MCP server opendrs

opendrs: PR blast radius analyzer and risk score for safe auto-approval

A calibrated 0-1 risk score for every pull request, so AI-reviewed, low-blast-radius PRs can be auto-approved into the merge queue while risky ones still wait for a human.

AI agents now write and review code faster than people can read it, so human review has become the bottleneck. Most pull requests are low risk, and a few cause most incidents. opendrs measures each PR's blast radius and risk: what the change touches, how many files depend on it, the history of the files it changes, author experience, missing tests and critical paths. It turns that into a 0-1 score using signals from your own git history. A team then sets a policy. For example, a PR that scores below 0.3 and has passed an AI review (Claude, CodeRabbit, Copilot or any check run) is approved and sent to the merge queue or auto-merge. Riskier PRs still wait for a human. The approach follows Meta's Diff Risk Score (DRS); opendrs is an independent, open-source implementation that runs in any git repository, with no service to host.

Contents: Install · Quick start · How it works · Features · Results · CLI and MCP · Documentation · Limitations · Compared with other tools · Prior art

Install

Use it as	Command	Details
GitHub Action	uses: error-path/opendrs@v0 (Marketplace)	Comments, labels and, optionally, approves and merges. GitHub Action reference
CLI	npx @error-path/opendrs score	CLI, MCP server, Claude Code plugin and agent skill
MCP server (any agent)	npx -y @error-path/opendrs mcp	Tools: score_diff, explain_file_risk, list_hotspots, suggest_reviewers
Claude Code plugin (skill plus MCP server)	/plugin marketplace add error-path/opendrs, then /plugin install opendrs@opendrs
Agent skill (Claude Code, Cursor, Codex and others)	npx skills add error-path/opendrs	plugin/skills/opendrs/SKILL.md
Docker (MCP server over stdio)	docker build -t opendrs . && docker run -i --rm -v "$PWD:/repo" opendrs	Mount the repository to score at /repo

Website and guides: error-path.github.io/opendrs.

Quick start

Score your current branch against the default branch. No configuration or API key is needed:

npx @error-path/opendrs score

You get a score, a tier (green, yellow or red), the signals that drove it with their evidence, and the policy decision. --json prints the full result, and --fail-above 0.6 makes the command exit 1 above a threshold.

To score every pull request, add .github/workflows/opendrs.yml (or run npx @error-path/opendrs init):

name: opendrs
on:
  pull_request:
    types: [opened, synchronize, reopened, ready_for_review, labeled, unlabeled]
permissions:
  contents: read
  pull-requests: write
  checks: read
jobs:
  opendrs:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
        with:
          fetch-depth: 0   # required: the score reads past commits and authors
      - uses: error-path/opendrs@v0

This only comments and labels. Approval is off until you turn it on in .opendrs.yml on your default branch; see how to auto-approve low-risk PRs and the GitHub Action reference.

How it works

flowchart LR
  diff["git diff<br/>merge-base...head"] --> signals
  hist["git history"] --> signals
  imports["import graph"] --> signals
  llm["LLM judge<br/>(optional)"] --> signals
  signals["Signals<br/>each with evidence<br/>and provenance"] --> model["Logistic model<br/>score = sigmoid(b + Σ w·x)"]
  model --> tier["Tier<br/>green / yellow / red"]
  tier --> policy["Policy<br/>blocks, size cap, unknowns,<br/>AI review, sampling"]
  policy --> decision["auto-approve<br/>deferred-review<br/>waiting-ai-review<br/>human-review"]

1. Signals. Each signal provider reads the diff, the history and the import graph and emits features: size, how spread out the change is, past fixes and reverts in the touched files, the author's experience with them, complexity, blast radius (transitive dependents), critical paths and missing tests. Every signal records how it was obtained (observed, derived, inferred or unknown) and the evidence behind it. All signals
2. Model. A logistic regression turns the features into a probability. Each signal's contribution w·x is reported, so you can see why a PR scored what it did. Out of the box the weights are hand-set priors; opendrs calibrate fits them to your repository. Calibration and backtesting
3. Tiers. The score maps to green, yellow or red, mirroring Meta's gates. Thresholds can be absolute scores or percentiles of your own history.
4. Policy. Ordered rules turn the score into a decision. Policy and safety rails

