studio

weft studio — the Inspector

A read-only UI over a run store: the runs list, the run page (steps, tool calls and results, subagents inline, truncation badged), guaranteed replay over the event index, raw JSON, and agent and tool cards from the manifest. One http.Handler, no build step for users, fully offline.

Use it

mux.Handle("/studio/", http.StripPrefix("/studio",
    studio.Handler(myStore, studio.Manifest(manifestBytes)))

Then record runs with store.Record (see examples/basic) and open http://127.0.0.1:7331/studio/. Try the example end to end:

go run ./studio/examples/basic        # records three demo runs, serves :7331
go run ./studio/examples/basic -serve # serve an existing database only

The runs list (light): status as a dot and a word, the error under a failed run's id, filters that mirror the URL, the whole row opens the run:

The run page (light) — the prompt and the answer first, then the facts and the replay bar; below, the trace: the flow strip (one pill per step, arrows for results fed back), then the waterfall on the left — the run, its steps, tool calls and subagent runs (their own steps and calls nested) as spans on one axis — and the selected span's data on the right, read as detail (the same step and call bodies as the story), events (only that span's slice of the stream) or json (the folded node). The trace opens on whatever went wrong, else the first step; j/k or the arrow keys walk it; ?sel= names the selection. The split appears when the content is about 768px wide (collapse the sidebar on a small screen), and the toggle beside the flow strip forces side by side or stacked:

The axis is the event position: events carry no timestamps, so this is order, not duration (T2a's spans put time on the same component). Scrubbed to event 6 of 14, the replay playhead crosses every row, everything past it is veiled, and the detail panel renders the fold at the playhead — the call reads running until its finish is revealed:

A failed run (dark): the error at the top, the flow strip's step 1 red, the ORDER_NOT_FOUND tool error as data (mustard, never red) selected first, and the step that had no step_finish saying so:

The story view (s) is the step cards top to bottom, the same bodies as the detail panel:

Raw (light) — the events explorer: every event by position with its kind, type and a one-line summary, filtered by kind, searched by any JSON text, opened to the full event, and sent to the replay playhead with one click. The document surface is the run document as a collapsible tree; both copy and download whole:

Replay (dark), scrubbed to event 6 of 14 — the readout names the event at the playhead, the steps show exactly the folded prefix, and a call without its finish yet reads running…:

Dark and light follow the system; the sidebar footer's toggle (or the palette) cycles system → light → dark:

Every view is a URL: filters, view=story|raw (and raw=doc), the selected span sel and detail mode d, the selected step, and the replay position t all live in search params — paste a link into an issue and it reproduces exactly. Keyboard: ⌘K jumps to any recent run, / filters, j/k move (rows in the list, spans in the trace), enter opens, e/s/r switch trace/story/raw, space replays, [/] jump by step or tool event, ,/. move one event, ? lists everything, g r/g a navigate. Keys fire only on a bare press outside a text box — ctrl/⌘ always go to the browser.

The API (plan §3 of docs/phase2b-studio-plan.md)

Read-only JSON under {base}api/: meta (versions, capabilities), runs (list, filtered, paged by cursor), runs/{id} (the run document — never events), runs/{id}/events?after=&limit= (the paged event stream; a live tail is the same endpoint read from the last position), manifest. Capabilities are the hosting seam (ADR 0018 §8): the open handler reports none; a hosted server declares them with studio.Capabilities(…).

Contributing to the UI

The web app lives in web/ — TanStack Start in SPA mode, React, shadcn/ui on Tailwind v4, built with Bun. Users never need it: the build output is committed at dist/ and embedded with go:embed.

make studio-build   # cd studio/web && bun install && bun run build
make studio-check   # rebuild, prove dist is fresh, check the 600 KiB gzip budget, typecheck + test

make studio-check is the freshness gate (ADR 0018 §4): it fails if dist/ does not match web/ or if the gzipped total exceeds 600 KiB (currently ~313 KiB). The build is deterministic — two builds from one tree are byte-identical (scripts/clean-dist.ts pins the router's prerender timestamp and keeps <base href> first in <head>).

The dev loop is two terminals: go run ./studio/examples/basic -serve (API + embedded UI on :7331) and cd studio/web && bun run dev -- --base /studio/ (Vite on :3000 proxying /studio/api).

Go module: github.com/weftgo/weft/studio, requiring the tagged weft and weft/store — standalone-importable, no replace.