S3 MCP Server

list-objects

Retrieve a list of objects from an AWS S3 bucket, with optional prefix filtering and maxKeys limit to control results.

Instructions

List objects in an S3 bucket

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "bucket": "<bucket>"
    },
    "name": "list-objects"
  }
}

Input Schema

Name	Required	Description
`bucket`	Yes	Name of the S3 bucket
`prefix`	No	Prefix to filter objects (like a folder)
`maxKeys`	No	Maximum number of objects to return

Schema Changelog

Changes observed during successful MCP inspections.

Changed5 schema fields changedv1.0.0Jan 2, 2026

removedInput schema / additionalProperties
```
Removed value: -false
```

addedInput schema / properties / maxKeys / anyOf

Added value: +[
+  {
+    "type": "number"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / maxKeys / type
```
Removed value: -[
-  "number",
-  "null"
-]
```

addedInput schema / properties / prefix / anyOf

Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

removedInput schema / properties / prefix / type
```
Removed value: -[
-  "string",
-  "null"
-]
```

First observedAug 18, 2025

TDQS

B3.3/5.0

Behavior2/5

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

With no annotations, the description carries full burden of behavioral disclosure. It does not mention pagination, performance implications, error handling, or that it is a read-only operation. Minimal behavioral insight beyond the action itself.

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?

The description is a single sentence, very concise. However, it could include more useful information without becoming overly verbose.

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

Completeness2/5

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

Given no output schema and no annotations, the description is incomplete. It does not describe the output format, pagination behavior, or error cases, leaving the agent with insufficient context.

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

Parameters3/5

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

Schema coverage is 100% (all parameters have descriptions). The description adds no additional meaning beyond the schema; baseline score of 3 is appropriate.

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 'List objects in an S3 bucket' uses a specific verb and resource, clearly distinguishing it from siblings 'get-object' (gets a single object) and 'list-buckets' (lists all buckets).

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

Usage Guidelines3/5

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

No explicit guidance on when to use this tool vs alternatives, or how to apply parameters like prefix or maxKeys. The purpose is clear but the description lacks usage context.

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

Deploy Server