AWS S3 MCP Server

s3_presign_get

Generate a presigned URL to download an S3 object securely. Specify bucket, key, and expiration time to get a time-limited access link.

Instructions

Generate a presigned URL for downloading an object from S3

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>",
      "key": "<key>"
    },
    "name": "s3_presign_get"
  }
}

Input Schema

Name	Required	Description
`key`	Yes	The object key
`bucket`	Yes	The name of the S3 bucket
`expiresIn`	No	URL expiration time in seconds (default: 3600, max: 604800)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Aug 1, 2026

TDQS

A3.5/5.0

Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It only states the action, but does not mention permissions required, side effects (e.g., no object modification), whether object existence is validated, or what the returned URL contains. Minimal behavioral context.

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?

A single, front-loaded sentence that precisely communicates the tool's function without any filler or redundancy.

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?

The tool is simple with detailed schema, but no output schema is present and the description does not explicitly state that the return value is the presigned URL string. However, given the low complexity and clear purpose, it is minimally complete.

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?

All three parameters (bucket, key, expiresIn) are fully described in the schema with defaults and max for expiresIn. The description adds no additional parameter meaning beyond what the schema provides, matching the baseline for high schema coverage.

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?

Description clearly states the specific action: 'Generate a presigned URL for downloading an object from S3.' It identifies the resource (S3 object), the operation (presign for download), and is distinct from sibling list tools.

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 when-to-use guidance or mention of alternatives, but the sibling tools (s3_list_buckets, s3_list_objects) are semantically different, making the intended use case for generating downloadable links implied. The description does not provide exclusions or prerequisites.

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

Deploy Server