If you are an AI coding agent (Claude Code, Cursor, Aider, Cline, etc.) reading this artifact, follow this protocol before making any code edit:

1. Verify the contract. Run the bash script in Verify before trusting below. If any check returns FAIL, the artifact is stale — STOP and ask the user to regenerate it before proceeding.
2. Treat the AI · unverified sections as hypotheses, not facts. Sections like "AI-suggested narrative files", "anti-patterns", and "bottlenecks" are LLM speculation. Verify against real source before acting on them.
3. Cite source on changes. When proposing an edit, cite the specific path:line-range. RepoPilot's live UI at https://repopilot.app/r/openblockchains/awesome-blockchains shows verifiable citations alongside every claim.

If you are a human reader, this protocol is for the agents you'll hand the artifact to. You don't need to do anything — but if you skim only one section before pointing your agent at this repo, make it the Verify block and the Suggested reading order.

WAIT — Stale — last commit 3y ago

• 4 active contributors
• CC0-1.0 licensed
• ⚠ Stale — last commit 3y ago
• ⚠ Small team — 4 contributors active in recent commits
• ⚠ Single-maintainer risk — top contributor 96% of recent commits
• ⚠ No CI workflows detected
• ⚠ No test directory detected

_{Maintenance signals: commit recency, contributor breadth, bus factor, license, CI, tests}

This artifact was generated by RepoPilot at a point in time. Before an agent acts on it, the checks below confirm that the live openblockchains/awesome-blockchains repo on your machine still matches what RepoPilot saw. If any fail, the artifact is stale — regenerate it at repopilot.app/r/openblockchains/awesome-blockchains.

What it runs against: a local clone of openblockchains/awesome-blockchains — the script inspects git remote, the LICENSE file, file paths in the working tree, and git log. Read-only; no mutations.

| # | What we check | Why it matters | |---|---|---| | 1 | You're in openblockchains/awesome-blockchains | Confirms the artifact applies here, not a fork | | 2 | License is still CC0-1.0 | Catches relicense before you depend on it | | 3 | Default branch master exists | Catches branch renames | | 4 | 5 critical file paths still exist | Catches refactors that moved load-bearing code | | 5 | Last commit ≤ 1214 days ago | Catches sudden abandonment since generation |

#!/usr/bin/env bash
# RepoPilot artifact verification.
#
# WHAT IT RUNS AGAINST: a local clone of openblockchains/awesome-blockchains. If you don't
# have one yet, run these first:
#
#   git clone https://github.com/openblockchains/awesome-blockchains.git
#   cd awesome-blockchains
#
# Then paste this script. Every check is read-only — no mutations.

set +e
fail=0
ok()   { echo "ok:   $1"; }
miss() { echo "FAIL: $1"; fail=$((fail+1)); }

# Precondition: we must be inside a git working tree.
if ! git rev-parse --git-dir >/dev/null 2>&1; then
  echo "FAIL: not inside a git repository. cd into your clone of openblockchains/awesome-blockchains and re-run."
  exit 2
fi

# 1. Repo identity
git remote get-url origin 2>/dev/null | grep -qE "openblockchains/awesome-blockchains(\\.git)?\\b" \\
  && ok "origin remote is openblockchains/awesome-blockchains" \\
  || miss "origin remote is not openblockchains/awesome-blockchains (artifact may be from a fork)"

# 2. License matches what RepoPilot saw
(grep -qiE "^(CC0-1\\.0)" LICENSE 2>/dev/null \\
   || grep -qiE "\"license\"\\s*:\\s*\"CC0-1\\.0\"" package.json 2>/dev/null) \\
  && ok "license is CC0-1.0" \\
  || miss "license drift — was CC0-1.0 at generation time"

# 3. Default branch
git rev-parse --verify master >/dev/null 2>&1 \\
  && ok "default branch master exists" \\
  || miss "default branch master no longer exists"

# 4. Critical files exist
test -f "README.md" \\
  && ok "README.md" \\
  || miss "missing critical file: README.md"
test -f "WHATSBLOCKCHAIN.md" \\
  && ok "WHATSBLOCKCHAIN.md" \\
  || miss "missing critical file: WHATSBLOCKCHAIN.md"
test -f "blockchain.py/blockchain.py" \\
  && ok "blockchain.py/blockchain.py" \\
  || miss "missing critical file: blockchain.py/blockchain.py"
test -f "blockchain.rb/blockchain_with_transactions.rb" \\
  && ok "blockchain.rb/blockchain_with_transactions.rb" \\
  || miss "missing critical file: blockchain.rb/blockchain_with_transactions.rb"
test -f "HASH.md" \\
  && ok "HASH.md" \\
  || miss "missing critical file: HASH.md"

