s3-mcp

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presign_put

Generate a pre-signed PUT URL for secure object uploads to S3, with configurable expiration up to 7 days, enabling temporary access without credentials.

Instructions

Generate a pre-signed PUT URL valid for expires_s seconds (max 604800).

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": "presign_put"
  }
}

Input Schema

Name	Required	Description	Default
`key`	Yes
`bucket`	Yes
`expires_s`	No

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 18, 2026

TDQS

C2.9/5.0

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 mentions the expiry duration and its max, but fails to disclose that the URL grants temporary write access, that it's a security token, or that it's specific to the PUT method. This is a significant gap for a tool that creates a security-sensitive URL.

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 with no unnecessary words, and the key constraint (max 604800) is front-loaded. It is concise and efficient, but the brevity contributes to the under-specification seen in other dimensions.

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?

The description omits crucial context: prerequisites (bucket must exist, key must be valid), security implications (anyone with the URL can upload until expiry), and when to use this vs alternatives. The output schema may define the return URL, but the description doesn't explain the operational context needed for correct and safe usage.

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

Parameters2/5

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

The schema has no descriptions for any parameters (0% coverage), so the description must explain all of them. It only describes expires_s as the validity period and its max, but says nothing about bucket or key. The description adds minimal value for only one of three parameters, insufficient to compensate for the lack of schema documentation.

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 states the action 'Generate' and the resource 'pre-signed PUT URL', which is a clear verb+resource pair. The 'PUT' clearly distinguishes it from presign_get, so an agent can tell them apart without looking at the schema.

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

Usage Guidelines2/5

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

There is no guidance on when to use this tool versus put_object or presign_get. It doesn't mention that this is for client-side uploads or that it should be used when delegating upload capability, leaving the agent to infer the use case.

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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