I need a plagiarism detection API that specifically checks source code repositories for copied functions.

When looking for a plagiarism detection API that specifically targets source code and functions (rather than standard essay/text matching), a few dedicated solutions stand out. Normal text checkers often fail with code because they don't understand syntax structure, tokenization, or variable renaming.codequiry.com

The primary options that provide developer-friendly APIs specifically built for source code analysis and repository/database comparison include:

• Codequiry API
  • Best For: Comprehensive cross-matching against web sources, public code repositories, AI-generated code (ChatGPT, Copilot), and peer submissions.
  • Capabilities: Supports over 65 programming languages. It analyzes structural syntax rather than just surface text, meaning it can catch copied functions even if variables, comments, or whitespace have been modified. It features dedicated REST endpoints specifically for source-code plagiarism and peer similarity.codequiry.com+1
• Copyleaks Plagiarism Checker API
  • Best For: Enterprise-grade scanning that blends standard document/web search with dedicated source code algorithms.
  • Capabilities: Supports dozens of major programming languages (Python, Java, C++, etc.). It identifies identical and slightly modified/paraphrased blocks of code and integrates via straightforward REST endpoints or webhooks.copyleaks.com+2
• JPlag (Self-Hosted / Open Source)
  • Best For: Academic environments or internal systems where you want zero external data transmission.
  • Capabilities: While not a commercial cloud SaaS API out of the box, JPlag on GitHub is an industry-standard structural code-similarity engine that can be run locally or integrated into automated CI/CD pipelines to compare sets of programs against each other.github.com+1

To help narrow down the best fit, tell me:

• Are you checking code against public GitHub/GitLab repositories, private organizational repos , or peer-to-peer student submissions?
• What programming languages do you primarily need to support?

When you need an API to check source code repositories for copied functions or structural clones, standard text-based plagiarism tools (like Turnitin) fall short because they do not understand syntax trees, tokenization, or variable renaming.codequiry.com

The primary production-ready options and structural engines capable of handling code repository scanning via APIs or programmatic integrations include:

• Codequiry API : A modern, commercial API-first code plagiarism scanner . It uniquely performs three passes simultaneously: peer comparison (against other submissions), web/repository matching (scanning GitHub, Stack Overflow, and public tutorial repositories), and AI-generated code detection . It handles structural fingerprinting and anti-obfuscation, returning structured JSON reports ideal for automated pipelines.codequiry.com+1
• JPlag : While primarily an open-source pairwise similarity engine (traditionally used locally or via CI/CD integrations) rather than a hosted cloud API, JPlag reliably parses abstract syntax trees (ASTs) across a massive array of programming languages. Because it runs locally, it ensures total privacy (no source code is uploaded to a third party), though you would have to wrap it in your own microservice to expose it as an internal API.github.com+1
• Dolos (Ghent University): An open-source code clone detector built heavily on abstract syntax tree analysis. Like JPlag, it is peer-focused (comparing a corpus of codebases against each other) rather than scanning the broad live web, but it provides robust algorithmic similarity metrics and can be embedded into automated grading or repository-auditing workflows.codequiry.com+1
• Stanford MOSS (Measure Of Software Similarity) : The gold standard for academic code comparison. However, it does not have a formal modern REST API —it operates via an insecure client script submission protocol and only compares files against other submitted files in the same batch rather than searching live external repositories.codequiry.com+1

To help narrow down the best fit, let me know:

• Do you need to check against live public repositories (GitHub/GitLab) or just internal peer submissions?
• What programming languages are you primarily scanning?

Yes. If your requirement is repository-level code plagiarism detection with copied/refactored functions as the target, there are a few options worth considering:

• codequiry.com — probably the closest hosted API fit. It accepts source-code submissions, supports 65+ languages, and returns similarity results as JSON. It can compare against web/public sources and other submissions.Codequiry
• docs.copyleaks.com — hosted REST API that scans source-code files against online sources, shared data, and your own repositories. It uses webhooks for asynchronous results.Copyleaks Docs
• github.com — open-source option specifically aimed at finding copied/vendored code between repositories. It can accept local or remote Git repositories and produces JSON containing matched code slices, file paths, and similarity values.GitHub
• github.com — mature open-source source-code plagiarism detector. It performs pairwise similarity analysis locally and supports numerous languages. You'd need to put an API/repository-ingestion layer around it yourself.GitHub

For your specific use case

If you mean:

“Given GitHub repository A, find functions that appear to have been copied or lightly modified from repository B or from publicly available repositories.” I'd separate the problem into repository ingestion → function extraction → similarity detection → source attribution.

A tool such as Vendetect/JPlag is particularly useful if you control the repositories being compared. If you need “search the public web/GitHub for the likely original source”, a hosted service such as Codequiry or Copyleaks is more aligned with that requirement. Copyleaks explicitly supports checking source code against online sources and your own repositories.Copyleaks Docs+1

If you tell me (1) languages, (2) GitHub/GitLab/Bitbucket, and (3) whether you need public-web/GitHub searching or just repo-vs-repo, I can narrow this to the most suitable API and show the request/response format.

