smart-diff

Generate AI-powered natural-language summaries of git diffs for code review in any git repository.

Supports OpenAI, Anthropic, Google Gemini, Amazon Bedrock, Mistral, Cohere, Groq, xAI, DeepSeek, or any OpenAI-compatible gateway.

• Requirements
• Installation
• Provider configuration
• Usage
  • Use as a Library - summarizeGitDiff
  • Use as a CLI
  • Options reference
  • Handling large diffs
  • Token usage reporting
  • Injecting your own ChatModel
  • Diff shape: single range vs per-commit
  • Lower-level API
• GitHub Action
• Used By
• License

Requirements

• Node.js 22.22.1+
• An LLM provider credential (see Provider configuration)
• No git binary required, on any platform — smart-diff reads the git repository directly via @scolladon/tsgit, a pure-TypeScript git implementation with zero native dependencies

Installation

npm install @mcarvin/smart-diff

Provider configuration

smart-diff is "configured" when isLlmProviderConfigured() returns true — i.e. at least one supported provider can be resolved from env vars — or you pass your own llmModelProvider factory. Otherwise summarizeGitDiff / generateSummary throw with LLM_GATEWAY_REQUIRED_MESSAGE.

Selecting a provider

LLM_PROVIDER explicitly selects a provider. When unset, the resolver auto-detects in this order: LLM_BASE_URL/OPENAI_BASE_URL → openai-compatible, OPENAI_API_KEY/LLM_API_KEY → openai, then ANTHROPIC_API_KEY, GOOGLE_GENERATIVE_AI_API_KEY (or GOOGLE_API_KEY), MISTRAL_API_KEY, COHERE_API_KEY, GROQ_API_KEY, XAI_API_KEY, DEEPSEEK_API_KEY, AWS_ACCESS_KEY_ID/AWS_PROFILE → bedrock, and finally OPENAI_DEFAULT_HEADERS/LLM_DEFAULT_HEADERS → openai.

| Provider (LLM_PROVIDER) | Endpoint | Credential env vars | Default model | |---|---|---|---| | openai | OpenAI Chat Completions | OPENAI_API_KEY or LLM_API_KEY | gpt-4o-mini | | openai-compatible | Chat Completions at LLM_BASE_URL/OPENAI_BASE_URL | LLM_BASE_URL or OPENAI_BASE_URL (required); OPENAI_API_KEY/LLM_API_KEY or custom headers | gpt-4o-mini | | anthropic | Anthropic Messages API | ANTHROPIC_API_KEY | claude-haiku-4-5-20251001 | | google | Gemini Generative Language API | GOOGLE_GENERATIVE_AI_API_KEY or GOOGLE_API_KEY | gemini-2.0-flash | | bedrock | Bedrock Converse API (in-house SigV4 signing) | AWS_ACCESS_KEY_ID+AWS_SECRET_ACCESS_KEY (+ optional AWS_SESSION_TOKEN), or AWS_PROFILE pointing at a profile in ~/.aws/credentials; region from AWS_REGION/AWS_DEFAULT_REGION/~/.aws/config (default us-east-1). SSO, instance-role, and container credentials are not supported — static credentials only. | anthropic.claude-3-5-haiku-20241022-v1:0 | | mistral | Mistral Chat Completions API | MISTRAL_API_KEY | mistral-small-latest | | cohere | Cohere Chat API (v2) | COHERE_API_KEY | command-r-08-2024 | | groq | Groq Chat Completions API | GROQ_API_KEY | llama-3.1-8b-instant | | xai | xAI Chat Completions API | XAI_API_KEY | grok-2-latest | | deepseek | DeepSeek Chat Completions API | DEEPSEEK_API_KEY | deepseek-chat |

LLM_* wins over OPENAI_* where both exist.

