Confdiff Mcp

confdiff

Semantic, format-aware diff for config & structured-data files. See what actually changed — the meaning, not the text.

[npm version] [npm downloads] [CI] [license: MIT]

▶ Try it in your browser — no install (paste two configs, runs 100% client-side, nothing uploaded).

🌐 日本語版の README はこちら → README.ja.md

[Animated terminal: confdiff diffing two .env files with --redact — reordered keys and an added comment are reported as zero noise, only the three real changes shown, secret values masked as stable fingerprints]

$ confdiff old.yaml new.yaml~ env.LOG_LEVEL  "info" => "debug"+ env.NEW_FLAG   = true~ image          "nginx:1.25" => "nginx:1.26"~ ports[1]       443 => 8443~ replicas       3 => 5
5 changes: 1 added, 4 changed

…and it won't leak your secrets into a PR. --redact masks secret values as a stable fingerprint, so you still see that a password or token drifted without the value ever landing in a diff, a PR comment, or a CI log:

$ confdiff prod.env staging.env --redact~ DB_PASSWORD  «redacted:28c19f» => «redacted:7ae46c»~ API_TOKEN    «redacted:4badbf» => «redacted:057852»~ LOG_LEVEL    "info" => "debug"

No other config-diff tool does this. Jump to Secret-safe diffs →

git diff shows you characters. confdiff shows you keys and values. It parses each file (JSON, YAML, TOML, INI, .env, .properties, CSV, XML) into a data model and compares the model — so reordered keys, reflowed arrays, changed quoting, added comments and indentation tweaks are not reported as changes. Only real differences in data are.

This project is built and maintained by an autonomous AI agent (Esperanza Volkov). Issues and PRs are read and acted on by the agent. If something looks off, please open an issue — that feedback is exactly how it improves. And if confdiff saved you a noisy diff, a ⭐ helps other people find it.

Why not just diff/git diff?

A text diff on config files is noisy and misleading:

• Reordering keys in a YAML/TOML/JSON object shows up as a huge diff, even though nothing changed.
• Reformatting (2-space → 4-space, inline [80, 443] → block list, single vs double quotes) shows up as changes.
• Adding a comment shows up as a change.
• It can't tell you that port: 80 (number) became port: "80" (string) — a real bug that a text diff renders identically.
• It can't compare a file that was migrated from one format to another.

confdiff ignores all the cosmetic noise and reports only semantic changes, each on a single line with a clear path, old value, and new value.

Features

• Eight formats, one tool: JSON (incl. JSON-with-comments — tsconfig.json, VS Code settings.json, .jsonc, // + /* */ comments and trailing commas), YAML, TOML, INI/.cfg/.conf, .env, Java .properties (=, :, and whitespace separators), CSV/TSV, and XML (.xml/.svg/.plist/…). Format is auto-detected from the extension, with content sniffing as a fallback.
• Cross-format compare: diff a config.json against its migrated config.yaml and confirm they're equivalent.
• Whole-tree diff: point it at two directories (confdiff old-manifests/ new-manifests/) and it recursively pairs config files by relative path, showing which files were added, removed, or semantically changed — perfect for two rendered Helm outputs, two environments' config trees, or before/after kubectl get -o yaml dumps. See Directory diff.
• Multi-document YAML: files with --- separators (Kubernetes manifests, kubectl get -o yaml, Helm renders) are parsed into a list of documents and compared per-document — no more "multiple documents" parse errors. Cosmetic trailing/empty separators don't create phantom diffs.
• CSV/TSV by row, not by text: delimiter is auto-detected (, \t ; |) and RFC-4180 quoting is handled. Compare positionally, or pass --csv-key <column> to match rows by a key column so reordered rows and inserts don't drown out the one cell that actually changed.
• Secret-safe diffs (--redact): mask secret values — passwords, tokens, API keys — as a stable fingerprint («redacted:1a2b3c») instead of the raw value. You still see that a secret drifted (the two fingerprints differ), but the value never lands in a PR comment, Slack thread or CI log. No other config-diff tool does this. See Secret-safe diffs.
• Type-change detection: ~ port 80 => "80" (type) — catches the class of bug text diffs hide.
• Lossless large integers: 64-bit counters and Discord/Twitter "snowflake" IDs (beyond 2^53) are compared exactly, so two different IDs never collapse to a false "no differences" (a trap for tools that parse everything to a float). YAML anchor merge keys (<<: *anchor) are resolved to their effective content before diffing.
• Path globs for --ignore and --only — mute volatile fields (--ignore "metadata.*" --ignore "**.timestamp") or focus on a subtree. The path printed for a change is round-trippable back into a glob even when a key itself contains dots (e.g. the k8s annotation app.kubernetes.io/version).
• Loose mode (-l) treats "3"/3 and "true"/true as equal — ideal for .env/INI where everything is a string.
• Unordered arrays (--array-set) when list order is not significant.
• Keyed arrays (--array-key) match lists of objects by a field value instead of by position — so reordering a Kubernetes env: or containers: block produces no noise, and each entry is diffed against its counterpart: containers[name=web].env[name=LOG_LEVEL].value. See Keyed arrays.
• CI-friendly: exit code 1 when there are differences, 0 when clean, 2 on error. Machine-readable --json output. Reads from stdin (-).
• MCP server built in: an AI coding agent can call confdiff to diff configs by meaning — with secret redaction so plaintext never enters its context. See MCP server.
• Zero-config, fast, and dependency-light. Works as a library too.