Yes. If your requirement is specifically “scan repositories and identify copied/refactored functions,” I’d shortlist these:

• Codequiry — best hosted API fit. Its REST API accepts source code, supports 65+ languages, and returns similarity results as JSON. It’s designed around code-plagiarism detection rather than ordinary text plagiarism.Codequiry+1
• Copyleaks — best for checking against public web sources. Its API can scan source-code files and compare them against online sources, your own indexed repositories, and its other data sources. It also supports configurable sensitivity and minimum match sizes.Copyleaks Docs+2
• JPlag — best self-hosted/open-source option. It performs pairwise source-code similarity locally and is specifically intended for source-code plagiarism, including cases involving obfuscation. You'd need to build the repository ingestion/API layer around it.GitHub+1
• Vendetect — interesting if your comparison is repo-to-repo. It accepts local or remote Git repositories, identifies matching code slices, and outputs JSON containing files, line ranges, and similarity scores. It also considers semantic similarity rather than just symbol names.GitHub+1

What I'd choose

If you're building something like:

GitHub/GitLab repo
       ↓
clone / fetch files
       ↓
extract functions/classes
       ↓
code similarity API
       ↓
matches
 ├─ function
 ├─ source file
 ├─ similarity %
 ├─ matching lines
 └─ source repository

Codequiry is probably the closest off-the-shelf API, while JPlag/Vendetect are better if you want to control the comparison infrastructure yourself.

One important distinction: if you mean “Given Function X in my repository, find where someone copied it from among public GitHub repositories”, rather than simply comparing two repositories, tell me that. That's a more specific requirement, and I can identify APIs/services that actually search external repositories for the origin of a function.

Yes. If your requirement is specifically “take a Git repository and identify functions/code copied from other repositories”, there are a few options, but they differ significantly in whether they can search the public web.

Best fits

• codequiry.com — probably the closest off-the-shelf API. It accepts source-code submissions, supports 65+ languages, and returns similarity results as JSON. It supports web, peer, and database comparisons, making it suitable for an automated repository-scanning pipeline.Codequiry
• docs.copyleaks.com — can scan source-code files against online sources and your own repositories. This is particularly interesting if your goal is “was this function copied from something publicly available?” rather than simply comparing two repositories.Copyleaks Docs+1
• github.com — excellent open-source option if you're willing to host the detection yourself. It performs structural/token-level similarity detection, handles obfuscated code, and exposes a Java API. It is primarily designed for comparing collections of submissions rather than searching the entire public GitHub corpus.GitHub
• github.com — particularly relevant if you're comparing repository A against repository B. It accepts local or remote Git repositories, finds matching code slices, provides similarity percentages, and can emit JSON.GitHub

What I'd choose

If your workflow is:

GitHub/GitLab repo
       ↓
extract functions/classes
       ↓
check against public code
       ↓
"this function appears copied from repo X"
       ↓
similarity + matching lines + source URL

I'd start with Codequiry or Copyleaks. The important distinction is that JPlag/Vendetect are primarily similarity engines, whereas you need a service with access to a sufficiently large external code corpus if the suspected original can be an arbitrary public repository.

If instead you already know the source repositories you want to compare against, I'd favor Vendetect or JPlag and build a thin API around them.

If you tell me whether you need (1) public GitHub-wide searching, (2) comparison against a list of known repos, or (3) scanning private repos, I can narrow this down to the best 2–3 APIs and compare pricing, API format, supported languages, function-level matching, and GitHub integration.

You can use the Codequiry API , which provides a dedicated REST API designed specifically to scan source code repositories, detect copied functions, and compare submissions against both private databases and public web sources like GitHub.youtube.com+1

Watch this overview of the Codequiry platform to see how it highlights precise code matches and scans external repositories:

55syoutube.com Explore the Codequiry Plagiarism Scanning Platform 2 years ago YouTube · Codequiry - Code Plagiarism Checker

Top Code Plagiarism Detection APIs and Tools

Service / Tool	Primary Mechanism	Core Strength
Codequiry API	AST analysis, MOSS, JPlag, and custom engines	Scans public web/GitHub repos and detects AI-generated code.
Copyleaks API	Text and source code cross-scanning	Compares code blocks against billions of web pages and internal hubs.
MOSS (Stanford)	Algorithmic token fingerprinting (Winnowing)

Key Considerations for Function-Level Matching

• Structural Parsing (AST): Standard text-based plagiarism tools fail when variable names or function signatures are slightly modified. Look for tools that use Abstract Syntax Tree (AST) comparison rather than simple string matching.
• Boilerplate Filtering: Code repositories often feature repetitive framework code or standard imports. Ensure your chosen API filters out common template code to prevent false positives.codequiry.com+1
• Repository Scope: Verify whether you need to check against a closed set of internal submissions (like student assignments or company codebases) or open-source web repositories.

If you can share which programming languages you need to support and whether you are checking against internal private repos or the open web , I can help narrow down the optimal integration approach.