A neutral, sourced look at two AI security vendors that often come up in the same evaluation. Both protect how organisations use AI, but they are positioned differently. Here is a fair side-by-side based only on public information, plus an honest note on where a third option fits.
This is a vendor-vs-vendor comparison, not a sales page for either one. Every claim below is drawn from each company's own materials and reputable public sources.
We have kept the table even-handed, used neutral language for both, and avoided putting a thumb on the scale. Aona AI publishes this page and appears later as a clearly-labelled third option, so you have the full context. Capabilities and ownership change, so confirm the current details with each vendor before you decide.
A fair, sourced comparison across the dimensions that matter most in an AI security evaluation. Neither column is ranked above the other.
| Dimension | Prompt Security | Harmonic Security |
|---|---|---|
| Primary positioning | Broad GenAI security platform spanning employees, homegrown AI apps, AI code assistants, and agentic AI. | AI data protection and governance focused on what employees and agents send to AI tools. |
| Shadow AI discovery | Discovers AI tools in use and dynamically detects emerging AI components across web apps and the browser. | Day-one inventory of AI tools in use; states coverage of 1,000+ AI surfaces. |
| Data leakage prevention | Sanitises and redacts sensitive data (PII, PHI, financial, source code) before it reaches an LLM. | Model-based detection of sensitive data in context, moving beyond regex pattern matching. |
| Real-time response | Blocks prompt injection, jailbreaks, and data exfiltration in real time; alerts on policy triggers. | Per-policy choice to block in real time, warn the employee with context, or log silently. |
| Application & agent security | Protects homegrown LLM apps and AI code assistants (e.g. GitHub Copilot); MCP security for agents. | MCP Gateway intercepts agent traffic to discover servers/clients and enforce policy. |
| Deployment model | Delivered as SaaS or self-hosted / on-premises; positions deployment as fast. | Browser extension, desktop client, and MCP gateway; rollout via Intune, JAMF, Kandji, or GPO. |
| Ownership & stage | Acquired by SentinelOne (acquisition completed September 2025); now part of the Singularity platform. | Independent startup founded in 2023; raised a $17.5M Series A led by Next47 in October 2024. |
Sources: prompt.security and harmonic.security (vendor sites); SentinelOne's acquisition of Prompt Security completed September 2025; Harmonic Security's $17.5M Series A led by Next47, October 2024. Verify current details with each vendor.
There is no single winner here. The better fit depends on what you are actually trying to solve.
Teams that want one platform to cover not just employee AI usage but also homegrown LLM applications, AI code assistants, and agentic systems, and that are open to the SentinelOne ecosystem, tend to look here first.
Teams whose top priority is AI data protection at the point of use, with model-based detection and flexible block / warn / log responses rolled out through standard endpoint tooling, tend to look here first.
Map your real driver. If it is broad GenAI and application-and-agent security, weigh Prompt Security. If it is focused, context-aware data protection across AI surfaces, weigh Harmonic. Then pilot against your own AI traffic before committing.
If your real goal is to change how employees use AI, not just inspect traffic, it is worth weighing Aona alongside Prompt Security and Harmonic. Aona focuses on Workforce AI Security at the browser and endpoint: shadow AI discovery, DLP for AI tools, real-time coaching at the moment of a risky prompt, governance, and AI upskilling so behaviour improves over time.
Shown for transparency: Aona AI publishes this comparison. The table above is kept neutral regardless.
Pilot the option that matches your real driver. If Workforce AI Security is the gap, book a demo to see shadow AI discovery, real-time coaching, and DLP for AI tools, or start a 30-day free trial. No credit card required.