aspex simulate

Counterfactual security analysis: what would happen to your attack surface if you changed something. Nothing is modified.

aspex simulate --remove-server playwright
aspex simulate --restrict-filesystem filesystem=~/projects/acme
aspex simulate --deny-network '*'
aspex simulate --remove-tool desktop-commander.start_process

simulate clones your environment in memory, applies a hypothetical change, recomputes capabilities and attack paths through the same pipeline as a real scan, and compares before with after. Your configuration is never touched; the last line of every run says so.

What you can change

Flag	Effect
--remove-server NAME	drop a configured server
--restrict-filesystem [SERVER=]ROOT[,ROOT]	replace a filesystem server’s allowed roots (omit SERVER= for every filesystem server)
--deny-network [SERVER|*]	remove network egress, as an allowlist of nothing would
--remove-tool SERVER.TOOL	drop one tool from a live tool list
--remove-hook EVENT	remove lifecycle hooks for an event
--remove-skill NAME	remove a skill

Flags are repeatable and combine, so you can evaluate a whole hardening change at once.

Output

$ aspex simulate --restrict-filesystem filesystem=~/projects/acme

  ◆  Security impact simulation
     • restrict filesystem to ~/projects/acme

  BEFORE   blast radius HIGH   6 attack path(s)
  AFTER    blast radius MEDIUM 2 attack path(s)

  REMOVED ATTACK PATHS
     ✓ Potential sensitive data exfiltration path  CRITICAL · filesystem + playwright
     ✓ Potential persistent agent compromise path  CRITICAL · filesystem + brave-search

  SEVERITY CHANGED
     ~ Potential sensitive data exfiltration path (filesystem + github): HIGH → MEDIUM

  Capability changes
     ~ filesystem  roots /Users/you → /Users/you/projects/acme

  No configuration was modified.

--json emits the versioned aspex-simulate/v1 schema: before/after environments, capability deltas, and attack paths added and removed.

Where simulation shows up elsewhere

• aspex explain "…" ends every YES answer with the controls that break the path, each simulated so you see which one removes it on its own.
• aspex tighten runs each recommendation through the simulator and shows its security impact next to the functional impact.
• aspex inspect <command|path> simulates adding a server you have not installed yet.
• aspex mcp exposes aspex_simulate_change so your coding agent can check a proposed .mcp.json before it writes it.

All four share this one engine, so the numbers agree everywhere.