Common env vars

| Variable | Purpose | |---|---| | LLM_PROVIDER | Explicit provider id from the table above. | | LLM_MODEL | Overrides the per-provider default model id. | | OPENAI_BASE_URL / LLM_BASE_URL | Base URL for an OpenAI-compatible gateway; presence alone auto-selects the openai-compatible provider. | | OPENAI_DEFAULT_HEADERS / LLM_DEFAULT_HEADERS | JSON object of extra headers merged onto OpenAI / OpenAI-compatible requests (e.g. RBAC tokens, raw Authorization). LLM_* overrides OPENAI_* key-by-key. | | LLM_PROVIDER_NAME | Display name used when openai-compatible is active (defaults to openai-compatible). | | OPENAI_MAX_DIFF_CHARS / LLM_MAX_DIFF_CHARS | Max size of unified diff text sent to the model (default ~120k characters). | | OPENAI_MAX_TOKENS / LLM_MAX_TOKENS | Max completion tokens (default 4000). | | LLM_TEMPERATURE | Sampling temperature, clamped to 0–2 (default 0.2). Lower = more deterministic; higher = more varied prose. | | LLM_MAX_RETRIES | Retry count for transient LLM call failures — rate limits, 5xx, network errors (default 2). Set to 0 to disable retries. |

Example: native OpenAI

$env:OPENAI_API_KEY = "sk-..."
# Optional: $env:LLM_MODEL = "gpt-4o"

Example: Anthropic Claude

$env:ANTHROPIC_API_KEY = "sk-ant-..."
$env:LLM_MODEL = "claude-3-5-sonnet-latest"   # optional override

Example: company-managed OpenAI-compatible gateway

$env:OPENAI_BASE_URL = "https://llm-gateway.example.com"
$env:OPENAI_DEFAULT_HEADERS = '{"x-company-rbac":"your-rbac-token-here","Authorization":"Bearer sk-your-api-key-here"}'
# LLM_PROVIDER is auto-detected as "openai-compatible" because LLM_BASE_URL/OPENAI_BASE_URL is set.

Example: Google Gemini

$env:GOOGLE_GENERATIVE_AI_API_KEY = "..."
$env:LLM_MODEL = "gemini-2.0-flash"

Usage

Use smart-diff as a library, or as the smart-diff CLI binary that ships with the package via the bin field — no separate install. Provider configuration is identical either way; see Provider configuration. Every option below has a library form (a key in the summarizeGitDiff object) and, where applicable, an equivalent kebab-case CLI flag.

Use as a Library - summarizeGitDiff

import { summarizeGitDiff } from '@mcarvin/smart-diff';

const { summary, usage } = await summarizeGitDiff({
  from: 'origin/main',
  to: 'HEAD',
  cwd: '/path/to/repo', // optional; default process.cwd()
  includeFolders: ['src'],
  excludeFolders: ['node_modules', 'dist'],
  commitMessageExcludeRegexes: ['^\\[bot\\]'],
  commitMessageIncludeRegexes: ['^feat:'], // optional; OR across patterns
  teamName: 'Platform',
  systemPrompt: undefined,   // optional; overrides DEFAULT_GIT_DIFF_SYSTEM_PROMPT
  provider: 'anthropic',     // optional; overrides LLM_PROVIDER env + auto-detection
  model: 'claude-3-5-sonnet-latest', // optional
  maxDiffChars: 120_000,     // optional; also see LLM_MAX_DIFF_CHARS
});
// summary: Markdown string
// usage: LlmUsageReport aggregated across every LLM call — see Token usage reporting below

Use as a CLI

npm install @mcarvin/smart-diff
npx smart-diff origin/main HEAD --team Platform --max-diff-chars 20000
npx smart-diff --help

• <from> (required) and [to] (default HEAD) can be passed positionally or via --from/--to.
• Pass --merge-base / -b alongside <from>/--from to resolve it as the merge base of to and from instead of using it directly — e.g. --to develop --from main --merge-base is the tsgit-native equivalent of --to develop --from $(git merge-base develop main), with no local git binary required.
• Repeatable options (--include, --exclude, --commit-include, --commit-exclude) accept multiple flags.
• The Markdown summary is printed to stdout; errors go to stderr and exit with code 1.
• Run smart-diff --help for the full flag reference, or smart-diff --version for the installed version.

