Composable diff analysis and automation for GitHub and the CLI
Measure changes. Match rules. Act on the result.
Git gives you a patch and a pair of raw counters. diffdevil turns the details inside that diff into facts you can see in GitHub, query locally, evaluate in workflows, and hand to agents.
The CLI, library and Actions are released. The browser extension is coming to the Chrome Web Store. The GitHub App is in private preview; public access is coming.
@@ -41,2 +41,3 @@
− var limit = ReadLimit(config);
− return Clamp(value, 0, limit);
+ var limit = ReadLimit(options);
+ Guard.NonNegative(limit);
+ return Clamp(value, minimum, limit);
Replacement-aware · what a size policy counts
3changed= exact
~ 2 modified · + 1 added-only · − 0 deleted-only
Raw counters · what the patch shows
+3−2
raw churn 5 · still reported, never renamed
Calling this "5 changed lines" would misrepresent the edit. Two lines were replaced, one was added.
One workflow file gives a repository size labels, no comments, and an inspectable summary. The same engine answers local queries, script conditions, the TypeScript API and agents.
name: Pull-request size
on:
pull_request_target:
types: [opened, reopened, synchronize, edited]
permissions:
pull-requests: write
jobs:
size:
runs-on: ubuntu-latest
steps:
- uses: Wolfsblvt/diffdevil@v1See replacement-aware Changed, per-file decomposition, personal or repository size bands, and inspectable reports directly on pull requests. No workflow, App installation, or repository write access required.
Install the GitHub App once for automatic analysis, native checks, labels and managed configuration, then read pull-request flow, size and history across your repositories. No workflow file, token assembly, or runner upkeep.
Raw churn counts additions and deletions separately. Replacement-aware changed lines classify adjacent replacements once, while keeping added-only, deleted-only and modified as separate facts. Your size policy reads one number; the rest stays visible so nobody has to trust it blind.
Policy-focus metric · review
178changed
= exact
band m → size/M
Decomposition
Raw · contrast
▣ package-lock.json excluded by **/package-lock.json — observed churn would be 1,193.
diffdevil for GitHub adds replacement-aware totals, per-file decomposition, size bands and inspectable reports directly to pull requests, without requiring a repository workflow or write access.
#app · diffdevil GitHub App
Every pull request in every repository you choose, remembered: what merged, how big it was, how long it took, and how this period compares with the last. Native checks and size labels run on every pull request with the same engine and .diffdevil.yml as the Action, and nothing to maintain.
Free, Pro and Business plans. The Community App is open source (AGPL-3.0-only) and self-hostable.
Analyze once. Read the result as prose, a value, a condition, a path list, or data. False, unknown and error are different exit codes, so a shell can tell them apart.
$ diffdevil query --expr metrics.review --format value
178
$ diffdevil query --files --select path --format lines
src/Foo.cs
tests/Foo.Tests.cs
$ diffdevil check --metric changed --gt 100 && echo over
over
$ diffdevil check --metric changed --gt 1000; echo $?
1 # false, not an error
$ diffdevil analyze --format json | jq -c .totals.lines.changed
{"status":"exact","value":178}
$ diffdevil query --files --metric changed --gt 100 --select path
src/Foo.cs
$ diffdevil analyze --format agent
diffdevil.agent-report/1 schema=1.0
semantics language=diffdevil-expr/1 numbers=diffdevil-number/1 replacement_lines=replacement-lines-v1 paths=diffdevil-glob/1 presets=[] limits="diffdevil-limits/1"
source kind=git comparison=direct id="fixture-exact-comparison" base="fixture-base" head="fixture-head"
identity report="report-e0a41e5620b9af3dc270f7e1067413fc0de876c53665565916c6d4aef9d29a55" policy="policy-3254961b05ecd7c46d4f2dc17ec26d8afba67d241b462ebc1ca59116e307d4cf"
evidence status=exact file_set=complete
lines changed=178 modified=115 added_only=45 deleted_only=18
raw churn=293 added=160 deleted=133
files total=3 excluded=1 included=2 added=0 deleted=0 modified=2 renamed=0 copied=0 binary=0 unmeasurable=0
scope id="production" file_set=complete files=1 changed=173 raw_churn=286
scope id="tests" file_set=complete files=1 changed=5 raw_churn=7
metrics "churn"=293 "destructive"=133 "productionReview"=173 "review"=178 "weighted"=524
bands "size"=resolved("m",lower=100,upper=500)
…
same report → human · scalar · lines · NUL · JSON · JSONL · env · Markdown · agentstdout is the result; diagnostics go to stderr
Facts are not effects. Planning is not applying. A token being present never turns reading into writing. You declare the policy; diffdevil evaluates it, shows the intended effects, and mutates only when told to.