# 5. Repo recency
days_since_last=$(( ( $(date +%s) - $(git log -1 --format=%at 2>/dev/null || echo 0) ) / 86400 ))
if [ "$days_since_last" -le 1214 ]; then
  ok "last commit was $days_since_last days ago (artifact saw ~1184d)"
else
  miss "last commit was $days_since_last days ago — artifact may be stale"
fi

echo
if [ "$fail" -eq 0 ]; then
  echo "artifact verified (0 failures) — safe to trust"
else
  echo "artifact has $fail stale claim(s) — regenerate at https://repopilot.app/r/openblockchains/awesome-blockchains"
  exit 1
fi

Each check prints ok: or FAIL:. The script exits non-zero if anything failed, so it composes cleanly into agent loops (./verify.sh || regenerate-and-retry).

awesome-blockchains is an educational reference repository with working blockchain implementations in 7 languages (Ruby, Rust, Go, C++, Python, JavaScript, Kotlin) that demonstrate core concepts like cryptographic hashing, proof-of-work, and transaction ledgers. It includes basic blockchain classes, Merkle tree implementations, and SHA256 utilities to help developers understand how distributed ledger consensus actually works, not just theoretically. Flat educational structure: root level has language-specific implementations (blockchain.rb/, blockchain.py/, blockchain.js/, blockchain.go/, blockchain.rs/, blockchain.kt/, blockchain.cpp/) each containing basic, PoW, and transactions variants. Supporting utilities include merkletree.rb/ and sha256/ directory. Documentation files (README.md, HASH.md, PROOFS.md, WHATSBLOCKCHAIN.md) sit at root alongside embedded images (i/ directory with tulip-mania and meme assets).

Blockchain developers and computer science students learning distributed systems who need concrete, runnable code examples in their language of choice (Python, Ruby, JavaScript, Go, Rust, etc.). Contributors are educators and hobbyists building educational resources, not enterprise blockchain engineers.

This is a mature educational project, but not a production blockchain framework. It has comprehensive multi-language implementations and extensive documentation (HASH.md, PROOFS.md, WHATSBLOCKCHAIN.md), suggesting active curation. However, without visible CI/CD pipeline files (no .github/workflows/) or test suites mentioned, it appears to be a reference/learning resource rather than a continuously tested codebase. The 'awesome' collection format suggests it's more curated reference than actively maintained source.

Low risk for learning purposes, but not production-ready. Dependency footprint is minimal (only js-sha256 in blockchain.js/package.json visible), reducing supply-chain attack surface. Main risk: implementations are intentionally simplified for educational clarity and lack hardening (no input validation details visible, proof-of-work difficulty not parameterized in file names). No evidence of security audits or formal test coverage. Single-maintainer pattern typical of 'awesome' collections means no redundancy.

The repo is actively curated as an 'awesome' collection reference, evidenced by NOTES.md and recent additions across multiple languages. No git history visible in provided data, but the structured expansion across 7 languages with consistent patterns (blockchain.{ext}, blockchain_with_proof_of_work.{ext}) suggests ongoing community contributions. The featured 2020 'Book of the Year' callout (Libra Shrugged) in README indicates regular updates to external reference material.

Clone and navigate to your language: git clone https://github.com/openblockchains/awesome-blockchains.git && cd blockchain.rb (or .py, .js, .go, .rs, .kt, .cpp). For JavaScript: cd blockchain.js && npm install. For Ruby: cd blockchain.rb && ruby blockchain.rb. For Python: cd blockchain.py && python blockchain.py. No global build system; each language folder is self-contained.

Daily commands: Language-specific: Ruby: cd blockchain.rb && ruby blockchain.rb or ruby blockchain_with_proof_of_work.rb. Python: cd blockchain.py && python blockchain.py. JavaScript: cd blockchain.js && npm install && node blockchain.js. Go: cd blockchain.go && go run blockchain.go. Rust: cd blockchain.rs && cargo run. Kotlin: cd blockchain.kt && kotlinc blockchain.kts -script (or use IDE). C++: cd blockchain.cpp && g++ blockchain.cpp -o blockchain && ./blockchain.

