Modkeel

Which mod crashed Minecraft

diagnose_crash

Read-onlyIdempotent

Find the mod most likely behind a modded Minecraft crash (Fabric, NeoForge, Forge). Use it whenever the user shares a crash report or latest.log or says the game will not start. It is the only tool that reads logs, and it adds what the file does not hold: it checks every installed mod against the Modkeel lab (pairs in the pack that clashed, jars that crashed on that Minecraft version), says how many other players hit the same crash and which fix worked for them (when 10+ did), counts lab runs of each suspect, and ranks suspects by evidence (mixin, trace, missing class) with a confidence level (NONE when nothing points at a mod). It also returns a fix guide and, when the log names the Minecraft version and loader, the build to install for the suspect and for every installed mod the lab saw crash on that version, so no follow-up call is needed. Pass the whole file as text, unedited: trimming it loses the mod list; or, when the user gave a link to a paste (mclo.gs, pastebin.com, paste.ee, gist.github.com, modkeel.com), pass url instead and Modkeel fetches it. Text with no crash in it comes back as an error to fix and retry. Up to 4 MB; read and dropped, never stored.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "diagnose_crash"
  }
}

Input Schema

Name	Required	Description	Default
`url`	No	A link to the crash report or log on a paste site (mclo.gs, pastebin.com, paste.ee, gist.github.com, modkeel.com), e.g. https://mclo.gs/abc123. Modkeel downloads the raw text itself. Give text or url.
`text`	No	The full crash report (crash-reports/crash-*.txt, from '---- Minecraft Crash Report ----') or logs/latest.log, unedited. Up to 4 MB. Give text or url.

Output Schema

Name	Required	Description
`mc`	No
`kind`	Yes
`pack`	No	The installed mods checked against the lab, beyond this crash.
`error`	No	The root exception and its message.
`guide`	Yes	How to fix this kind of crash.
`loader`	No
`source`	Yes
`in_game`	No	The same diagnosis inside the game, for players who crash often.
`players`	No	What other players' reports of this same crash say (Modkeel Companion reports, monthly snapshot); null below 10 players.
`replace`	No	The build to install for the first suspect, then for every installed mod whose jar crashed in the lab on this version (the next crash), as find_mod_download gives it; null when the version or loader is unknown or Modrinth is down.
`suspects`	Yes	Most likely first; empty when no mod is implicated.
`next_step`	No	What to replace and with what, one sentence per mod; tell the user all of it. Null when the version or loader is unknown.
`signature`	No	Stable id of this crash shape.
`confidence`	Yes	How sure the first suspect is the cause.
`description`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 13, 2026

changedOutput schema / properties / replace / items / properties / status / enum

Previous value: -[
-  "official",
-  "port",
-  "older_build",
-  "other_loader",
-  "none"
-]New value: +[
+  "official",
+  "port",
+  "older_build",
+  "build_from_source",
+  "other_loader",
+  "none"
+]

Changed1 schema field changedOct 13, 2026

changedOutput schema / properties / replace / items / properties / status / enum

Previous value: -[
-  "official",
-  "port",
-  "other_loader",
-  "none"
-]New value: +[
+  "official",
+  "port",
+  "older_build",
+  "other_loader",
+  "none"
+]

Changed4 schema fields changedOct 13, 2026

changedOutput schema / properties / pack / properties / crashed / description

Previous value: -"Installed mods whose jar crashed in a lab run."New value: +"Installed mods whose jar crashed in a lab run (the same version as installed, when the report names it)."

addedOutput schema / properties / pack / properties / crashed / items / properties / runs / items / properties / file
```
Added value: +{
+  "description": "The jar that crashed.",
+  "type": [
+    "string",
+    "null"
+  ]
+}
```
addedOutput schema / properties / pack / properties / crashed / items / properties / runs / items / properties / loader
```
Added value: +{
+  "type": [
+    "string",
+    "null"
+  ]
+}
```
addedOutput schema / properties / pack / properties / crashed / items / properties / runs / items / properties / version
```
Added value: +{
+  "description": "That jar's own version.",
+  "type": [
+    "string",
+    "null"
+  ]
+}
```

Changed2 schema fields changedOct 12, 2026

changedOutput schema / properties / next_step / description

Previous value: -"The follow-up call that gets the first suspect a build for this Minecraft version and loader, when both are known."New value: +"What to replace and with what, one sentence per mod; tell the user all of it. Null when the version or loader is unknown."

addedOutput schema / properties / replace

Added value: +{
+  "description": "The build to install for the first suspect, then for every installed mod whose jar crashed in the lab on this version (the next crash), as find_mod_download gives it; null when the version or loader is unknown or Modrinth is down.",
+  "items": {
+    "properties": {
+      "file": {
+        "properties": {
+          "filename": {
+            "type": "string"
+          },
+          "url": {
+            "type": "string"
+          }
+        },
+        "type": [
+          "object",
+          "null"
+        ]
+      },
+      "mod": {
+        "type": "string"
+      },
+      "next_step": {
+        "type": "string"
+      },
+      "page": {
+        "type": [
+          "string",
+          "null"
+        ]
+      },
+      "status": {
+        "enum": [
+          "official",
+          "port",
+          "other_loader",
+          "none"
+        ],
+        "type": "string"
+      }
+    },
+    "type": "object"
+  },
+  "type": [
+    "array",
+    "null"
+  ]
+}