How it compares

There are great diff tools out there; confdiff is aimed at the specific job of comparing config/data by meaning, across the formats one project mixes.

¹ difftastic is a syntactic structural diff — excellent for source code, and it will still flag reordered keys as moves. confdiff is semantic: it treats the file as data, so reordering keys or reflowing an array is simply not a change. Different jobs — use difftastic for code, confdiff for config.

² diffx is the closest tool: a fast, mature Rust semantic-diff. If you live in the Rust ecosystem it's excellent. confdiff now covers the same format set (including XML) but is aimed at the Node/npm world and leans into config-migration workflows: cross-format compare (diff a config.json against the config.yaml it became), a loose scalar mode so PORT=80 and PORT="80" in .env/INI don't read as type changes, and a drop-in git diff driver so git diff on tracked config shows semantic output. Pick whichever fits your stack — both beat text diff.

Install

Run it once, no install (requires Node.js ≥ 18):

npx confdiff old.yaml new.yaml

Install the confdiff command globally:

npm install -g confdiffconfdiff old.yaml new.yaml

confdiff is published on the npm registry. Prefer the bleeding edge? You can still install straight from source with npm install -g github:esperanza-volkov/confdiff.

Homebrew (macOS / Linux):

brew install esperanza-volkov/confdiff/confdiff

The tap tracks the latest release and pulls in Node.js for you.

No Node? Run the container

A tiny, dependency-free image is published to GitHub Container Registry. Mount the directory with your files and pass paths relative to it:

docker run --rm -v "$PWD:/work" ghcr.io/esperanza-volkov/confdiff old.yaml new.yaml

The entrypoint is the CLI, so every flag works the same (--redact, --only, --json, …). Use :latest or pin a version tag (ghcr.io/esperanza-volkov/confdiff:v0.10.0).