• README.md — Entry point documenting the project's philosophy, multiple blockchain implementations across languages, and DIY educational approach—essential context for all contributors.
• WHATSBLOCKCHAIN.md — Foundational conceptual document explaining what blockchains are, their properties, and how they differ from traditional databases—required reading before implementing.
• blockchain.py/blockchain.py — Core reference implementation demonstrating the simplest blockchain pattern (hashing, linking, validation) used as a template across all language variants.
• blockchain.rb/blockchain_with_transactions.rb — Extended implementation showing how to add transaction data structures and business logic on top of the basic blockchain pattern.
• HASH.md — Technical documentation on cryptographic hashing fundamentals and SHA-256, critical for understanding blockchain security properties.
• PROOFS.md — Explains proof-of-work mechanisms and mining algorithms used across multiple implementations in the codebase.

• Block class (SHA-256) — Encapsulates immutable ledger entry: index, timestamp, transaction/data payload, cryptographic link to predecessor (prev_hash), and self-hash. Computes SHA-256 digest of contents.
  • Failure mode: Hash computation error → chain validation fails; tampering → hash mismatch detected on next verification
• Blockchain class (Block class, SHA-256) — Maintains ordered chain of blocks, enforces immutability by verifying each new block's prev_hash matches predecessor, rejects invalid blocks.
  • Failure mode: Missing validation → forged blocks accepted; lost prev_block reference → chain frag

Add a new blockchain implementation in a new language

1. Create new directory following pattern: blockchain.{lang}/ (e.g., blockchain.java/) (blockchain.{lang}/)
2. Implement Block class with fields: index, timestamp, data, prev_hash, hash; add compute_hash() method using SHA-256 (blockchain.{lang}/blockchain.{lang})
3. Implement Blockchain class with add_block() validation: check prev_hash matches last block's hash, verify new block's hash is valid (blockchain.{lang}/blockchain.{lang})
4. Create proof-of-work variant (optional) with nonce field, difficulty target, and mine() method incrementing nonce until hash meets target (blockchain.{lang}/blockchain_with_proof_of_work.{lang})
5. Add README.md following template in blockchain.py/README.md documenting usage and any language-specific considerations (blockchain.{lang}/README.md)

Extend a blockchain implementation with transaction support

1. Define Transaction struct/class with from, to, what (asset), qty fields (reference: blockchain.rb/blockchain_with_transactions.rb lines 1–20) (blockchain.{lang}/blockchain_with_transactions.{lang})
2. Modify Block.data to accept array of Transaction objects instead of flat strings (blockchain.{lang}/blockchain_with_transactions.{lang})
3. Update Block.compute_hash() to serialize transaction array into hash input (maintain deterministic ordering) (blockchain.{lang}/blockchain_with_transactions.{lang})
4. Add Block.next() convenience method accepting variable transaction arguments and returning new block linked to previous (blockchain.{lang}/blockchain_with_transactions.{lang})

Add mining difficulty and proof-of-work validation

1. Add nonce (int) and difficulty (int) fields to Block class; difficulty represents leading zero bits required in hash (blockchain.{lang}/blockchain_with_proof_of_work.{lang})
2. Implement mine() method: incrementing nonce and recalculating hash until hash (as integer) is less than 2^(256-difficulty) (blockchain.{lang}/blockchain_with_proof_of_work.{lang})
3. Update Blockchain.add_block() validation to verify: (1) prev_hash match, (2) hash meets difficulty target, (3) hash recomputes correctly from block data+nonce (blockchain.{lang}/blockchain_with_proof_of_work.{lang})
4. Optionally add mining benchmark (reference: sha256/hashrate.go) measuring blocks/second at given difficulty (blockchain.{lang}/benchmark.{lang})

• SHA-256 cryptographic hashing — Deterministic, collision-resistant, and computationally efficient; provides tamper-detection and immutability guarantees for blockchain integrity.
• Multi-language implementations (Python, Ruby, Go, JavaScript, Rust, C++, Kotlin) — Educational accessibility across developer communities; demonstrates that blockchain patterns are language-agnostic abstractions, not framework-dependent.
• Proof-of-work mining with difficulty adjustment — Concrete demonstration of consensus mechanism and computational cost of block creation; illustrates security-via-work paradigm.

• Single-threaded sequential mining implementations

  • Why: Simplicity and educational clarity; easier to understand block creation and validation logic without concurrency overhead.
  • Consequence: Not representative of real blockchain networks (which use thread pools, GPU acceleration, ASIC miners); benchmarks are orders of magnitude slower than production.

• In-memory blockchain storage (no persistence layer)

  • Why: Minimal dependencies and instant startup; focuses on core pattern rather than database design.
  • Consequence: Blockchain lost on process exit; not suitable for production or realistic consensus scenarios requiring state durability.

