s3-mcp

List S3 objects

s3_list_objects

Read-only

List objects in an S3 bucket with optional prefix and delimiter for folder-style browsing. Use it to explore bucket contents or paginate large result sets.

Instructions

List objects in a bucket. Optional prefix/delimiter for folder-style browsing. Note: S3 ListObjectsV2 does not return user metadata — use s3_head_object for that.

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": "s3_list_objects"
  }
}

Input Schema

Name	Required	Description
`bucket`	Yes	Bucket name
`prefix`	No	Key prefix filter
`maxKeys`	No	Max keys to return (default 1000)
`delimiter`	No	Delimiter for common prefixes (e.g. "/")
`continuationToken`	No	Pagination token from a previous response

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Sep 13, 2026

TDQS

A3.9/5.0

Behavior3/5

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

Annotations already declare readOnlyHint/openWorldHint/destructiveHint=false, so the safety profile is covered. The description adds a valuable limitation (metadata not returned) but says nothing about pagination behavior despite exposing a continuationToken, so added behavioral context is partial.

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?

Three short, front-loaded sentences with zero filler; purpose first, then the browsing idiom, then the sibling-routing caveat.

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

Completeness3/5

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

Adequate for a read-only list tool whose annotations carry safety, but for a paginated list with a continuationToken parameter and no output schema, an agent gets no description of what the response contains or how to page. This is a meaningful gap for correct invocation.

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 description coverage is 100%, so parameters are already fully documented. The description's mention of prefix/delimiter semantics and the metadata note adds marginal value but no syntax or format detail beyond the schema; baseline 3 applies.

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 resource ('List objects in a bucket') and names the sibling it is not (s3_head_object), with scope clarified by prefix/delimiter for folder-style browsing. An agent can distinguish this from s3_list_buckets and neighboring object tools without opening schemas.

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?

Explicitly routes metadata lookups to s3_head_object and implies folder-style browsing via prefix/delimiter. It does not, however, cover when-not-to-use beyond the metadata case, e.g. no guidance on choosing this over s3_list_buckets or on pagination workflows.

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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