AutoPoster AI

Get Direct S3 Upload URL

autoposter_get_media_upload_url

Generates a presigned S3 upload URL for direct, high-speed upload of videos or images up to 5GB without size limits or timeouts. Returns direct PUT url, POST upload fields, and public CDN URL.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`fileName`	Yes	Name of the file including extension (e.g. 'promo_video.mp4', 'photo.jpg').
`contentType`	Yes	MIME type of the media (e.g. 'video/mp4', 'image/jpeg', 'image/png').

Output Schema

TableJSON Schema

Name	Required	Description
`key`	Yes	S3 object key for the media file.
`cdnUrl`	Yes	Public CDN URL after upload.
`success`	Yes	Whether the upload URL was successfully created.
`uploadPost`	No	Presigned POST fields if using multipart upload.
`directPutUrl`	Yes	Presigned S3 PUT URL for direct upload.
`instructions`	No	Instructions for completing the direct upload.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 7, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "cdnUrl": {
+      "description": "Public CDN URL after upload.",
+      "type": "string"
+    },
+    "directPutUrl": {
+      "description": "Presigned S3 PUT URL for direct upload.",
+      "type": "string"
+    },
+    "instructions": {
+      "description": "Instructions for completing the direct upload.",
+      "type": "string"
+    },
+    "key": {
+      "description": "S3 object key for the media file.",
+      "type": "string"
+    },
+    "success": {
+      "description": "Whether the upload URL was successfully created.",
+      "type": "boolean"
+    },
+    "uploadPost": {
+      "description": "Presigned POST fields if using multipart upload.",
+      "type": "object"
+    }
+  },
+  "required": [
+    "success",
+    "key",
+    "cdnUrl",
+    "directPutUrl"
+  ],
+  "type": "object"
+}

First observedOct 7, 2026

TDQS

A3.6/5.0

Behavior4/5

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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true); the description adds meaningful context beyond them by clarifying that the tool only generates a presigned URL rather than performing the upload, and by disclosing the 5GB ceiling and the returned credential shapes. It stops short of stating URL expiration, which matters operationally for a presigned credential.

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?

Two tight, front-loaded sentences that lead with the action and then the return payload. Minor redundancy/marketing tone in 'high-speed' and the slightly self-contradictory framing 'up to 5GB without size limits' costs it the top score.

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?

An output schema exists, so the description need not explain return values, and it correctly avoids the 2 well-documented params. However, for a presigned-credential tool it omits how long the URL remains valid and does not route the agent between this and autoposter_upload_media, leaving a real operational gap.

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% and both parameters carry examples, so the schema already does the heavy lifting. The description adds no syntax, constraint, or format detail beyond what the schema provides, which is the expected baseline of 3.

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?

States a specific verb and resource: 'Generates a presigned S3 upload URL' and enumerates what it returns (PUT url, POST fields, CDN URL). It does not distinguish itself from the closely related sibling autoposter_upload_media, which an agent could easily confuse with this.

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?

Usage is only implied through the size/capability framing ('up to 5GB without size limits or timeouts'), which hints at large-file or direct-client uploads. There is no explicit when-to-use, when-not-to-use, or comparison against autoposter_upload_media, the obvious alternative.

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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