Threat model and limitations

Useful evidence. Never a safety guarantee.

Tripwire is a deterministic inspection layer for known prompt-injection patterns. It supports human review and stronger policy controls.

The current engine should not be the only control protecting an autonomous agent. A clean result means no known rule matched, not that the content is safe.

System boundary

Tripwire Inspect processes user-chosen selected text, visible main-frame page text and, in Deep DOM mode, hidden text, comments, structured data and text-bearing attributes. It deliberately excludes form-field values and passwords.

Inspect is a browser-side signal detector. Core provides the same typed detector to the command line. Guard exposes the detector as a local stdio MCP tool; the connected host remains responsible for enforcement at dangerous action sinks.

Known detection coverage

The versioned ruleset checks deterministic signals associated with common injection and exfiltration patterns.

  • Instruction overrides, fake roles and jailbreak phrasing.
  • Secret solicitation and sensitive-data exfiltration.
  • Clearly dangerous shell activity and confirmation bypass.
  • Safety-control bypass and evidence removal.
  • Invisible Unicode, compatibility characters, scrambled instruction words and explicit encoded payloads.

Known gaps

  • Novel semantic paraphrases, unsupported languages, homoglyphs and sophisticated encodings.
  • Attacks that require user-goal, identity, conversation, provenance or later tool-call context.
  • Instructions present only in images, audio, video, PDFs, cross-origin frames or agent-specific reader APIs.
  • Adaptive attacks designed against the public ruleset.

How to read a decision

Allow
No known rule matched. This is not a safety certificate.
Review
A suspicious signal or source context needs human judgment.
Recommend block
A high-severity known pattern matched. Enforcement still belongs inside the agent or policy layer.
Signal score
A deterministic heuristic, not a probability or calibrated risk estimate.

Required companion controls

Production agents should combine content inspection with source-aware policy enforcement.

  • Least privilege and narrowly scoped tools.
  • Origin restrictions, sandboxing and source provenance.
  • Outbound URL controls and tool-argument validation.
  • Human confirmation for consequential actions.
  • Auditable logs, adversarial evaluation and incident response.

Validation status

The repository includes a 43-case behavior regression corpus, a balanced 100-case public evaluation and 28 automated tests. The evaluation currently reports 85.0% accuracy, 83.0% precision, 88.0% recall and 82.0% specificity.

It is not an independent benchmark. The complete confusion matrix, known misses and machine-readable results are published on the evaluation page.