and web content. Prompt Armor supports integration via REST API and has SDKs for common languages.
Feature-by-Feature Comparison
Detection
| Feature | Rune | Prompt Armor |
|---|---|---|
| Direct prompt injection | Pattern + semantic + LLM judge | ML classifier specialized for injection |
| Indirect prompt injection | Scans retrieved content and tool results | Specialized in indirect injection detection |
| Tool call scanning | Scans tool parameters and results | Text-only API — no tool awareness |
| Data exfiltration detection | URL, PII, and credential scanning | Focused on injection, not exfiltration |
Architecture
| Feature | Rune | Prompt Armor |
|---|---|---|
| Integration approach | Framework-native SDK wrappers | REST API calls |
| Latency | Sub-20ms local scanning (L1/L2) | Cloud API round-trip per request |
| Framework integrations | LangChain, OpenAI, Anthropic, CrewAI, MCP | Generic REST API — manual integration |
Operations
| Feature | Rune | Prompt Armor |
|---|---|---|
| Monitoring dashboard | Real-time event stream and alerts | API usage metrics |
| Policy engine | YAML policies with configurable actions | Threshold-based configuration |
When to Choose Rune
Broader threat coverage beyond injection
Rune detects prompt injection, data exfiltration, credential exposure, tool manipulation, and policy violations. Prompt Armor specializes in injection detection only.
Framework-native integration
Rune wraps your existing client with one line of code. Prompt Armor requires you to add API calls at each point where you want scanning — more code, more maintenance.
Tool call and agent scanning
Rune sees everything your agent does — tool calls, function parameters, inter-agent messages. Prompt Armor only analyzes text you send to their API.
When to Choose Prompt Armor
Deep specialization in indirect injection
Prompt Armor has published research specifically on indirect prompt injection and built their detection around this threat vector. If indirect injection in retrieved documents is your primary concern and you want a specialist, Prompt Armor has deep expertise.
Language-agnostic REST API
Prompt Armor's REST API works with any language or framework. If you're not using Python or need to protect non-Python applications, their API approach is more flexible.
Best For
Choose Rune if...
Python agent teams that need comprehensive security scanning across multiple threat types with framework-native integration and operational dashboards.
Choose Prompt Armor if...
Teams specifically focused on indirect prompt injection detection who need a language-agnostic API and want a vendor specializing in this one threat.
Frequently Asked Questions
Is Prompt Armor better at detecting indirect injection?
Prompt Armor has deep specialization in indirect injection. Rune also detects indirect injection through its multi-layer pipeline and scans retrieved content and tool results. For most teams, Rune's broader coverage is more practical — you rarely face injection without also needing exfiltration and tool abuse protection.
Can I use Prompt Armor with LangChain or CrewAI?
Prompt Armor is a REST API, so you'd need to add API calls manually in your LangChain chains or CrewAI workflows. Rune provides native framework integrations (ShieldMiddleware, shield_crew) that require no changes to your agent logic.
Which is cheaper for high-volume scanning?
Rune's L1/L2 scanning runs locally at near-zero marginal cost per event. Prompt Armor charges per API call. For high-volume agents making many interactions per session, Rune's architecture is typically more cost-effective.
Does Prompt Armor have a free tier?
Prompt Armor offers limited free access. Rune's free tier includes 10,000 events per month — enough to secure several agents in development and early production.
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