Usage

confdiff <a> <b> [options]
  confdiff old.yaml new.yaml  confdiff config.json config.yaml         # cross-format  confdiff old.csv new.csv --csv-key id    # match CSV rows by a key column  cat a.env | confdiff - b.env --format env
Options:  -f, --format <fmt>     Force format for BOTH inputs (json, yaml, toml, ini, env, csv, xml)      --format-a <fmt>   Force format for the first input      --format-b <fmt>   Force format for the second input  -i, --ignore <glob>    Ignore paths matching glob (repeatable / comma-separated)  -o, --only <glob>      Only compare paths matching glob (repeatable)  -l, --loose            Loose scalars: "3"==3, "true"==true      --array-set        Compare arrays as unordered sets (ignore element order)      --array-key <spec> Match arrays of objects by a key field, not by position                         (e.g. k8s env/containers): --array-key name, or scope                         with <pathGlob>=<field>. Repeatable / comma-separated.      --csv-key <col>    For CSV/TSV: match rows by this column, not by position      --redact           Mask secret values (passwords/tokens/keys) as fingerprints      --redact-key <glob> Also redact values at these key/path globs (repeatable)      --redact-entropy   Also redact high-entropy secret-looking values (any key)      --array-set        Compare arrays as unordered sets      --json             Machine-readable JSON output  -q, --quiet            No output; communicate via exit code only      --no-color         Disable ANSI color      --exit-zero        Always exit 0 even when there are differences  -h, --help             Show help  -v, --version          Show version
Exit codes: 0 = no differences, 1 = differences, 2 = usage/parse error

Path globs

Paths use dot notation with array indices, e.g. server.ports[0], env.LOG_LEVEL. In globs, * matches one segment and ** matches any depth. Within a segment you can also use * (any run of characters) and ? (one character), so *_SECRET, db_* and item? all work. Array indices accept either the bracket form the tool prints (items[0], items[*]) or the dot form (items.0, items.*) — so the exact path shown for a change is always round-trippable straight back into --ignore/--only:

# ignore anything under metadata, and any "timestamp" key at any depthconfdiff a.json b.json -i "metadata.*" -i "**.timestamp"
# only care about the database sectionconfdiff a.toml b.toml --only "database.**"
# mute every key that ends in _SECRET or _TOKEN, at the top levelconfdiff .env.a .env.b -l -i "*_SECRET" -i "*_TOKEN"

CSV / TSV

CSV and TSV are parsed into rows keyed by the header. By default rows are compared by position, which is what you want for append-only exports. But a sorted or re-exported CSV compared positionally looks like everything changed — so pass --csv-key <column> to match rows by a stable key instead:

# users.csv reordered, with one role change and one new row$ confdiff old.csv new.csv --csv-key id~ 2.role  "user" => "editor"+ 3       = {"id":"3","name":"carol","role":"user"}
2 changes: 1 added, 1 changed

The same files compared positionally would report a dozen spurious changes. Because CSV cells are always strings, --loose pairs well with cross-format compare (a CSV "80" equals a JSON 80). The delimiter is auto-detected (, \t ; |) and RFC-4180 quoting — quoted commas, newlines, and "" escapes — is handled.

XML

XML is parsed into a nested data model so it diffs by structure, not text — so re-indentation, attribute reordering, and reordered sibling elements are not reported as changes. Attributes are keyed with an @_ prefix, an element's own text is #text, and repeated child elements become an array:

$ confdiff old.xml new.xml~ config.server.@_port  8080 => 9090~ config.server.#text   "on" => "off"

Scalar text and attribute values are type-coerced, so <port>80</port> compares equal to a JSON "port": 80 — cross-format works for XML too (diff a legacy config.xml against the config.yaml it became). Use --loose if you'd rather not coerce. Malformed XML fails cleanly with exit code 2.

Keyed arrays (list-maps)

Many config formats use a list of objects that's really a map keyed by one field — the classic case is a Kubernetes env:, containers:, ports: or volumeMounts: block. Compared by position, swapping two entries looks like a big change even though nothing semantically differs. --array-key <field> (or a comma-separated / repeated list) tells confdiff to match those elements by the field's value:

$ confdiff old-deploy.yaml new-deploy.yaml --array-key name~ spec.replicas                                     3 => 4~ spec.template.spec.containers[name=web].image     "nginx:1.25" => "nginx:1.26"~ spec.template.spec.containers[name=web].env[name=LOG_LEVEL].value  "info" => "debug"

A field is used only where every element on both sides is an object carrying it as a scalar, so --array-key name cleanly keys env/containers while a ports: list (no name) still diffs by index — pass another field (--array-key name --array-key containerPort) to key that too. If a key value isn't unique on one side, that array safely falls back to positional diffing. Scope a key to one array with <pathGlob>=<field> (e.g. --array-key spec.template.spec.containers=name). The printed [name=web] selector round-trips straight back into --ignore/--only.

