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Reading preview logs

Follow install, build, and boot logs to understand exactly what your preview is doing.

Every preview streams its logs live — the same output a developer would watch in a terminal. You don't need to be one to get value from them: knowing the phases and a few landmark lines tells you where a preview is, and where it got stuck.

The phases of a preview boot

A starting preview walks through predictable stages, and the logs announce each:

  1. Install — dependencies are restored ("Preview starting…", restore/install output). Slow the first time, fast after.
  2. Database preparation (API previews) — an ephemeral Postgres is created, migrations run, seed data loads. See Preview databases.
  3. Build — the project compiles. Warnings are usually fine; errors stop the boot here.
  4. Boot — the app starts and binds its port; the preview URL becomes active.

Once running, the logs switch to live application output: every request, and every error, as it happens.

How to read a failure

  1. Scroll to the first error, not the last. Failures cascade; the earliest one is almost always the cause and the rest are noise.

  2. Note the phase it happened in. A build error means the code doesn't compile; a database error during startup usually means migrations and schema disagree; an error after boot is an application bug.

  3. Hand it off: Analyse & Fix reads the same logs, identifies the root cause, and proposes the fix — you don't need to interpret the stack trace yourself.

Last updated: September 4, 2026