Where opendrs sits in your PR flow

A PR now often gets two rounds of AI review before a human looks at it. Those rounds catch local defects: typos, missing null checks, an obvious off-by-one. By the time a human opens the PR, that work is done, and what is left is a design and architecture judgment call made with less context than before. opendrs is built for that moment: it tells the final human how much attention the PR needs and names up to five architecture and history facts — a new import between modules, a broken public contract, a file that usually changes with one the PR didn't touch — that neither the editor nor the AI review comments showed. See the captain brief.

Features

Feature	What it does	Default	Docs
Risk signals	Size, spread, file history, author experience, complexity, blast radius, critical paths, tests, language	on	Signals
Calibration and backtest	Fit the weights to your history and measure capture at 5 / 10 / 50 % gated	run on demand	Calibration
Hard blocks and safety rails	Blocked paths, binaries, submodules, self-modification guard, sampling, stale-approval checks	on	Policy
Auto-approval	Approve green PRs after your AI review passes, then auto-merge or the merge queue	off	Auto-approve guide
LLM judge	Classifies every hunk into safe or risk categories; can only raise the score	off	LLM judge
requireSafe gate	Auto-approve only when the judge calls every hunk safe with enough confidence	off	LLM judge
Per-source policy	Human, bot or AI-agent PRs get their own stricter green, daily cap and track record	off	Policy
Deferred review	A PR just above green lands now and gets a post-merge review	off	Policy
Landing delay	An eligible PR waits before approval, so a human can veto	off	Policy
Freeze windows	Suspend or tighten auto-approval on weekends or peak dates	off	Policy
Content blocklist	Regexes on added lines send a PR to a human	off	Configuration
Reviewer assignment	One of the top three experts is asked to review risky PRs	on in the Action	Policy
Hotspots	Rank files by risk at rest	run on demand	CLI and MCP
Review brief	Ranks hunks to read first, fixed check questions, safe-to-skim list, hard-rule reasons — recipes for claude-code-action, Bugbot, CodeRabbit (limited), Copilot and Codex (paste)	on	LLM reviewers, CLI and MCP
Pre-PR self-check	Lists the ids an author agent should fix or explain before opening the PR; opendrs reads the verdicts back from the head commit and adds one advisory line, never part of the gate	off	Self-check recipe
Verification pass	One batched LLM call re-checks every captain fact, review-first hunk and check with fresh context and keeps, drops or downgrades each one; never changes the score, tier or policy	off	Verification pass
Incident feedback	opendrs feedback records incidents for calibration	run on demand	Calibration

Every setting lives in .opendrs.yml, read from the base branch so a PR cannot loosen its own gate: configuration reference.

Results

Benchmark	Result	Details
ApacheJIT (15 Apache Java projects, official 2017–2019 test years, apache/hadoop left out because it has no positive labels)	Calibrated opendrs: AUC 0.823; catches 67 % of buggy commits in its riskiest 30 %, on par with a regression on the classic JIT metrics (0.821, 66 %)	Results on ApacheJIT
ApacheJIT with the LLM judge (Claude Sonnet 5, 800 sampled test commits)	At confidence 8, the commits the judge calls all-safe are buggy at 5.3 %, against a 25.5 % base rate	With the structured LLM judge
27 public repositories (calibrate, then backtest)	Calibration beat the default priors on held-out commits in all nine repositories of the first run	Benchmark results

CLI and MCP

Command	What it does
opendrs score	Score merge-base(base, head)..head
opendrs explain <file>	A file's history, fixes, authors, dependents and path policy
opendrs hotspots	Rank files by risk at rest
opendrs calibrate / opendrs backtest	Fit the model to your history; compare default and calibrated models
opendrs feedback	Record an incident in .opendrs/incidents.jsonl
opendrs init	Write a commented .opendrs.yml and a comment-only workflow
opendrs mcp	Run the MCP server

Flags, exit codes, MCP tools and the agent skill: CLI, MCP server, Claude Code plugin and agent skill.

