# Trailblaze > Use when working with Trailblaze — natural-language device control for coding agents across iOS, Android, and web, with replayable `.trail.yaml` files as the artifact. Trigger on mentions of Trailblaze, the `trailblaze` CLI, `.trail.yaml` files, trailmaps, waypoints, or requests to drive / author / debug / run UI tests on iOS / Android / web — including authoring a custom typed scripted tool, composing an agent's tool surface, or writing a trailmap. - Skill: `block/trailblaze` (Agent Skill, multi-file: 6 files) - Install (CLI): `npx skillmds@latest add block/trailblaze` - Raw SKILL.md: https://api.skillmd.com/api/skills/block/trailblaze/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: block (https://skillmd.com/u/block) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/block/trailblaze --- # Trailblaze **Natural-language device control for your coding agent — across iOS, Android, and web. Every session is a replayable trail you can run as a test.** Trailblaze gives your coding agent a single, typed, replayable way to drive any device. Built-in primitives plus your own typed tools, with a natural-language source of truth that travels across platforms. Whether you're exploring an app, automating a workflow, or building a test suite, the artifact is the same: a portable `.trail.yaml` whose recorded steps your CI can replay deterministically with no LLM at runtime. ## What you get - **Composable, replayable device control for your agent.** Your coding agent drives the device through Trailblaze's primitives — plus first-class commands of your own, like `login` or `addToCart`, defined in a typed language with type-safe bindings. Each step records its objective. The resulting `.trail.yaml` is both a natural-language source of truth — *what* you're testing or doing — and a deterministic execution artifact — *how* it runs. One trail can describe a flow across iOS, Android, and web — same natural-language steps, platform-specific actions or tools captured for each. Agents read the what; the framework handles the how. - **A cross-platform Trace Viewer.** Open any session — yours or your agent's — and inspect view hierarchy, screenshots, video, and platform logs at every step. When you want a different selector than the one Trailblaze auto-picked for a step, the viewer lets you choose from generated alternatives computed against the same captured hierarchy — human judgment, no re-recording. Same viewer for iOS, Android, and web. ## Native fidelity on every platform Most multi-platform testing tools expose the *intersection* of what iOS, Android, and web can do — a generic API that maps onto all three, at the cost of losing platform-specific capability. Trailblaze takes the opposite approach: full-fidelity native semantic surfaces, OS-native primitives, and typed tool sets composed per `(target, platform)`. Your agent works against each platform's native UI tree — the accessibility tree on Android, native UI semantics on iOS, the DOM on web — rather than a flattened cross-platform abstraction. The agent picks elements semantically — "the Sign in button" — from the native hierarchy. Trailblaze computes the platform-specific selectors behind the scenes. The natural-language test stays the same; the execution uses each platform's full power. This only works because an agent is driving. Exposing full native fidelity to a human is overwhelming — twenty platform-specific selector strategies per element is no one's idea of a good testing SDK. Exposing it to an LLM is the point. The agent handles the complexity; you get the expressive power of native automation with the consistency of a single natural-language test. ## The two routing keys: device and target Before you drive anything, know the two routing keys — they're the foundation every rung's commands build on: - **Device** — a connected runtime instance. The device specifier format is `/` (e.g. `android/emulator-5554`, `ios/E5BDD6FB-…`, `web/playwright-native`). Most commands accept either the full `/` form or just `` when only one device of that platform exists. `trailblaze device list` prints each connected device embedded in a copy/pastable example, like `trailblaze snapshot --device android/emulator-5554 (…) — …`, so the right `--device` argument is ready to paste into subsequent commands. - **Target** — the app context being driven. This is the **discovery surface for app-specific tools**: a trailmap published for an app (e.g. ``, or any app-specific trailmap your team ships) exposes its custom typed tools through that target. `default` is the universal target — what you use when you're not exercising a specific app's vocabulary. Many commands accept `--target ` (or `-t `) in addition to `--device`. If a target is configured at the workspace level (in `trailblaze.yaml`), commands pick it up automatically; you only pass `--target` explicitly when you want to override or when running against multiple targets in parallel. ## The three rungs — and which reference to load Trailblaze is structured as an adoption ladder. Tools you add to your agent's surface become first-class commands the next time your agent drives a device. Most teams get value at rung 1, climb to rung 2 once a flow is worth committing, and reach rung 3 when their agent has a real app vocabulary to compose. Each rung has its own deep reference; load whichever matches the task at hand. 1. **Drive a device.** Point your coding agent at the Trailblaze CLI. Natural-language device control across iOS, Android, and web — through built-in primitives plus any custom tools your team has shipped. → **Load [`references/drive-device.md`](references/drive-device.md)** when the task is to explore an app, take a UI action, see what's on screen, or discover the verbs available on a connected device. Covers `device list`, `snapshot`, `tool`, `toolbox`, the basic loop, and recoverable failure modes. 2. **Save and replay.** Any session becomes a `.trail.yaml` — replay it ad-hoc, commit it to your repo as a CI regression test, or open it in the Trace Viewer to see exactly what happened. Same artifact, three uses, no LLM at replay. → **Load [`references/save-and-replay.md`](references/save-and-replay.md)** when the task is to save a trail, replay one, run a suite, inspect a session (HTML report or desktop trace viewer), or look up the results of a past CI run. Covers `session save`, `run` (and its `--self-heal` / `--memory` / `--secret` flags), `report`, `app`, and `results show`. 