# Show HN: Diff Glance – CLI that turns a Git diff into a summary and a diagram

> Source: <https://github.com/alvynmcq/diff-glance>
> Published: 2026-08-27 13:05:09+00:00

Turn messy git diffs into plain-English summaries and architecture diagrams.

```
npx diff-glance
npx diff-glance origin/main HEAD
```

Requires Node.js 18+, `git`

on `PATH`

, and an OpenAI-compatible API key (or a local Ollama endpoint). Default range is `HEAD`

vs the worktree (staged + unstaged + untracked). If the worktree is clean, that falls back to `--commit HEAD`

. The second command diffs two refs. There is no stdin pipe.

``` bash
$ diff-glance
diff-glance: analyzing diff...
diff-glance: generating summary...
diff-glance: viewer at http://127.0.0.1:53102
diff-glance: press Ctrl+C to stop
```

The local viewer (bound to `127.0.0.1`

) opens in your browser:

Use `--json`

to print the same analysis to stdout, or `-o report.html`

to write the HTML file instead of serving it.

- Line-by-line diffs do not answer “what changed and what might break.”
- A 30-second ELI5 plus a module graph is a usable mental model before a PR review.
- Lockfiles, binaries, and generated dirs are dropped before the model sees the patch.
- The viewer is an ephemeral local HTTP server. Nothing is uploaded except the truncated diff you send to the model you configured.

| Provider | How it is selected | Default model |
|---|---|---|
| OpenAI | `OPENAI_API_KEY` |
`gpt-4o-mini` |
| Google Gemini | `GEMINI_API_KEY` or `GOOGLE_API_KEY` |
`gemini-3.6-flash` |
| OpenRouter | `OPENROUTER_API_KEY` |
`openai/gpt-4o-mini` |
| Groq | `GROQ_API_KEY` |
`llama-3.3-70b-versatile` |
| Ollama | `--base-url http://127.0.0.1:11434/v1` |
`llama3.2` |
| Custom | `--base-url` + `--api-key` |
`gpt-4o-mini` unless the URL matches a row above |

Anthropic is not a native SDK path. Route it through OpenRouter (`--model anthropic/claude-sonnet-4`

) or any other OpenAI-compatible gateway. Vertex AI works the same way: pass its OpenAI-compatible `--base-url`

.

If more than one key is set, resolution order is: `--api-key`

→ `DIFF_GLANCE_API_KEY`

→ `OPENAI_API_KEY`

→ `OPENROUTER_API_KEY`

→ `GROQ_API_KEY`

→ `GEMINI_API_KEY`

/ `GOOGLE_API_KEY`

/ `GOOGLE_GENERATIVE_AI_API_KEY`

. A dummy key of `ollama`

is used only when the base URL is local and no other key is present.

| Flag | Behavior |
|---|---|
`[from]` `[to]` |
Git refs. One arg diffs that ref vs the worktree; two args diffs `from..to` . |
`-s, --staged` |
Staged changes only (`git diff --cached` ). |
`-c, --commit <sha>` |
That commit vs its parent (`<sha>^!` ). |
`-m, --model <id>` |
Model id. |
`--base-url <url>` |
OpenAI-compatible API base URL. |
`--api-key <key>` |
API key. |
`-p, --port <n>` |
Viewer port. `0` (default) picks an ephemeral port. |
`--host <host>` |
Viewer bind host. Default `127.0.0.1` . |
`--no-open` |
Do not open a browser. |
`--json` |
Print analysis JSON to stdout; skip the viewer. |
`--max-chars <n>` |
Max diff characters sent to the model. Default `80000` . |
`-o, --output <file>` |
Write HTML to a file instead of serving. |

```
diff-glance --staged
diff-glance --commit HEAD
diff-glance --json
diff-glance -o glance.html --no-open
diff-glance --base-url http://127.0.0.1:11434/v1 --model llama3.2
```

| Variable | Role |
|---|---|
`OPENAI_API_KEY` |
OpenAI key (also used as a generic key if you set a custom base URL). |
`OPENAI_BASE_URL` |
OpenAI-compatible base URL. |
`OPENAI_MODEL` |
Model id fallback. |
`DIFF_GLANCE_API_KEY` |
Overrides other keys except `--api-key` . |
`DIFF_GLANCE_BASE_URL` |
Overrides `OPENAI_BASE_URL` . |
`DIFF_GLANCE_MODEL` |
Overrides `OPENAI_MODEL` . |
`OPENROUTER_API_KEY` |
Selects OpenRouter. |
`GROQ_API_KEY` |
Selects Groq. |
`GEMINI_API_KEY` / `GOOGLE_API_KEY` / `GOOGLE_GENERATIVE_AI_API_KEY` |
Selects Gemini. |
`DIFF_GLANCE_DEBUG` |
If set, print the raw error after the one-line stderr message. |

`--base-url`

and `--model`

beat the env vars. There is no `AI_BASE_URL`

or `AI_MODEL`

.

The HTML viewer never leaves the machine. It listens on `127.0.0.1`

and serves one generated page.

Cloud providers receive the truncated unified diff (lockfiles and binaries already stripped). Point `--base-url`

at `http://127.0.0.1:11434/v1`

(Ollama or any other local OpenAI-compatible server) and the request stays on localhost — no `--local`

flag; the loopback URL is what keeps the payload off the network.

```
git clone https://github.com/alvynmcq/diff-glance.git
cd diff-glance
npm install
npm run dev
```

`npm run dev`

runs `tsx src/index.ts`

. `npm run build`

emits `dist/`

for `node bin/diff-glance.js`

. `npm run typecheck`

runs `tsc --noEmit`

.