• No transaction validation, balance checking, or double-spend prevention

  • Why: Reduces complexity to focus on immutability and hashing; transaction layer is orthogonal to blockchain structure.
  • Consequence: Cannot model real-world cryptocurrency use cases; only demonstrates data structure integrity, not economic finality.

• No peer-to-peer networking or gossip protocol

  • Why: Single-node model is easiest to understand and debug; removes distributed systems complexity.
  • Consequence: No fork resolution, consensus, or decentralization; not applicable to distributed ledger scenarios.

• Production-grade cryptocurrency or smart contract platform
• Peer-to-peer network synchronization or consensus protocols
• Transaction validation, account balances, or double-spend detection
• Persistence layer or database integration
• Performance optimization for real-world mining or industrial use
• Web UI, API server, or wallet implementation

No environment variables or complex setup, but beware: (1) Difficulty parameters in PoW implementations may be set very low (e.g., leading zeros = 2 or 3) for quick demo execution—not realistic for actual consensus. (2) No input validation: sender/receiver addresses in transaction examples are plain strings, not cryptographic keys. (3) Merkle tree in merkletree.rb/ is educational only—real blockchains use more sophisticated tree structures (Bitcoin uses double SHA-256 on pairs). (4) SHA256 implementations vary by language stdlib; some repos may use different hashing variants without explicit documentation. (5) No persistence layer—all blockchains run in-memory; no database file format or serialization beyond what's shown in examples.

• Cryptographic Hash Function — The foundation of blockchain immutability: if you change one byte in a block, its hash changes completely, breaking all downstream links. This repo implements SHA256 as the hash function in every variant.
• Proof of Work (PoW) — The consensus mechanism used in blockchain_with_proof_of_work.* files; requires miners to solve a hard puzzle (find nonce with N leading zero bits in hash) to add blocks, making it expensive to attack the chain.
• Merkle Tree — Data structure implemented in merkletree.rb that allows efficient verification of large transaction sets with only O(log n) hashes; used in Bitcoin/Ethereum to summarize blocks.
• Immutability via Hash Chaining — Each block in this repo stores the previous block's hash; changing any old block rehashes it, which breaks the link for all subsequent blocks, making tampering obvious. Core to why blockchains are tamper-evident.
• Difficulty Adjustment — In blockchain_with_proof_of_work files, difficulty (number of leading zero bits required in hash) controls how long mining takes; understanding this is essential to grasping why real blockchains throttle block creation time.
• Double-Spending Problem — Blockchains solve double-spending by ordering transactions in an immutable ledger; the transaction examples in blockchain_with_transactions.rb illustrate why digital currency needs this, not just digital signatures.
• Nonce (Number Used Once) — In proof_of_work implementations, the nonce is the value miners increment to find a hash meeting difficulty requirements; understanding nonce loops is key to why mining requires computation.

• bitcoinj/bitcoinj — Production Java blockchain library that extends the educational patterns in this repo; reference for how real-world blockchain code handles keys, transactions, and network sync
• paritytech/substrate — Rust blockchain framework that builds on concepts like those in blockchain.rs/; essential for understanding how educational PoW scales to actual consensus protocols
• ethereum/go-ethereum — Go implementation of Ethereum showing how blockchain.go/ patterns evolve into a full smart-contract platform with state trees and gas metering
• openblockchains/awesome-diem — Companion awesome list focused on Diem/Libra (featured in this repo's README), covering Move language and Facebook's blockchain experiment—directly linked from main docs
• git/git — Referenced in repo description as 'the stupid content tracker with crypto hashes'—canonical example of distributed ledger using SHA-1, inspiring blockchain design parallels

To work on one of these in Claude Code or Cursor, paste: Implement the "<title>" PR idea from CLAUDE.md, working through the checklist as the task list.

Add cross-language test suite for blockchain implementations

The repo has blockchain implementations in 6+ languages (JS, Python, Ruby, Go, Rust, Kotlin, C++) but no automated tests validating they produce compatible outputs. A new contributor could create a test harness that verifies all implementations produce identical block hashes and chain validation results for the same input transactions.

• [ ] Create tests/test_vectors.json with standard test cases (genesis block, multi-block chains, invalid blocks)
• [ ] Add test runner for blockchain.js (using Jest or similar) against test_vectors.json
• [ ] Add test runner for blockchain.py against test_vectors.json
• [ ] Add test runner for blockchain.rb against test_vectors.json
• [ ] Document in tests/README.md how to verify cross-language compatibility
• [ ] Add GitHub Actions workflow to run all language tests on PR

Create unified Merkle Tree implementation reference across languages

merkletree.rb exists but there's no merkletree implementation for the other 5+ languages. This is a critical blockchain component. A contributor should implement Merkle Tree in at least JavaScript and Python to match the Ruby version, ensuring consistent behavior.

