Vercel Preview Logs

Vercel Preview Logs

Use this skill to close the deploy-debug loop by fetching real Vercel preview logs from CLI and summarizing actionable failures.

When to Use

Trigger this skill for requests like:

• "check Vercel preview logs"
• "why did this preview deployment fail?"
• "inspect deployment <url/id>"
• "find logs for this PR/commit/branch deployment"

Prerequisites

• vc (Vercel CLI) is installed.
• Auth is available via VERCEL_TOKEN (preferred) or existing CLI login.
• If sandbox blocks network or home-directory writes, rerun with sandbox_permissions=require_escalated.

Wrapper Script

Use the bundled wrapper for all commands:

bash <skill-dir>/scripts/vc_safe.sh <vc-subcommand> [args...]

What it does:

• sets VERCEL_DISABLE_AUTO_UPDATE=1
• sets NO_UPDATE_NOTIFIER=1
• sets XDG_CACHE_HOME to /tmp by default
• uses -Q /tmp/.vercel-global so CLI does not need to write in ~/Library/...

Core Workflow

1. Identify the deployment

If URL/ID is provided:

bash <skill-dir>/scripts/vc_safe.sh inspect <url-or-id> --format=json -t "$VERCEL_TOKEN"

If not provided, list recent deployments for the linked project:

bash <skill-dir>/scripts/vc_safe.sh list --format=json --status ERROR,BUILDING,READY -t "$VERCEL_TOKEN"

Optional filters:

bash <skill-dir>/scripts/vc_safe.sh list --format=json -m githubCommitRef=<branch> -t "$VERCEL_TOKEN"
bash <skill-dir>/scripts/vc_safe.sh list --format=json -m githubCommitSha=<sha> -t "$VERCEL_TOKEN"

2. Fetch build logs

bash <skill-dir>/scripts/vc_safe.sh inspect <url-or-id> --logs -t "$VERCEL_TOKEN"

3. Fetch runtime logs (for READY deployments)

bash <skill-dir>/scripts/vc_safe.sh logs <url-or-id> --format=json -t "$VERCEL_TOKEN"

Output Requirements

Report:

• deployment URL/ID and state (READY, ERROR, etc.)
• the first concrete failure signal (file path, line, stack frame, or command)
• likely root cause in one sentence
• minimal fix recommendation with exact file(s)

If multiple failures exist, prioritize:

1. compile/type errors
2. missing env/config
3. runtime exceptions

Boundaries

• This skill is for diagnosis and log inspection, not deployment actions.
• Do not fabricate root causes when logs are inconclusive; report uncertainty.
• Do not leak credentials or raw sensitive values from logs.

Verification

Before finalizing diagnosis:

• verify deployment identifier and state from CLI output
• verify at least one concrete log signal supports the root-cause statement
• include exact command(s) used for traceability

Notes

• This skill focuses on inspection and diagnosis, not deploying.
• If user asks to create/redeploy previews, use vercel-deploy.

Sibling skills

Vercel/React stack — this skill is the diagnose action paired with vercel-deploy.

• vercel-deploy — paired action. Common upstream cause of the logs inspected here.
• diagnose — generalist debugging discipline. Use this skill first to gather Vercel-specific log evidence; hand off to diagnose for the broader feedback-loop framing if the bug isn't surface-level.
• nextjs-app-router, vercel-react-best-practices — referenced when log diagnosis surfaces App Router / React performance issues.