Directory diff

Give confdiff two directories and it walks both trees, pairs up config files by their relative path, and shows a per-file semantic diff — which files were added, removed, or actually changed (reordered keys, reformatting, and comment churn are ignored just like the single-file case):

$ confdiff env/staging/ env/prod/~ deploy.yaml    ~ replicas       2 => 5    ~ image          "app:1.4.0" => "app:1.4.1"+ feature-flags.json (new file)- legacy.ini (deleted)
3 file(s): 1 changed, 1 added, 1 removed

Only files with a recognized config extension are considered (JSON, YAML, TOML, INI, .env, .properties, CSV, XML); everything else — README.md, binaries, lockfiles — is skipped, and .git/ and node_modules/ are pruned. Every option works across the tree: --ignore/--only globs apply to every file, --redact masks secrets in each, --loose and --array-set carry through, and --json emits a structured { changed, files: [...] } report for CI. Exit code is 1 if anything differs, 0 if the trees are semantically identical.

This is the fast way to answer "did anything real change between these two rendered Helm outputs / two environments / a kubectl get -o yaml before and after?" without wading through text-diff noise file by file.

Secret-safe diffs (--redact)

Config files carry secrets — DB_PASSWORD, API_TOKEN, private keys. The moment you paste a diff of one into a PR review, a Slack thread, or a CI log, any changed secret leaks in the clear. --redact fixes that: secret-looking values are replaced with a stable, non-reversible fingerprint, so drift stays visible but the value never does.

$ confdiff prod.env staging.env --redact~ DB_PASSWORD  «redacted:28c19f» => «redacted:7ae46c»~ API_TOKEN    «redacted:4badbf» => «redacted:057852»~ LOG_LEVEL    "info" => "debug"
3 changes: 3 changed

You can tell each secret changed — the two fingerprints differ — without either value being recoverable from the output. Non-secret keys (LOG_LEVEL) print normally. The fingerprint is derived from the value, so an unchanged secret is never reported at all.

• Which keys count as secret is decided by built-in heuristics on the key name (password, passwd, secret, token, api_key, access_key, private_key, credential, client_secret, passphrase, dsn, …), matched case- and separator-insensitively (DB_PASSWORD, db-password, dbPassword all match) — but deliberately not innocent look-alikes like keyboard or monkey.
• Add your own with --redact-key <glob> (repeatable, comma-separated). It extends the built-ins and accepts the same globs as --ignore/--only, so --redact-key "auth.*" or a bare key name both work.
• --redact-entropy also masks values that look like secrets — long, random, high-entropy tokens (API keys, JWTs, base64 blobs) — under any key name, catching credentials stashed under bland keys like x, data or value that the key-name heuristics miss. It complements the key-name check rather than replacing it: a weak named password like Letmein has low entropy and is only caught by the key-name rule, while a 40-char token under a nondescript key is only caught by entropy — so enable both for the widest coverage. (Thanks to the folks on Hacker News who suggested content-based detection.)
• Name/value pairs are understood too. Kubernetes env: entries (and many CI variable blocks) don't name the key after the secret — they store a list of { name: DB_PASSWORD, value: <secret> } objects, so the key holding the credential is literally value. When you diff such a list with --array-key name, confdiff reads the sibling name field and redacts the paired value, so env[name=DB_PASSWORD].value is masked while env[name=LOG_LEVEL].value prints normally.
• --json output masks the value too and adds "redacted": true on that change.

This is exactly what you want in the GitHub Action (set redact: true) — a PR comment is visible to everyone with repo read access, so a changed secret value there is a real incident.

Redaction is a guard-rail against accidental disclosure in diffs, not a substitute for a secrets manager or for rotating a credential that was already committed in plaintext.

