The Full-Stack Prompt Armor Alternative for AI Agent Security
Prompt Armor detects injection. Rune secures your entire agent — inputs, outputs, tool calls, and inter-agent communication.
Why Teams Look for Prompt Armor Alternatives
Narrow scope — prompt injection only
Prompt Armor focuses exclusively on classifying text as injection or not. It doesn't detect data exfiltration patterns (encoded data in URLs), PII leaking in model outputs, secret exposure (API keys in responses), or privilege escalation through tool abuse. As agent attacks diversify, injection-only detection covers a shrinking percentage of the threat surface.
Cloud API adds 50-150ms per scan
Every scan requires sending the full prompt text to Prompt Armor's API for classification. Measured latency is 50-150ms depending on input size and region. For interactive agents making multiple tool calls per turn, this compounds into noticeable user-facing delays.
Prompts leave your infrastructure on every call
Prompt Armor's cloud classification means your raw prompts and responses are transmitted to a third-party API. For teams handling PII, financial data, or health records, this creates a data processing relationship requiring DPAs and potentially conflicting with data residency requirements.
No agent framework support or tool call awareness
Prompt Armor is a REST endpoint — you POST text, you get a classification. It has no concept of LangChain chains, CrewAI crews, MCP tool calls, or multi-step agent workflows. When an attacker injects instructions through a tool's return value, Prompt Armor can't see the tool context.
No dashboard or monitoring on lower tiers
Prompt Armor returns a classification result per API call. There's no event history, no threat analytics, no pattern detection across sessions, and no alerting. You see individual scan results but can't answer 'what attacks have my agents seen this week?'
How Rune Solves These Problems
Full-spectrum threat detection — 5+ categories
Beyond injection: data exfiltration detection (base64-encoded data in URLs, sensitive fields in tool args), PII scanning (SSN, credit card, email), secret detection (API keys, JWTs, connection strings), privilege escalation monitoring, and command injection. One platform covering the full agent threat model.
Tool call and inter-agent scanning
Rune inspects tool arguments before execution (blocking malicious file paths, SQL in tool params), tool return values (detecting exfiltrated data), and inter-agent messages (catching injection passed between agents). These are the attack surfaces that text-level APIs like Prompt Armor can't see.
Local-first — raw content never leaves your infrastructure
All scanning runs in your application process using local pattern databases and embeddings. Only structured metadata (event type, threat category, scan result) reaches the dashboard. No DPA required, no data residency concerns. Compare to Prompt Armor where every prompt is sent to their cloud.
4-8ms median latency vs. 50-150ms API round-trips
Layer 1 (regex): <3ms. Layer 2 (vector similarity): 5-10ms. Layer 3 (LLM judge): only fires for ambiguous cases (~5% of traffic). Median total: 4-8ms for 95% of requests. No network round-trip, no cloud dependency.
Real-time dashboard with alerting on every tier
Every Rune plan — including the free 10K events/month tier — includes the full dashboard with event history, threat analytics, and alerting. See attack patterns across all your agents, not just individual scan results.
Quick Comparison
| Feature | Rune | Prompt Armor |
|---|---|---|
| Threat coverage | Injection, exfiltration, PII, secrets, escalation | Prompt injection classification only |
| Architecture | In-process SDK (local scanning, metadata-only telemetry) | Cloud REST API (full text sent for classification) |
| Latency overhead (median) | 4-8ms (local regex + vector) | 50-150ms (API round-trip) |
| Tool call scanning | Scans tool inputs, outputs, and inter-agent messages | Not supported — text classification only |
| Framework integration | LangChain, OpenAI, Anthropic, CrewAI, MCP, OpenClaw | Generic REST API (manual wiring required) |
| Data privacy | Raw content stays local; metadata-only telemetry | Full prompt text sent to cloud API |
| Dashboard & event history | Real-time dashboard on all tiers (including free) | Per-call classification results only |
| Custom policy engine | YAML policies (tool restrictions, rate limits, custom rules) | Fixed injection threshold only |
You Should Switch If...
- You need protection beyond just prompt injection
- Your agents use tools and you need tool call scanning
- You can't afford to send prompts to an external API
- You need a real-time dashboard for monitoring agent threats
- You use LangChain, CrewAI, or MCP and need native integration
How to Switch from Prompt Armor to Rune
- 1Install the Rune SDK: pip install runesec
- 2Initialize Shield as middleware on your agent client
- 3Remove Prompt Armor API calls from your pipeline
- 4Configure security policies in YAML (injection detection is on by default)
- 5Verify detection with test payloads — injection and other threat types
- 6Remove Prompt Armor API keys from your environment
Frequently Asked Questions
Does Rune detect prompt injection as well as Prompt Armor?
Rune uses multi-layer detection: L1 regex (<3ms) catches known injection templates, L2 vector similarity (5-10ms) detects semantically similar attacks, and L3 LLM judge fires for ambiguous cases. This layered approach matches Prompt Armor's injection accuracy while adding data exfiltration, PII, secret, and escalation detection. For teams that only need injection detection, both are effective — Rune adds breadth that becomes critical as agent attack surfaces expand.
Is Prompt Armor's cloud API a security or compliance concern?
It depends on your data. Sending raw prompts to any third-party API creates a data processing relationship. If your agents handle PII (healthcare, finance, legal), you'll need DPAs and potentially HIPAA BAAs with Prompt Armor. Rune's local-first architecture avoids this entirely — scanning runs in your process, and only structured metadata reaches the dashboard.
What's the honest case for staying with Prompt Armor?
If your agents are simple (no tool calls, no multi-agent delegation) and prompt injection is genuinely your only threat, Prompt Armor is a solid, focused tool with continuously updated models. The case for switching to Rune strengthens when you have tool-calling agents, need broader threat coverage, care about latency under 50ms, or want to keep prompts off third-party servers.
How hard is the migration from Prompt Armor to Rune?
Straightforward. Replace your Prompt Armor API calls with Rune Shield middleware: `shield = Shield(client)` wraps your agent client and scans all calls automatically. No changes to agent logic needed. Injection detection is on by default. Then remove your Prompt Armor API keys. Most teams complete migration in under an hour.
Other Alternatives
Lakera Guard Alternative
Lakera Guard was acquired by Palo Alto Networks and shifted enterprise. Rune is the independent, developer-first alternative.
Rebuff Alternative
Rebuff pioneered multi-layer injection detection but is no longer actively maintained. Rune picks up where Rebuff left off — and goes further.
LLM Guard Alternative
LLM Guard is a solid open-source starting point. Rune is what you upgrade to for production agent security.
Related Resources
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