3. **Compose your own agent surface.** Give your agent first-class commands like `login` or `addToCart`, named waypoints for your screens, and trailmaps from other teams. Curate exactly what your agent sees: surface your `login` and hide the low-level taps; pick four of twenty primitives if that's what your tests need. Custom commands are typed and type-safe, with IDE support, replayable capture, and LLM-facing descriptions written for the tool and each parameter — your agent reads those descriptions to decide when and how to call them. Every call — yours, theirs, or built-in — is a first-class command, recordable and replayable. → **Load [`references/compose-agent-surface.md`](references/compose-agent-surface.md)** when the task is to author a typed scripted tool, define a waypoint, curate which tools the agent sees, write a `trailmap.yaml`, or debug "my custom tool isn't showing up in `toolbox`". Covers `trailblaze.tool(handler)` authoring, sibling YAML descriptors, trailmap composition via `dependencies:`, and the four-checkpoint workflow for diagnosing a missing tool. ## Companion mode An agent-attached authoring session: your coding agent is the single writer of a trail folder's files, and Trail Runner opens a read-only live view of that folder for the human to watch and steer. Start one with `trailblaze companion start --folder --title "" --agent claude|codex`, then tail what the human does with `trailblaze companion listen `. Steer the window with standing directives - `banner`, `checklist`, `actions` (quick-reply chips), `select-app-target`, `select-device`, `arm-recording`, and the one-shot `navigate`. Each is latest-per-name state that survives window reloads; re-send one with no fields to retract it. **Single-writer rule:** the UI never writes trail files back. A human "Save" click or a guided recording both go through the daemon, which writes the file and then tells every listening session about it. Two events matter most on the listen stream: - **`recording-saved`** - a recording landed in your folder, whether from a companion save or Trail Runner's own board record flow; it fans out to every companion session watching that folder, not just the one that wrote it. - **`run-started` / `run-finished`** - a human ran a trail from Trail Runner's UI whose path is inside your folder; both carry the run's `sessionId` and your `folder`, and `run-finished` adds `status: succeeded|failed|cancelled`. Only Trail Runner's own run endpoints announce, and only for primary-root trail/bundle ids - a raw-YAML replay (e.g. via MCP) bypasses that dispatch seam and stays silent. Shared-brain requests: if the human clicks "Review my trail" (or asks for proposed steps) in Trail Runner while your listen stream is open, the daemon queues the ask on you instead of calling its own LLM - watch for a `human_action` event titled `agent-request` with `{requestId, kind, payload}` (kind `review-trail` or `propose-steps`). Do the review by editing the trail folder's files yourself, then settle it with `trailblaze companion respond --request --status done|error`. A request you never answer is cancelled when the session ends. Companion journals (`.companion/journal-.jsonl`) age out after 7 days, swept the next time a session connects to that folder - never at disconnect, since a crashed agent resuming with `--after` needs its own journal. `trailblaze companion --agent-help` prints the full event and directive contract; load that instead of guessing at the wire format. ## Self-heal Recorded trails replay deterministically by default — no LLM in the loop, no flake. When a recorded step genuinely doesn't match the screen anymore, there are two repair paths: - **Built-in self-heal handles small drift** — text changes, an unexpected popup, a minor reorder within an established flow. Opt in with `--self-heal` and Trailblaze's built-in agent patches the failing step against the live screen. - **Your coding agent handles the larger cases** — anything that needs project context, log inspection, or judgment calls about intent. The trace session (view hierarchies, screenshots, video, platform logs, the trail YAML itself) is the diagnosis surface. You read the trace, compare what the step intended (its natural-language objective) to what the app now does, and propose a fix. The user reviews and commits. The natural-language objectives are what make this work. They tell you *what the step was trying to do*, so repair is a matter of updating the *how* against the current app — not re-deriving intent from a broken selector. ## Built for an evolving ecosystem The AI agent ecosystem is moving fast. Whatever it looks like in a year — or five, or ten — natural-language tests will come with the user. Trailblaze captures *what* is being tested as portable prose; the *how* (selectors, recordings, agent harness, framework version) adapts as the landscape changes. --- When any rung in this skill drifts from the CLI — *or* when this skill is restructured (new reference file, rung added, cross-link moved) — the sibling `trailblaze-validate-oob` skill encodes the methodology for catching it: fresh-context subagent, real installed binary, scenario per rung. Re-run it any time the CLI changes, after any non-trivial skill edit, or about once a month otherwise. If validate-oob surfaces a gap, the default fix is **update the CLI to match the skill** (rather than rewriting the skill to match a quirky CLI) — the skill encodes the surface we want users to see; the CLI should grow toward it. ## What Trailblaze is not Trailblaze is not a full coding agent. It ships a functioning agent focused on the natural-language step it's currently executing, with vision into the current screen and past steps — fine for many flows. What it doesn't try to be is a Claude Code, Cursor, or Codex: those have the user's entire codebase in context, can query logcat at runtime, and bring far more project context to bear. For serious authoring work, those agents drive Trailblaze. And Trailblaze is not a SaaS test platform — the trail YAML lives in the user's repo, they own it, they can read and edit it.