A Model Context Protocol (MCP) server that exposes japicmp as an AI tool. Connect it to Claude Desktop (or any MCP-compatible client) and ask your AI assistant to compare the APIs of any two Maven artifact versions — directly from Maven Central.
The server provides two tools:
compareJavaApi— downloads two JAR versions from Maven Central and compares their APIscompareLocalJars— compares two local JAR files on disk
Both run a full japicmp comparison and return a Markdown compatibility report with semver classification, a summary table, and detailed per-class breakdowns.
"Compare
com.github.siom79.japicmp:japicmpversion 0.25.0 with 0.26.0 using japicmp"
Here are the results of comparing japicmp 0.25.0 → 0.26.0:
---
Verdict: MAJOR (breaking changes)
The release is not binary-compatible due to changes in japicmp.cmp.JApiCmpArchive.
---
Breaking changes in JApiCmpArchive
Three methods changed their return types to Optional<T>:
┌────────────┬─────────────────┬──────────────────┐
│ Method │ Old return type │ New return type │
├────────────┼─────────────────┼──────────────────┤
│ getBytes() │ byte[] │ Optional │
├────────────┼─────────────────┼──────────────────┤
│ getFile() │ File │ Optional<File> │
├────────────┼─────────────────┼──────────────────┤
│ getName() │ String │ Optional<String> │
└────────────┴─────────────────┴──────────────────┘
These are binary and source incompatible — any code calling these methods needs to be updated to unwrap the Optional.
---
Other modified classes (no compatibility changes)
The following classes were modified but remain fully binary-, source-, and serialization-compatible:
- japicmp.config.Options — field N_A modifier changed to public static final
- japicmp.model.JApiBehavior
- japicmp.model.JApiClass
- japicmp.model.JApiField
---
Summary: The only breaking change is the JApiCmpArchive return type wrapping in Optional. If you use that class directly, update call sites to handle Optional
results. |
The report identifies that JApiCmpArchive.getFile(), getBytes(), and getName() changed their return types to Optional<T> — a binary-incompatible change requiring a semver MAJOR bump.
- Java 25+
You can download the latest release here.
- Maven 3.9+
mvn packageThis produces target/japicmp-mcp-server-0.0.4-SNAPSHOT.jar.
Add the server to your .mcp.json:
{
"mcpServers": {
"japicmp": {
"command": "java",
"args": ["-jar", "/path/to/japicmp-mcp-server-0.0.4-SNAPSHOT.jar"]
}
}
}Then restart your CLI. Both tools will be available automatically.
Compares two Maven artifacts for API compatibility using japicmp. Returns a Markdown report.
| Parameter | Type | Description |
|---|---|---|
oldGroupId |
string | GroupId of the old artifact (e.g. com.example) |
oldArtifactId |
string | ArtifactId of the old artifact |
oldVersion |
string | Version of the old artifact (e.g. 1.0.0) |
newGroupId |
string | GroupId of the new artifact |
newArtifactId |
string | ArtifactId of the new artifact |
newVersion |
string | Version of the new artifact |
onlyModified |
boolean | Only include modified API elements in the report |
onlyBinaryIncompatible |
boolean | Only include binary-incompatible changes in the report |
Both artifacts must be available on Maven Central.
Compares two local JAR files for API compatibility using japicmp. Returns a Markdown report.
| Parameter | Type | Description |
|---|---|---|
oldJarPath |
string | Absolute path to the old JAR file |
newJarPath |
string | Absolute path to the new JAR file |
onlyModified |
boolean | Only include modified API elements in the report |
onlyBinaryIncompatible |
boolean | Only include binary-incompatible changes in the report |
Both paths must be absolute and point to readable .jar files.
"Compare
/home/user/Downloads/japicmp-0.24.0.jarwith/home/user/Downloads/japicmp-0.25.0.jarusing japicmp"
## Compatibility Report: japicmp 0.24.0 → 0.25.0
Verdict: MAJOR (breaking changes)
Breaking change in japicmp.compat.CompatibilityChanges:
Removed: CompatibilityChanges(JarArchiveComparator)
Added: CompatibilityChanges(JarArchiveComparator, JarArchiveComparatorOptions)
New method in japicmp.util.FileHelper (compatible):
Added: static public String guessVersion(File)
| Component | Version |
|---|---|
| Java | 25 |
| Spring Boot | 4.0.6 |
| Spring AI MCP Server | 1.0.0 |
| japicmp | 0.26.0 |
| Transport | stdio |
Same as the parent japicmpweb project.
