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karbassi

slack-mcp

by karbassi

files_get_upload_url_external

Obtain a URL to upload an external file to Slack. Specify file name and size to get a secure upload link.

Instructions

Get an upload URL for an external file.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
filenameYes
lengthYes
alt_txtNo
snippet_typeNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Behavior2/5

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

With no annotations, the description must disclose behavioral traits, but it only states the basic function. It does not mention authentication requirements, URL expiration, file size limits, or side effects. The word 'Get' implies a read-only operation, but the full flow involves writing to an external URL, which is not discussed.

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, clear sentence with no wasted words. It is concise, though it may be too terse for the complexity of the operation. Front-loading the core purpose is good.

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 that an output schema exists, the description need not detail return values. However, the tool is part of a multi-step external file upload process, and the description fails to mention steps like uploading to the returned URL and calling files_complete_upload_external. This lack of context could lead to incorrect usage.

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

Parameters1/5

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

Schema description coverage is 0%, and the description adds no meaning to parameters. For example, 'length' likely indicates file size in bytes, but neither the schema nor the description explains this. Other parameters like 'alt_txt' and 'snippet_type' have no context. The agent cannot infer correct usage from the description alone.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description 'Get an upload URL for an external file' clearly states the action (get) and the resource (upload URL for external file). It distinguishes from sibling tools like files_upload, which actually upload content, but does not explicitly contrast with files_complete_upload_external.

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?

No guidance on when to use this tool versus alternatives such as files_upload, files_upload_v2, or files_complete_upload_external. The description omits the typical workflow of first getting a URL, uploading content to that URL, and then completing the upload with a separate call.

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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