Changed3 schema fields changedOct 12, 2026

changedInput schema / properties / text / description

Previous value: -"The full crash report (crash-reports/crash-*.txt, from '---- Minecraft Crash Report ----') or logs/latest.log, unedited. Up to 4 MB."New value: +"The full crash report (crash-reports/crash-*.txt, from '---- Minecraft Crash Report ----') or logs/latest.log, unedited. Up to 4 MB. Give text or url."

addedInput schema / properties / url

Added value: +{
+  "description": "A link to the crash report or log on a paste site (mclo.gs, pastebin.com, paste.ee, gist.github.com, modkeel.com), e.g. https://mclo.gs/abc123. Modkeel downloads the raw text itself. Give text or url.",
+  "type": "string"
+}

removedInput schema / required
```
Removed value: -[
-  "text"
-]
```

Changed2 schema fields changedOct 9, 2026

addedOutput schema / properties / pack

Added value: +{
+  "description": "The installed mods checked against the lab, beyond this crash.",
+  "properties": {
+    "clashes": {
+      "description": "Pairs in the pack that clashed in a lab run.",
+      "items": {
+        "properties": {
+          "mods": {
+            "items": {
+              "type": "string"
+            },
+            "type": "array"
+          },
+          "runs": {
+            "items": {
+              "properties": {
+                "detail": {
+                  "description": "What the lab saw, in words.",
+                  "type": "string"
+                },
+                "env": {
+                  "type": "string"
+                },
+                "mc": {
+                  "type": "string"
+                },
+                "source": {
+                  "description": "Which lab check produced the run.",
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            },
+            "type": "array"
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "crashed": {
+      "description": "Installed mods whose jar crashed in a lab run.",
+      "items": {
+        "properties": {
+          "mod": {
+            "type": "string"
+          },
+          "runs": {
+            "items": {
+              "properties": {
+                "detail": {
+                  "description": "What the lab saw, in words.",
+                  "type": "string"
+                },
+                "env": {
+                  "type": "string"
+                },
+                "mc": {
+                  "type": "string"
+                },
+                "source": {
+                  "description": "Which lab check produced the run.",
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            },
+            "type": "array"
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "mods": {
+      "description": "Mods read from the report's mod list.",
+      "type": "integer"
+    },
+    "pairs_tested": {
+      "description": "Pairs of the pack the lab ran.",
+      "type": "integer"
+    }
+  },
+  "type": "object"
+}

addedOutput schema / properties / players

Added value: +{
+  "description": "What other players' reports of this same crash say (Modkeel Companion reports, monthly snapshot); null below 10 players.",
+  "properties": {
+    "as_of": {
+      "description": "Month of the snapshot, YYYY-MM.",
+      "type": "string"
+    },
+    "fixes": {
+      "description": "Fixes 10+ players chose, and for how many it held.",
+      "items": {
+        "properties": {
+          "title": {
+            "type": "string"
+          },
+          "worked": {
+            "enum": [
+              "most",
+              "more than half",
+              "some",
+              "few"
+            ],
+            "type": "string"
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "seen": {
+      "description": "How many players reported it, as a band.",
+      "type": "string"
+    }
+  },
+  "type": [
+    "object",
+    "null"
+  ]
+}

Changed2 schema fields changedOct 9, 2026

addedOutput schema / properties / in_game

Added value: +{
+  "description": "The same diagnosis inside the game, for players who crash often.",
+  "type": "string"
+}

addedOutput schema / properties / next_step

Added value: +{
+  "description": "The follow-up call that gets the first suspect a build for this Minecraft version and loader, when both are known.",
+  "type": [
+    "string",
+    "null"
+  ]
+}

Changed2 schema fields changedOct 9, 2026

changedInput schema / properties / text / description

Previous value: -"Crash report or latest.log, unedited."New value: +"The full crash report (crash-reports/crash-*.txt, from '---- Minecraft Crash Report ----') or logs/latest.log, unedited. Up to 4 MB."

changedOutput schema / properties / suspects / description

Previous value: -"Most likely first."New value: +"Most likely first; empty when no mod is implicated."

First observedOct 3, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations cover the safety profile (readOnly, idempotent, non-destructive, open-world), and the description adds substantial context beyond them: cross-checking against the Modkeel lab, the 10+ player threshold for fix reporting, a NONE confidence fallback, an error on logs containing no crash, a 4 MB cap, and 'read and dropped, never stored.' That is a rich disclosure of behavior, limits, and data handling.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose and trigger, and nearly every clause carries operational information. It is a dense single paragraph that runs long, but the length is justified by the tool's complexity rather than padding.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Even though an output schema exists, the description covers inputs, the text/url choice, size limits, error behavior, privacy, and the shape of the ranking output. Nothing an agent needs to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the schema already documents both parameters and the paste-site list. The description still adds real meaning the schema lacks: 'Pass the whole file as text, unedited: trimming it loses the mod list,' which tells the agent why fidelity matters.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and outcome ('Find the mod most likely behind a modded Minecraft crash') and names the supported loaders. It also separates itself from siblings with 'It is the only tool that reads logs,' so an agent can tell it apart from check_mod_list, check_mod_pair, and get_mod_runs without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit trigger conditions ('whenever the user shares a crash report or latest.log or says the game will not start') and effectively excludes alternatives by declaring itself the only log-reading tool. The url-vs-text branch is spelled out with the exact paste sites that select the url path.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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