Options reference

Core

| Option | CLI flag | Description | |--------|----------|-------------| | from / to | <from> [to] / --from / --to | Git refs for the range; to defaults to HEAD. | | mergeBase | --merge-base, -b | Resolve from as the merge base of to and from, in-process via tsgit — no local git binary needed. | | cwd / git | --cwd <path> | Working directory path, or inject your own GitClient instance (library only; see Lower-level API). | | includeFolders | --include <path> | Limit diff to these paths relative to repo root (omit for full repo minus excludes). | | excludeFolders | --exclude <path> | Excluded paths, applied client-side to the changed-path list (directory-prefix match), e.g. node_modules. | | commitMessageIncludeRegexes | --commit-include <regex> | If any pattern is non-empty, only commits whose full message matches at least one pattern are kept (after excludes). Case-insensitive. | | commitMessageExcludeRegexes | --commit-exclude <regex> | Drop commits whose message matches any of these patterns. | | teamName | --team <name> | Adds a Team: line to the user payload for the model. | | systemPrompt | --system-prompt <text> | Replaces the default system prompt. | | provider | --provider <id> | LlmProviderId — wins over LLM_PROVIDER env and auto-detection. | | model | --model <id> | Chat model id; overrides LLM_MODEL and the provider default. | | llmModelProvider | — (library only) | () => Promise<ChatModel> — bypass env-based resolution entirely; hand-wire your own ChatModel (required in tests or custom setups). |

Token reduction — see Handling large diffs

| Option | CLI flag | Description | |--------|----------|-------------| | maxDiffChars | --max-diff-chars <n> | Caps unified diff size for the request; see LLM_MAX_DIFF_CHARS. | | mapReduce | --map-reduce | Split an oversized diff into per-file batches instead of hard-truncating it. | | contextLines | --context-lines <n> | Number of context lines around each change (git diff -U<n>). Lower values (1 or 0) are the single biggest token saver on modification-heavy diffs. | | ignoreWhitespace | --ignore-whitespace | Passes -w / --ignore-all-space to git diff so pure-whitespace hunks don't consume tokens. Also applies to --numstat / --name-status so counts stay consistent. | | stripDiffPreamble | --strip-diff-preamble | Removes low-value lines from the unified diff (diff --git, index, mode changes, similarity/rename/copy metadata). --- a/…, +++ b/…, and @@ hunk headers are kept. | | maxHunkLines | --max-hunk-lines <n> | Caps the body of each hunk; anything past the limit is replaced with a single elision marker. The @@ header and DiffSummary totals are preserved. | | excludeDefaultNoise | --exclude-default-noise | Merges the built-in DEFAULT_NOISE_EXCLUDES list (lockfiles, dist, build, out, coverage, node_modules, __snapshots__) into excludeFolders. |

Reliability

| Option | CLI flag | Description | |--------|----------|-------------| | maxRetries | --max-retries <n> | Retry count for transient LLM call failures; see LLM_MAX_RETRIES. |

Security

| Option | CLI flag | Description | |--------|----------|-------------| | redactSecrets | --redact-secrets | Masks likely secrets/credentials in the diff text before it's sent to the LLM — cloud provider keys, VCS/chat tokens, PEM private key blocks, JWTs, Bearer headers, basic-auth URL passwords, and generic KEY=value assignments. Uses DEFAULT_SECRET_PATTERNS unless secretPatterns overrides them. | | secretPatterns | — (library only) | Overrides the built-in secret-detection rules used when redactSecrets is true. |

Other

| Option | CLI flag | Description | |--------|----------|-------------| | — (summarizeGitDiff always returns usage) | --usage | Print the same LlmUsageReport as Token usage reporting to stderr, after the Markdown summary on stdout. | | — | -h, --help | Show CLI help. | | — | -v, --version | Print the installed version. |

Handling large diffs

Reducing tokens

For most repos, the cheapest wins are:

await summarizeGitDiff({
  from: 'origin/main',
  contextLines: 1,          // -U1 cuts 30-60% of tokens on typical diffs
  ignoreWhitespace: true,   // drop pure-whitespace hunks entirely
  stripDiffPreamble: true,  // kill `index`/`mode`/`similarity` lines
  maxHunkLines: 400,        // truncate monster hunks but keep the @@ header
  excludeDefaultNoise: true // skip lockfiles, dist/, coverage/, node_modules/
});

These options only reshape the unified diff text — the structured DiffSummary still reports true file counts and line totals, so the model always sees the full change inventory.