bands:
size:
value: metrics.review
ranges:
- { id: xs, lt: 20 }
- { id: s, lt: 100 }
- { id: m, lt: 500 }
- { id: l, lt: 1000 }
- { id: xl, otherwise: true }
rules:
size:
band: size
effects:
labels:
group: size
byBand: { xs: size/XS, s: size/S,
m: size/M, l: size/L,
xl: size/XL }{ "kind": "diffdevil.plan",
"stage": "desired",
"rules": { "size": {
"band": { "id": "m",
"lower": 100, "upper": 500 },
"disposition": "matched" } },
"operations": [
{ "kind": "label.remove",
"name": "review/destructive" },
{ "kind": "label.select",
"group": "size",
"selected": "size/M",
"members": ["size/XS", "size/S",
"size/M", "size/L",
"size/XL", "size/Unknown"] }
] }Read current labels on PR #123.
Group size: size/S present, size/M absent.
− remove size/S
+ add size/M
Unrelated labels untouched (3).
Applied 2 label changes.
Readback confirms size/M.
What an explicit apply reports. Readback is observed provider state, never assumed.
A coding agent that reads a diff re-derives arithmetic and invents precision. diffdevil hands it deterministic facts with evidence standing, in a projection built for a context window. Same semantics as the report, nothing added.
diffdevil analysis
git · fixture-base..fixture-head · direct · = exact
Changed 178 lines
+45 added only · -18 deleted only · ~115 modified
Raw +160 additions · -133 deletions · 293 churn
Files 3 total · 2 included · 1 excluded
Policy
Band size → m
Metrics churn 293 · destructive 133 · productionReview 173 · … 2 morediffdevil.agent-report/1 schema=1.0
semantics language=diffdevil-expr/1 numbers=diffdevil-number/1 replacement_lines=replacement-lines-v1 paths=diffdevil-glob/1 presets=[] limits="diffdevil-limits/1"
source kind=git comparison=direct id="fixture-exact-comparison" base="fixture-base" head="fixture-head"
identity report="report-e0a41e5620b9af3dc270f7e1067413fc0de876c53665565916c6d4aef9d29a55" policy="policy-3254961b05ecd7c46d4f2dc17ec26d8afba67d241b462ebc1ca59116e307d4cf"
evidence status=exact file_set=complete
lines changed=178 modified=115 added_only=45 deleted_only=18
raw churn=293 added=160 deleted=133
files total=3 excluded=1 included=2 added=0 deleted=0 modified=2 renamed=0 copied=0 binary=0 unmeasurable=0
scope id="production" file_set=complete files=1 changed=173 raw_churn=286
scope id="tests" file_set=complete files=1 changed=5 raw_churn=7
metrics "churn"=293 "destructive"=133 "productionReview"=173 "review"=178 "weighted"=524
bands "size"=resolved("m",lower=100,upper=500)= ≈ ? ∅ survive into this form. No judgment, no prose, no renamed churn.
A versioned Skill folder, including its core, references and notice, installed without rewriting it for your harness. It teaches the agent to analyze, query, check, plan, and apply under your explicit grant; to read = ≈ ? ∅; and to keep facts, policy, proposed and applied effects apart. It can check whether its installed version is current.
---
name: diffdevil
description: >-
Use proactively during code review, PR preparation, change summaries, local
checks, and CI or policy work whenever measured changes or file selections
would help. Prefer diffdevil to hand-counting diffs or rebuilding diff queries.
Analyze raw and replacement-aware changes, query files and metrics, evaluate
policy, and plan or apply GitHub labels and owned comments. The user does not
need to name diffdevil.
compatibility: >-
CLI execution needs Node.js 22 or newer; local Git sources also need Git.
GitHub operations need network access and the appropriate host credentials.
Local sources and saved reports can be used offline.
metadata:Adapts the one-file workflow to existing automation, explains its permissions and verifies the selected event and effects.
Set up diffdevil GitHub Actions for this repository by following https://diffdevil.dev/setup/actions.md exactly.What the agent will do
Every value states how it was established. A convenient number is not worth inventing certainty, so exact, bounded, unknown and unmeasurable stay different words in every output.
= exact178
Every included edit block was observed.
≈ bounded60–70
A proven interval. When the whole interval lies inside one band, the band is still proven.
? unknown≥ 5
File set incomplete; only a lower bound. No band is invented; the rule holds, or selects only its declared unknown label.
∅ unmeasurableundefined
Lines are undefined for binary content. Shown as undefined, never as 0.
A line count does not establish importance, risk, complexity or quality. Your policy owns that judgment; diffdevil evaluates it and shows its work.
Help fund development, maintenance, and the ideas behind Wolfsblvt Works.