HEAD-TO-HEAD · FACTS ONLY
Harmonic vs Prompt Security: AI endpoint control facts side by side
Short answer
By The Device Desk · Endpoint AI Finder · Published 2026-10-11
Desk research from public vendor pages read on 27 September and 11 October 2026. Profiles follow our published method; we did not run the products.
Vendor pages read September and October 2026 · updated 2026-10-13
Where do their controls sit?
- Filled or hatched marker: Harmonic
- Dashed teal ring: Prompt Security, described
- DEV Filled marker: described on the product pages we read
- DEV Hatched marker: partly described (another component, a narrower scope, or method not detailed)
- DEV Dashed marker: not in our sources (it may exist; we did not find it)
What are the facts, side by side?
| Fact | Harmonic | Prompt Security |
|---|---|---|
| Owner | None | SentinelOne (acquisition announced 5 August 2025; SentinelOne's blog of 3 September 2025 is titled SentinelOne Acquires Prompt Security) |
| Positioning | A data protection product for everyday AI use, sold as Explore, Guide and Command, covering browser extensions, desktop apps and CLI tools, MCP gateways and an API. | Prompt Security, now part of SentinelOne, inventories AI tools and code assistants, including unsanctioned shadow AI, through two local sensors, a browser extension and a dedicated AI endpoint agent, and is built into the SentinelOne Singularity Platform. |
| How it reaches devices | Rolls out through Intune, JAMF, Kandji or Group Policy. Source: Harmonic Security homepage · Read 27 Sep 2026 | Two local sensors: a browser extension and a dedicated AI endpoint agent, managed from the SentinelOne Singularity Platform. Prompt Security argues that MDM or EDR integrations, which mostly run scripts periodically, are not enough. Source: Prompt Security blog: browser and endpoint sensors · Read 11 Oct 2026 |
| On-device controlDiffers | Partly describedDeployment options include desktop apps and AI agents, rolled out through device management; the on-device component is not described in detail. Source: Harmonic Security pricing (re-read) · Read 11 Oct 2026 | DescribedA dedicated AI endpoint agent detects new AI agents, skills and connectors and applies runtime policies; it names GitHub Copilot, Cursor and Claude Code among the code assistants it inventories. Source: Prompt Security blog: browser and endpoint sensors · Read 11 Oct 2026 |
| Browser extension | DescribedBrowser extensions are a listed surface, with block, warn or log actions. Source: Harmonic Security homepage · Read 27 Sep 2026 | DescribedA browser extension inspects prompts, redacts sensitive data and discovers shadow AI. Source: Prompt Security blog: browser and endpoint sensors · Read 11 Oct 2026 |
| Network or SSE proxy | Not in our sourcesNot described on the pages we read. | Not in our sourcesNot described on the pages we read. |
| AI or MCP gatewayDiffers | DescribedMCP gateways are a listed surface, and Harmonic Command governs at the MCP layer and at the tool surface. Source: Harmonic Security: Command · Read 27 Sep 2026 | Not in our sourcesNot described on the pages we read. |
| Names the coding agents it covers | MatchesThe Guide tier adds desktop AI apps and developer tools, naming Claude Code, GitHub Copilot, ChatGPT Desktop and Microsoft 365 Copilot. Source: Harmonic Security pricing (re-read) · Read 11 Oct 2026 | MatchesNames GitHub Copilot, Cursor and Claude Code. Source: SentinelOne: Prompt Security · Read 27 Sep 2026 |
| Decides on a tool call before it runsDiffers | PartlyThe Command tier adds MCP client and server discovery, agent permissions for read, write and execute, and MCP server tool controls. Source: Harmonic Security pricing (re-read) · Read 11 Oct 2026 | Not in our sources |
| Controls what goes into browser AI | MatchesBlock, warn or log on AI use in the browser. Source: Harmonic Security homepage · Read 27 Sep 2026 | MatchesThe browser extension inspects prompts and redacts sensitive data. Source: Prompt Security blog: browser and endpoint sensors · Read 11 Oct 2026 |
| Rolls out through EDR or device management you runDiffers | MatchesRolls out through Intune, JAMF, Kandji or Group Policy. Source: Harmonic Security homepage · Read 27 Sep 2026 | PartlyIts own agent and extension, managed in the SentinelOne console; it does not ride on other EDR or MDM tools. Source: Prompt Security blog: browser and endpoint sensors · Read 11 Oct 2026 |
| Can warn or ask instead of only blockingDiffers | MatchesWarn is one of three actions, with block and log. Source: Harmonic Security homepage · Read 27 Sep 2026 | Not in our sources |
| Can block an agent, tool or actionDiffers | MatchesBlock is one of three actions. Source: Harmonic Security homepage · Read 27 Sep 2026 | Not in our sources |
| Has a watch-only or simulation modeDiffers | MatchesLog is one of three actions, for watching before enforcing. Source: Harmonic Security homepage · Read 27 Sep 2026 | Not in our sources |
| Records who or what took each action | Not in our sources | Not in our sources |
| Also covers SaaS, cloud or homegrown AIDiffers | PartlyAn API is listed alongside device surfaces; SaaS or cloud agents are not described. Source: Harmonic Security homepage · Read 27 Sep 2026 | MatchesCovers homegrown AI apps from testing to runtime. Source: SentinelOne: Prompt Security · Read 27 Sep 2026 |
| Has a public price or tiers (vendor site or marketplace)Differs | PartlyNames three tiers (Explore, Guide, Command) on its pricing page, without prices. Source: Harmonic Security: pricing · Read 27 Sep 2026 | Not in our sources |
| Built into | None | Built into the SentinelOne Singularity Platform. Source: SentinelOne: Prompt Security · Read 27 Sep 2026 |
| Works with | None in our sources | None in our sources |
| Price | Three named tiers (Explore, Guide, Command) with no prices; a full prompt audit log is an add-on on Guide and Command. Source: Harmonic Security pricing (re-read) · Read 11 Oct 2026 | Not published. Source: SentinelOne: Prompt Security · Read 27 Sep 2026 |
Where do they differ?
- On-device control: Harmonic partly describes it; Prompt Security describes it.
- AI or MCP gateway: Harmonic describes it; Prompt Security is not in our sources.
- Decides on a tool call before it runs: Harmonic partly matches; Prompt Security is not in our sources.
- Rolls out through EDR or device management you run: Harmonic matches; Prompt Security partly matches.
- Can warn or ask instead of only blocking: Harmonic matches; Prompt Security is not in our sources.
- Can block an agent, tool or action: Harmonic matches; Prompt Security is not in our sources.
- Has a watch-only or simulation mode: Harmonic matches; Prompt Security is not in our sources.
- Also covers SaaS, cloud or homegrown AI: Harmonic partly matches; Prompt Security matches.
- Has a public price or tiers (vendor site or marketplace): Harmonic partly matches; Prompt Security is not in our sources.
Choose Harmonic if
- Your main risk is employees pasting sensitive data into AI tools and you would rather coach than block
- You manage devices with Intune, JAMF, Kandji or Group Policy
Choose Prompt Security if
- You already run SentinelOne Singularity
- You need an inventory of AI tools and coding assistants first
Which limits should you check?
Harmonic
- Tier names only, no prices, and the full prompt audit log is an add-on.
- An activity record that separates a person from an agent is not described, and prompt injection protection is listed as coming soon.
Prompt Security
- Two new local sensors to roll out, a browser extension and an endpoint agent, unless you already run SentinelOne.
- Tool-call decisions, blocking, warning and activity records for agent actions are not described on the pages we read, and no pricing is published.