Documentation

Page	Read it when you want to
Auto-approve low-risk PRs	set up a risk-based approval gate step by step
GitHub Action reference	look up inputs, outputs, permissions, branch rules and the scheduled sweep
Policy and safety rails	know exactly why a PR was or was not approved
Configuration reference	change .opendrs.yml
Risk signals	see what opendrs measures and how
What is the blast radius of a PR?	understand blast radius
LLM judge	turn on the optional LLM judge or the requireSafe gate
Feeding the review brief to an LLM reviewer	get opendrs's findings in front of Claude Code, claude-code-action, Bugbot, CodeRabbit, Copilot or Codex
The captain brief	know what the final human reviewer sees: priority, reviewer, and the architecture and history facts
Verification pass	turn on an LLM re-check of the brief's facts before a human reads them
Calibration and backtesting	fit the model to your repository and choose thresholds
Benchmark results	see how opendrs ranks risk on public repositories
Experiments	see what we tried and what did not work
CLI, MCP server, Claude Code plugin and agent skill	run opendrs locally or from an agent
Known limitations	know what opendrs cannot see
Compared with other tools	choose between opendrs and other PR risk tools
CHANGELOG	see what changed in each release

Limitations

• The default weights are not fit to your code. Run backtest before trusting them, and calibrate when you have enough history.
• Labels are proxies for incidents, and small repositories give unstable numbers.
• The score is not a code review. It estimates the chance of an incident, not whether the change is correct.

The full list: known limitations.

Compared with other tools

If you want	Use
A risk gate that approves or merges low-risk PRs, measured on your own history, with no service to host	opendrs
An LLM's judgment of each PR as the gate	PR-Agent's auto-approval, Merge Steward or MergeShield Risk Check; opendrs's optional LLM judge can only raise the score
Approval inside Cursor's cloud on a team plan	Cursor approval agents
Review comments on the code	An AI reviewer (Claude Code, CodeRabbit, PR-Agent), with opendrs running after it

The full comparison, with how each tool scores and where it runs, is at error-path.github.io/opendrs/alternatives.html.

Prior art and credits

• Meta's Diff Risk Score. Diff Risk Score: AI-driven risk-aware software development (Engineering at Meta, 2025) and Abreu et al., Moving Faster and Reducing Risk: Using LLMs in Release Deployment (2024). The feature set, the tiered gates and the capture-at-X %-gated metric come from this work. opendrs is not affiliated with Meta.
• Meta's RADAR. Adams et al., Automating Low-Risk Code Review at Meta (2026): the structured LLM reviewer with safe and risk categories, per-source policy (daily caps, track record), deferred review, the landing delay and the content blocklist follow this paper. Related Meta work behind hotspots and reviewer assignment: Mockus et al., "Metrics Driven Reengineering and Continuous Code Improvement at Meta" (ASE 2025); Paraspatki et al., "Code Reviewer Recommendation for High Risk Diffs at Scale" (FSE Companion 2026); Rigby et al., Improving Code Reviewer Recommendation (TOSEM 2025).
• Benchmarks and peers. Keshavarz and Nagappan, ApacheJIT (MSR 2022), the dataset bench/apachejit/ scores; Sayedsalehi, Rigby and Mockus, DRS-OSS (2025), the open-source LLM counterpart whose numbers the benchmark quotes.
• Just-in-time defect prediction and SZZ. Mockus and Weiss, "Predicting risk of software changes" (2000); Śliwerski, Zimmermann and Zeller, "When do changes induce fixes?" (2005); Kamei et al., "A large-scale empirical study of just-in-time quality assurance" (2013). The change-level features and the SZZ-style labelling follow this literature.
• REA (morluto/rea). opendrs adopts REA's evidence-first method: every conclusion is marked observed, derived, inferred or unknown, and unknown is never treated as safe. It also follows REA's layering of domain types, providers, a shared engine and thin adapters.

License

MIT