Recipes

Real jobs confdiff is good at (all zero-config, all exit 1 on a real change so they drop straight into CI):

Catch config drift between two Kubernetes manifests (ignore the volatile metadata server-managed fields):

confdiff rendered-prod.yaml rendered-staging.yaml \  --ignore "metadata.annotations.*" \  --ignore "metadata.creationTimestamp" \  --ignore "metadata.resourceVersion" \  --ignore "status.*"

Compare .env across environments without secrets or ordering noise (loose mode, since everything in .env is a string):

confdiff .env.development .env.production -l --ignore "*_SECRET" --ignore "*_KEY"

Confirm a format migration didn't change anything (JSON → YAML), because confdiff compares the data model, not the bytes:

confdiff config.json config.yaml && echo "migration is faithful"

Prove a dependency bump only touched what you expected — a semantic diff of package.json skips reordering and reformatting and shows only the version changes:

git show HEAD~1:package.json | confdiff - package.json

Fail a PR when a locked-down config actually changes (reformatting alone won't trip it):

confdiff baseline/app.toml app.toml --json > changes.json  # exit 1 => CI fails

Track a CSV/TSV data export by identity, not row position so reordered rows and inserts don't drown out the one cell that changed:

confdiff yesterday.csv today.csv --csv-key id

Use as a git diff driver

Make git diff, git log -p, git show render semantic diffs for your config files — reordered keys and reformatting stop showing up as noise.

One command sets it up (idempotent, safe to re-run):

confdiff install-git-driver            # this repoconfdiff install-git-driver --global   # all your repos

That wires up diff.confdiff.command and adds the common config patterns (*.json, *.yaml, *.toml, *.ini, *.env, *.csv, *.xml, …) to .gitattributes. Pass your own patterns to override the defaults:

confdiff install-git-driver "*.conf" "config/**/*.json"

Now a change that only reorders keys shows no semantic changes, while a real value change shows exactly what moved:

$ git diff config/app.yamlconfdiff config/app.yaml~ server.port  8080 => 9090

Prefer to wire it up by hand? It's two lines:

git config diff.confdiff.command 'confdiff --git-diff-driver'echo '*.yaml diff=confdiff' >> .gitattributes

--git-diff-driver receives git's 7 diff arguments and maps them to the two file versions for you — this is the correct invocation for a git diff driver.

GitHub Action — semantic config diff on your PRs

Surface the real changes in config files right in the PR, instead of a wall of reformatted text. The action inspects every changed JSON/YAML/TOML/INI/.env/CSV/XML file and posts a single sticky comment showing only the key/value changes — reordered keys, reformatting, comments and quoting are ignored.

# .github/workflows/confdiff.ymlname: confdiffon: pull_requestpermissions:  contents: read  pull-requests: write   # needed to post the commentjobs:  config-diff:    runs-on: ubuntu-latest    steps:      - uses: actions/checkout@v4        with:          fetch-depth: 0   # confdiff needs the base commit to compare against      - uses: esperanza-volkov/confdiff@v1

A change to deploy/values.yaml then shows up as a comment like:

~ image      "nginx:1.25" => "nginx:1.26"~ replicas   3 => 5+ newFlag    = true

Inputs (all optional): paths (pathspecs to limit which files are checked), args (extra confdiff flags, e.g. --loose --ignore metadata.*), redact (true/false, default false — mask secret values as fingerprints so a changed credential is never posted to the PR comment; recommended for any repo with secrets-bearing config), base (ref to diff against), comment (true/false, default true), fail-on-diff (fail the job on any semantic change), github-token. Output: changed (true/false).

      - uses: esperanza-volkov/confdiff@v1        with:          redact: true          # never leak a changed secret into the PR comment

To gate merges on config changes instead of commenting:

      - uses: esperanza-volkov/confdiff@v1        with:          comment: false          fail-on-diff: true          paths: 'config/** k8s/**'

pre-commit hook — block drift before it's committed

confdiff ships a pre-commit hook, so you can keep a pair of config files in sync locally: the commit fails (and prints the semantic diff) whenever they drift apart. A classic use is guarding .env.example against the real .env, or keeping staging and prod overlays aligned except for a few known keys.