Map-reduce for oversized diffs

By default, a diff over maxDiffChars is hard-truncated — only the first N characters are sent, and a notice is prepended to the summary. Set mapReduce: true to instead split the diff into per-file batches, summarize each batch independently, then synthesize one final summary from the batch summaries:

await summarizeGitDiff({
  from: 'origin/main',
  maxDiffChars: 20_000,
  mapReduce: true, // no-op when the diff already fits within maxDiffChars
});

This costs one extra LLM call per batch plus one reduce call, so it's slower and more expensive than a single request — use it when losing coverage of the tail of a large diff matters more than latency/cost. systemPrompt (if set) applies to the reduce phase only; the map phase always uses DEFAULT_MAP_REDUCE_MAP_SYSTEM_PROMPT.

Token usage reporting

summarizeGitDiff returns the Markdown summary plus token usage aggregated across every LLM call made to produce it — one call by default, or every map-reduce batch plus the reduce call when mapReduce is used:

import { summarizeGitDiff } from '@mcarvin/smart-diff';

const { summary, usage } = await summarizeGitDiff({ from: 'origin/main' });
// usage: { requestCount, inputTokens, outputTokens, totalTokens, cachedInputTokens }

This reports token counts only — no dollar cost estimate, since per-token pricing varies by provider/model and changes over time; a hardcoded price table would drift out of date. Fields are 0 when a provider doesn't report a given figure. generateSummaryWithUsage is the lower-level equivalent of generateSummary.

Injecting your own ChatModel

If you want full control — for example, to hit an in-process mock, add your own middleware/logging, or talk to a provider smart-diff doesn't support directly — pass llmModelProvider. A ChatModel is just an object with a generate method:

import { summarizeGitDiff, type ChatModel } from '@mcarvin/smart-diff';

const myModel: ChatModel = {
  async generate({ system, prompt, temperature, maxOutputTokens }) {
    const res = await fetch('https://my-llm-gateway.example.com/v1/chat', {
      method: 'POST',
      headers: { authorization: `Bearer ${process.env.MY_GATEWAY_KEY}` },
      body: JSON.stringify({ system, prompt, temperature, maxOutputTokens }),
    });
    const data = await res.json();
    return { text: data.text, usage: { inputTokens: data.inputTokens, outputTokens: data.outputTokens } };
  },
};

const { summary } = await summarizeGitDiff({
  from: 'origin/main',
  llmModelProvider: async () => myModel,
});

Diff shape: single range vs per-commit

• Single unified diff for from..to when no commit-message filters apply and the filtered commit list matches the full log for that range.
• Concatenated per-commit patches (each commit diffed against its first parent, or the empty tree for a root commit) when you use include/exclude regexes or when the filtered commit list differs in length from the full range (so the diff reflects only the commits that remain).

Lower-level API

The package also exports helpers for building a custom pipeline on top of the same git and LLM behavior:

• Git: createGitClient(cwd?, timeout?) (async — returns Promise<GitClient>, a live @scolladon/tsgit repository handle; call git.dispose() when done), getRepoRoot, getCommits, getDiff, getDiffSummary, getChangedFiles, filterCommitsByMessageRegexes, buildPathFilterPredicate, matchesAnyPath, renderFileDiff, renderUnifiedDiff, buildFileSummary, mergeFileSummariesByPath, summarizeFiles, shapeUnifiedDiff, redactSecrets, DEFAULT_NOISE_EXCLUDES, DEFAULT_SECRET_PATTERNS — timeout is in milliseconds; omit for no timeout
• AI: generateSummary, generateSummaryWithUsage, resolveLlmMaxDiffChars, resolveLlmMaxRetries, truncateUnifiedDiffForLlm, splitUnifiedDiffIntoFileChunks, groupDiffChunksByBudget
• Provider resolution: resolveLanguageModel, detectLlmProvider, isLlmProviderConfigured, defaultModelForProvider, resolveLlmBaseUrl, parseLlmDefaultHeadersFromEnv
• Constants: DEFAULT_GIT_DIFF_SYSTEM_PROMPT, DEFAULT_MAP_REDUCE_MAP_SYSTEM_PROMPT, DEFAULT_MAP_REDUCE_REDUCE_SYSTEM_PROMPT, LLM_GATEWAY_REQUIRED_MESSAGE
• Types: LlmProviderId, LlmModelProvider, ChatModel, ChatCallOptions, ChatResult, ChatUsage, ResolveLanguageModelOptions, GenerateSummaryInput, SummarizeFlags, LlmUsageReport, DiffFileSummary, DiffSummary, CommitInfo, GitClient, GitDiffRangeQuery, DiffPathFilter, DiffShapingOptions, PathFilterPredicate, RenderedFileDiff, SecretRedactionRule
  • DiffFileSummary.binary?: boolean is true when either blob sniffs as binary; absent for text files

