Causal debugging workbench

Reduce the failure. Keep the proof.

Load a browser failure, lock the condition that proves it, then let FAULTLINE minimize semantic units while preserving revision-bound evidence. The same deterministic engine is available to humans, browser APIs, and WebMCP agents.

ExecutionDeterministic

SurfaceBrowser + WebMCP

BoundarySandboxed

Load / edit case

Canonical source

Edit one source axis without losing the guarded revision history.

HTML · CSS · JS

Source editor

Canonical source editorRevision-guarded writes

Define oracle

Live experiment

Measure one deterministic failure condition inside the isolated preview.

Oracle type

Target selector

Property

Failure value

Before measurement

Action selector

Action valueUsed by “Set form value”; ignored by other action kinds.

Checked stateUsed by “Set checked state” for checkbox and radio controls.

Action sequence JSONFor “Action sequence”, provide 1–8 ordered click, set_value, set_checked, or wait steps. Wait uses {"kind":"wait","durationMs":...}; total wait time is capped at 2000 ms.

Run / reduce

Reduction frontier

Probe one unit or automatically minimize an axis while preserving the failure.

0 units detected on active axisDeterministic ddmin

Evidence / export

Causal evidence trail

Every experiment remains tied to the exact revision that was actually tested.

No experiments yet.

IntegrateBrowser API + WebMCP connection surfaceWebMCP tools

Browser API

The same canonical engine backs the UI and window.faultline. Inspect first, then load a complete case atomically or edit one axis with an expected revision.

const state = await window.faultline.inspect()

await window.faultline.loadCase({
  expectedRevision: state.revision,
  case: {
    html: '<main>...</main>',
    css: 'main { ... }',
    js: '...',
    oracle: {
      kind: 'dom_exists',
      selector: 'main',
      equals: true,
      action: { kind: 'none' }
    }
  }
})

await window.faultline.applySource({
  expectedRevision,
  targetAxis,
  source
})

WebMCP agent flow

FAULTLINE exposes the registered WebMCP tool surface. Stale writes are rejected instead of silently mixing agent and human state.

faultline_inspect
  ↓
faultline_load_case({
  expectedRevision,
  case
})
  ↓
faultline_define_oracle
  ↓
faultline_run
  ↓
faultline_probe
  ↓
faultline_reduce
  ↓
faultline_autopilot
  ↓
faultline_history / faultline_export