UserPromptSubmit / beforeSubmitPrompt

This hook fires when you press Enter — before the agent has processed your message.

Agent	Hook name
Claude Code	`UserPromptSubmit`
Cursor	`beforeSubmitPrompt`

What kiteguard checks

Check	Description
Prompt injection	Patterns like "ignore previous instructions"
PII detection	SSN, credit cards, emails, phone numbers, passport IDs

Hook payload

Claude Code:

{
  "hook_event_name": "UserPromptSubmit",
  "prompt": "Summarize these customer records: Alice, SSN 123-45-6789…"
}

Cursor:

{
  "hookEventName": "beforeSubmitPrompt",
  "prompt": "Summarize these customer records: Alice, SSN 123-45-6789…"
}

Verdicts

Condition	Exit code	Effect
No match	`0`	Agent receives the prompt
Injection pattern matched	`2`	Request blocked, user sees error
PII matched + `block_on_prompt: true`	`2`	Request blocked
PII matched + `block_on_prompt: false`	`0`	Audit logged, agent proceeds
kiteguard crashes	`2`	Fail-closed

When to set `block_on_prompt: true`

Enable this if your organization's policy prohibits the agent from ever processing PII. Appropriate for environments where only anonymized data should be processed.

Disable it (the default) if users legitimately work with data that may contain PII and you only want to prevent PII from leaking out through the response.

Audit log entry

{
  "ts": "2026-03-28T10:23:01.123Z",
  "hook": "UserPromptSubmit",
  "verdict": "block",
  "rule": "pii_ssn",
  "reason": "SSN pattern matched in prompt",
  "input_hash": "a3f1c2…"
}

kiteguard