• [ ] Create merkletree.js/merkletree.js based on merkletree.rb logic, using js-sha256 dependency
• [ ] Create merkletree.js/README.md documenting the implementation with examples
• [ ] Create merkletree.py/merkletree.py with equivalent functionality
• [ ] Add unit tests in merkletree.js/test.js and merkletree.py/test.py
• [ ] Update root README.md to reference all Merkle Tree implementations

Add Proof-of-Work difficulty tests for blockchain_with_proof_of_work implementations

Every language has a blockchain_with_proof_of_work variant, but there's no validation that difficulty levels are consistent or correct. A contributor should create a dedicated test suite that verifies mining difficulty, nonce validation, and hash target checking across all PoW implementations.

• [ ] Create tests/proof_of_work_tests.md documenting PoW test scenarios (e.g., 'mining with difficulty 3 should require leading zeros')
• [ ] Add test_proof_of_work.js for blockchain.js/blockchain_with_proof_of_work.js
• [ ] Add test_proof_of_work.py for blockchain.py/blockchain_with_proof_of_work.py
• [ ] Add test_proof_of_work.rb for blockchain.rb/blockchain_with_proof_of_work.rb
• [ ] Create PoW validation examples in tests/ showing expected output for known difficulty levels
• [ ] Document any discrepancies or language-specific PoW behaviors in PROOFS.md

• Add Python implementation of Merkle tree (merkletree.rb exists but no merkletree.py): create blockchain.py/merkletree.py with same API as Ruby version and document in blockchain.py/README.md with example usage matching the tulip transaction pattern.
• Create comprehensive test suites for all language implementations: add test/ directories (test_blockchain.py, test_blockchain.js, blockchain_test.rb, blockchain_test.go) with 5-10 tests per language validating Block immutability, chain validation, and PoW difficulty scaling.
• Document consensus algorithm comparison table in PROOFS.md: add a markdown table comparing proof-of-work (shown in code), proof-of-stake, Byzantine fault tolerance with one concrete code reference per row (e.g., 'PoW: see blockchain_with_proof_of_work.rb lines 20–35 for mine() loop').

This is an educational blockchain implementation repository with moderate security concerns. The primary issue is the use of an outdated JavaScript dependency (js-sha256 v0.6.0 from 2016) which should be updated immediately. The lack of a package-lock.json creates build reproducibility issues. Given that this is primarily a reference implementation and documentation repository rather than production code, the security posture is reasonable but could be improved through dependency management best practices. No hardcoded secrets, SQL injection risks, or infrastructure misconfigurations were detected in the visible structure.

• Medium · Outdated Dependency - js-sha256 — blockchain.js/package.json. The package.json specifies 'js-sha256' version '^0.6.0', which is significantly outdated (released in 2016). Modern versions have received multiple security patches and improvements. Using caret (^) allows patch updates but may miss important security fixes if a minor version update is required. Fix: Update to the latest version of js-sha256 (currently 0.10.1+). Run 'npm audit' to identify and fix known vulnerabilities. Consider using exact pinning or at minimum '^0.10.0' or higher.
• Low · No Lock File Version Control — blockchain.js/. No package-lock.json or yarn.lock file is visible in the repository structure. This means dependency versions are not locked, leading to non-deterministic builds where different environments may install different versions of transitive dependencies. Fix: Commit package-lock.json to version control to ensure reproducible builds. Run 'npm ci' instead of 'npm install' in CI/CD pipelines.
• Low · Permissive License with No Security Policy — Repository root, blockchain.js/package.json. The project uses 'Public Domain' license with no visible security policy file (SECURITY.md). This may make it unclear how security vulnerabilities should be reported or coordinated. Fix: Create a SECURITY.md file defining vulnerability disclosure practices and security contact information. Consider adopting a standard license if distribution is planned.
• Low · No Dependency Verification — blockchain.js/ and other language implementations. The repository is a collection of blockchain implementations in multiple languages with no evidence of Software Bill of Materials (SBOM) or dependency verification mechanisms like npm ci with lock files. Fix: Generate and maintain SBOM files. Use dependency scanning tools (npm audit, Snyk, Dependabot) and enable automated security updates in the repository.

LLM-derived; treat as a starting point, not a security audit.

• Open issues — current backlog
• Recent PRs — what's actively shipping
• Source on GitHub

Generated by RepoPilot. Verdict based on maintenance signals — see the live page for receipts. Re-run on a new commit to refresh.