Fiji MCP Server

Overview Schema Source Related Servers Discussions Admin

list_extensions

Read-onlyIdempotent

Retrieve names and URLs of configured ImageJ update sites to identify available extensions for microscopy image analysis.

Instructions

List configured ImageJ update sites (name and URL) when the updater classes are present. May return an empty list on minimal installs; see note field.

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": "list_extensions"
  }
}

Input Schema

Name	Required	Description	Default
No arguments

Output Schema

Name	Required	Description
`ok`	No
`extensions`	Yes
`count`	Yes
`note`	Yes	How extension list was obtained or why it may be empty.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.3May 27, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already indicate readOnlyHint and idempotentHint. The description adds that the list may be empty on minimal installs, which is useful behavioral context beyond the annotations.

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

Conciseness5/5

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

The description is two sentences, front-loaded with the main action and followed by important caveats. Every sentence adds value without unnecessary words.

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?

Given the tool's simplicity (no parameters, output schema exists), the description covers the key points: what it lists, precondition, edge case (empty on minimal installs), and a pointer to the note field. It is complete for this tool.

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?

The tool has no parameters (schema is empty), so schema description coverage is 100%. The baseline for zero parameters is 4, and the description correctly does not attempt to explain parameters.

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?

The description clearly states the tool lists configured ImageJ update sites (name and URL). It distinguishes itself from sibling listing tools like list_open_images, list_all_commands, and list_macro_templates by specifying the exact resource (update sites).

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

Usage Guidelines4/5

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

The description provides a usage condition: 'when the updater classes are present.' It also warns about possible empty lists on minimal installs. While it doesn't explicitly mention when not to use or compare to siblings, the precondition is helpful.

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