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VX
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Posted on Edited on Originally published at vznjs.github.io

See inside a run

#javascript #monorepo #devtools #opensource

Four questions, four commands. Each prints text you can read, or JSON a
script or agent can use.

Question Command
Why does this task run? vx run --affected=HEAD --dry
What did the run do? vx last --format json
What depends on what? vx run --dry=json
Where did vx spend time? VX_DEBUG_TIMING=1 vx run

Why a task runs

Edit one file in packages/a and ask what a pull request would run:

$ vx run build --all --affected=HEAD --dry
would run:
  ▶  packages/a#build  cache miss — would exec   2feaa870  ~15ms
                       affected: packages/a/src/index.ts changed (an input)
  ▶  packages/c#build  cache miss — would exec   7ed8a143  ~7ms
                       affected: packages/a/src/index.ts changed (an input), via packages/a#build

2 task(s) planned, 2 would run.
predicted: ~22ms wall · ~22ms total execution
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Each task names the changed file, or the chain that reached it.

What the run did 

$ vx last --format json | jq -c '.invocation | {command, taskCount, failedCount, hitCount, totalDurationMs}'
{"command":"vx run build --all","taskCount":4,"failedCount":0,"hitCount":4,"totalDurationMs":9}
$ vx last --format json | jq -c '.tasks[0] | {project, task, status, durationMs, hash}'
{"project":"packages/d","task":"build","status":"cache-hit","durationMs":0,"hash":"9f1cef08a2fd4006"}
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vx last --list --format json lists recent runs, newest first.

What depends on what 

$ vx run build --all --dry=json \
    | jq -r '"digraph G {", (.tasks[] | .id as $t | .deps[] | "  \"\(.)\" -> \"\($t)\""), "}"'
digraph G {
  "packages/a#build" -> "packages/c#build"
}
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Pipe it into dot -Tsvg.

Where vx spends time

diagram

VX_DEBUG_TIMING=1 vx run build --all, fastest of 7 · demo workspace · vx 22f6eb7 · 2026-10-23

VX_DEBUG_TIMING=1 prints this table for any run. A slow config or a
slow cache lookup stands out at once.

Every flag: CLI reference. The run JSON's fields:
Built for agents. More at
vznjs.github.io/vx.

Originally published on the vx blog. vx is open-source (MIT) task orchestration with a build cache: vznjs.github.io/vx · GitHub.

Written with AI assistance.

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