# Compare Generations

Compares two `tuist generate` runs to identify cache hit rate changes and root-cause...

- Repository: https://github.com/tuist/tuist (5859 stars)
- Category: Engineering
- License: see repository
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add tuist/tuist --skill compare-generations -g -a claude-code -y`
Codex: `npx skills add tuist/tuist --skill compare-generations -g -a codex -y`
Cursor: `npx skills add tuist/tuist --skill compare-generations -g -a cursor -y`
Gemini CLI: `npx skills add tuist/tuist --skill compare-generations -g -a gemini-cli -y`

## Description

Compares two `tuist generate` runs to identify cache hit rate changes and root-cause analysis of cache invalidation. Can be invoked with generation IDs, dashboard URLs, or branch names.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Compare Generations

## Quick Start

You'll typically receive two generation identifiers. Follow these steps:

1. Run `tuist generate list --json` to find generations on each branch.
2. Run `tuist generate show <id> --json` for both base and head generations.
3. Compare duration, status, and cache hit rates.
4. Summarize cache changes with root cause analysis.

## Step 1: Resolve Generations

### If base/head are generation IDs or dashboard URLs

Fetch each directly:

```bash
tuist generate show <base-id> --json
tuist generate show <head-id> --json
```

### If base/head are branch names

List recent generations on each branch:

```bash
tuist generate list --git-branch <base-branch> --json --page-size 1
tuist generate list --git-branch <head-branch> --json --page-size 1
```

Then fetch full details with `tuist generate show <id> --json`.

### Defaults

- If no base is provided, use the project's default branch (usually `main`).
- If no head is provided, detect the current git branch.

## Step 2: Compare Top-Level Metrics

After fetching both generations, compare:

| Metric | What to check |
|---|---|
| `duration` | Flag if head is >10% slower |
| `status` | Flag if base succeeded but head failed |
| `cacheable_targets` | Note if target count changed |
| `local_cache_target_hits` | Compare local hit counts |
| `remote_cache_target_hits` | Compare remote hit counts |
| `is_ci` | Note if one is CI and the other local |

Compute cache hit rates:
- Base: `(local_hits + remote_hits) / cacheable_targets * 100`
- Head: same formula
- Delta: `head_rate - base_rate`

## Step 3: Analyze Cache Invalidation

If cache hit rate dropped, the key question is: **which target(s) caused the invalidation cascade?**

The rest: https://github.com/tuist/tuist/blob/HEAD/skills/skills/compare-generations/SKILL.md