Free vs Paid Security APIs for AI Agents scanners are free; staying current is the product.

Most security work an agent does is on your own code and traffic, where local, open-source servers are exactly right. skylos scans your repositories on your machine; wireshark-mcp analyzes captures with tshark for audits and threat hunting; MCPProxy sits in front of your other MCP servers with security scanning and quarantine, plus BM25 tool discovery that it says cuts token usage dramatically.

Local execution is a security feature in itself here: your source code and packet captures never leave your infrastructure. For this class of work, free isn't a compromise — it's the correct architecture.

A vulnerability scanner is only as good as its rules. New CVEs, new typosquatted packages, new prompt-injection patterns — tools like agent-security-scanner-mcp and shellward are in an arms race, and their value depends on continuous updates. An abandoned open-source scanner doesn't fail loudly; it quietly stops catching things.

That maintenance burden is the honest case for paid security endpoints: you're not buying the scan, you're buying the operator's commitment to keep the detection current.

Security checks slot naturally into agent workflows as discrete, billable events: scan this dependency tree, check this prompt for injection, audit this config. x402 prices each event directly — the agent receives an HTTP 402 with the price, pays in USDC, and the scan runs, settling on Base in about two seconds with an Ed25519-signed receipt. Minimum $0.01 per call, no vendor onboarding, no seat licenses.

The receipt matters more in security than anywhere else: a signed, timestamped record that a specific check ran at a specific moment is itself useful evidence in an audit trail.

Run free, local servers for anything touching your private code and traffic — that's both cheaper and safer. Consider paid, x402-priced endpoints for detection that depends on continuously updated intelligence, where the per-call fee funds the updates you're relying on. And whichever you choose, vet it: a security tool is the last place to install an unmaintained dependency.

Loomal's Security category lists all 378 live servers with descriptions and per-call pricing where configured, so the maintenance-funded options are visible next to the self-host ones.