GitHub Action

smart-diff is also published as a GitHub Action (marketplace name smart-diff-ai) — no git binary or Node install needed on the runner, since it runs on node24 from a pre-bundled executable.

- uses: actions/checkout@v7
  with:
    fetch-depth: 0 # full history so `from`/`to` refs resolve

- name: Summarize diff
  id: smart-diff
  uses: mcarvin8/smart-diff@v6
  with:
    from: ${{ github.event.pull_request.base.sha }}
    to: ${{ github.event.pull_request.head.sha }}
  env:
    ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}

- name: Comment summary on PR
  uses: peter-evans/create-or-update-comment@v5
  with:
    issue-number: ${{ github.event.pull_request.number }}
    body: ${{ steps.smart-diff.outputs.summary }}

Provider credentials are read from the environment exactly as they are for the CLI — set the relevant secret(s) (ANTHROPIC_API_KEY, OPENAI_API_KEY, etc.; see Provider configuration) via the step's env: block. Set provider explicitly if more than one provider's credentials are present in the environment.

Inputs

| Input | Description | Default | | --- | --- | --- | | from | Start ref (older side of the range). Required. | | | to | End ref. | HEAD | | merge-base | Resolve from as the merge base of to and from. | false | | working-directory | Working directory of the git repository. | runner checkout dir | | include | Only include these paths (newline-separated). | | | exclude | Exclude these paths (newline-separated). | | | commit-include | Only keep commits matching these regexes (newline-separated, OR). | | | commit-exclude | Drop commits matching these regexes (newline-separated). | | | team | Team label added to the LLM prompt. | | | system-prompt | Overrides the default system prompt. | | | provider | LLM provider id. | auto-detected | | model | Model id override. | provider default | | max-diff-chars | Caps unified diff size sent to the model. | | | max-retries | Retry count for transient LLM call failures. | 2 | | map-reduce | Batch an oversized diff instead of hard-truncating it. | false | | context-lines | Context lines per hunk (git diff -U<n>). | 3 | | ignore-whitespace | Drop pure-whitespace hunks. | false | | strip-diff-preamble | Strip diff --git/index/mode noise lines. | false | | max-hunk-lines | Elide hunk bodies longer than this many lines. | | | exclude-default-noise | Skip lockfiles/dist/build/coverage/node_modules. | false | | redact-secrets | Mask likely secrets/credentials before sending the diff to the LLM. | false |

Outputs

| Output | Description | | --- | --- | | summary | Markdown summary of the diff. | | request-count | Number of LLM calls made to produce the summary. | | input-tokens | Sum of input (prompt) tokens across all calls. | | output-tokens | Sum of output (completion) tokens across all calls. | | total-tokens | Sum of total tokens across all calls, as reported by the provider. | | cached-input-tokens | Sum of cached input tokens read across all calls (0 if unsupported/unreported). |

Used By

This package is used downstream by:

• sf-git-ai-meta-insights — Salesforce metadata wrapper compatible with Salesforce DX projects
• gitlab-llm-kit — TypeScript toolkit for GitLab REST API access and LLM-powered insights (merge requests, issues, pipelines, security, releases, wiki, and more)

License

MIT