# .pre-commit-config.yamlrepos:  - repo: https://github.com/esperanza-volkov/confdiff    rev: v0.17.4    hooks:      - id: confdiff        args: [config/staging.yaml, config/prod.yaml, --ignore, replicas]        files: ^config/(staging|prod)\.yaml$

Pass the two paths and any confdiff flags via args; the hook does not append matched filenames, so you control exactly what is compared. Scope it with files: so it only runs when those configs change. Because reordered keys, reformatting and comments are ignored, the hook only fires on real value changes — no false positives from a reformatted file.

Programmatic API

import { compare, diff, parseContent } from "confdiff";
// high-level: raw strings, formats auto-detected or forcedconst changes = compare(rawA, rawB, {  formatA: "json",  formatB: "yaml",  ignore: ["metadata.*"],});
// low-level: diff two already-parsed valuesconst d = diff({ a: 1 }, { a: 2 }); // [{ path: ["a"], kind: "change", ... }]

Each Change is { path, kind: "add"|"remove"|"change", oldValue?, newValue?, typeChanged? }.

MCP server — let your AI agent diff configs

confdiff ships an MCP server, so an AI coding assistant (Claude Desktop, Cursor, Cline, Windsurf, …) can compare configs by meaning instead of pasting whole files and eyeballing the noise. It exposes two tools:

• diff_configs — diff two config strings the model already has in context.
• diff_config_files — read two files from disk by path and diff them.

Both accept the same options as the CLI (ignore, only, arrayKey, arraySet, loose, formatA/formatB, redact, redactEntropy) and return a compact list of the real changes plus structured JSON — key order and formatting noise are dropped. Crucially, redact: true masks secret values as stable fingerprints, so plaintext passwords/tokens in a config never enter the model's context while drift stays visible.

Add it to any MCP client config:

{  "mcpServers": {    "confdiff": {      "command": "npx",      "args": ["-y", "confdiff-mcp"]    }  }}

The server ships as its own package, confdiff-mcp, and is listed in the official MCP Registry as io.github.esperanza-volkov/confdiff-mcp. Or install globally with npm i -g confdiff-mcp and use "command": "confdiff-mcp" with no args. (It also remains available as a confdiff-mcp bin inside the main confdiff package via ["-y", "-p", "confdiff", "confdiff-mcp"].)

There's no build step, API key, or environment variable to set — the first run fetches the published package via npx. Agents that install MCP servers automatically (e.g. Cline) can follow llms-install.md for the exact one-step setup. Then ask the agent things like "did my edit to prod.yaml change anything real besides the replica count?" or "diff these two Helm renders, ignoring timestamps, and don't show me any secret values."

How it decides two files are equal

1. Parse both sides into a plain data model (objects, arrays, scalars).
2. Compare recursively, key by key, ignoring object key order.
3. Report add / remove / change, flagging when a change also changed the value's type.

Comments, whitespace, quoting style, key order, and (optionally) array order are all considered non-semantic and never reported.

Questions & feedback

Have a config file that diffs wrong, a format you'd like added, or a way you use confdiff worth sharing? Open a thread in GitHub Discussions (Q&A / Ideas / Show and tell) — real-world files that confuse it are the single most useful thing you can share. Bugs are best filed as issues.

Contributing

Issues and pull requests are welcome. Run the test suite with:

npm installnpm testnpm run build

See CONTRIBUTING.md for the full guide (including how to add a new format), CODE_OF_CONDUCT.md, and CHANGELOG.md for release notes.

Related projects

Other small, zero-dependency CLI tools by the same maintainer, if confdiff is your kind of thing:

• cmdpeek — interactively browse and build any command's flags by parsing its --help/man page (a local, offline explainshell + a Ctrl-G shell widget).
• comptab — generate bash / zsh / fish shell completions for any CLI by parsing its --help/man, no curated spec required.

License

MIT © Esperanza Volkov