Magic Hour

by ai.magichour.mcp

Overview Discussions Admin

Auto Subtitle Generator

auto_subtitle_generator_create_video

Automatically generate subtitles for your video in multiple languages.

MCP guidance:

This starts an async video generation job and returns id plus credits_charged immediately. If the user wants the finished result, call the wait_for_video_project helper with the returned id, or poll the matching GET /v1/video-projects/{id} endpoint until status is complete, error, or canceled. Completed projects include downloads with direct URLs. The custom wait helper also returns exact_download_urls separately from expiration metadata.
For *_file_path values, prefer an existing Magic Hour file path or a file_path returned by the upload-URL endpoint after the file bytes are uploaded. Direct public media URLs may work when they are stable, fetchable, and return raw file bytes, but hotlinked URLs can fail; when in doubt, use the presigned upload flow first and pass the returned file_path.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`name`	No	Give your video a custom name for easy identification.	Auto Subtitle - dateTime
`style`	Yes	Style of the subtitle. At least one of `.style.template` or `.style.custom_config` must be provided. * If only `.style.template` is provided, default values for the template will be used. * If both are provided, the fields in `.style.custom_config` will be used to overwrite the fields in `.style.template`. * If only `.style.custom_config` is provided, then all fields in `.style.custom_config` will be used. To use custom config only, the following `custom_config` params are required: * `.style.custom_config.font` * `.style.custom_config.text_color` * `.style.custom_config.vertical_position` * `.style.custom_config.horizontal_position`
`assets`	Yes	Provide the assets for auto subtitle generator
`end_seconds`	Yes	End time of your clip (seconds). Must be greater than start_seconds.
`start_seconds`	Yes	Start time of your clip (seconds). Must be ≥ 0.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`id`	Yes	Unique ID of the video. Use it with the [Get video Project API](https://docs.magichour.ai/api-reference/video-projects/get-video-details) to fetch status and downloads.
`credits_charged`	Yes	The amount of credits deducted from your account to generate the video. If the status is not 'complete', this value is an estimate and may be adjusted upon completion based on the actual FPS of the output video. If video generation fails, credits will be refunded, and this field will be updated to include the refund.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 24, 2026

removedInput schema / properties / context

Removed value: -{
-  "description": "Explain in 15-25 words, in third person, why this tool is called and how it supports the user's goal. For analytics only. You MUST describe only the abstract purpose of the tool call. NEVER include, repeat, paraphrase, or infer personal, sensitive, or identifying information from the user request or tool results, including names, emails, phone numbers, IPs, IDs, or credentials. You MUST generalize specific entities into roles such as \"a user\", \"the customer\", or \"an account\". Example: \"Retrieving a customer's recent orders to investigate a billing issue and help support determine the appropriate resolution.\"",
-  "type": "string"
-}

Changed1 schema field changedSep 11, 2026

addedInput schema / properties / context

Added value: +{
+  "description": "Explain in 15-25 words, in third person, why this tool is called and how it supports the user's goal. For analytics only. You MUST describe only the abstract purpose of the tool call. NEVER include, repeat, paraphrase, or infer personal, sensitive, or identifying information from the user request or tool results, including names, emails, phone numbers, IPs, IDs, or credentials. You MUST generalize specific entities into roles such as \"a user\", \"the customer\", or \"an account\". Example: \"Retrieving a customer's recent orders to investigate a billing issue and help support determine the appropriate resolution.\"",
+  "type": "string"
+}

First observedSep 1, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations only declare readOnlyHint=false, destructiveHint=false, openWorldHint=true – a bare minimum. The description adds substantial value: it discloses that this is an async job returning id + credits_charged immediately, explains the polling lifecycle (complete/error/canceled), notes that completed projects include downloads with direct URLs, and warns that hotlinked URLs may fail so the presigned upload flow should be preferred. This is behavior beyond what annotations provide.

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?

Front-loaded with the purpose, then a labeled 'MCP guidance' block that is scannable. Two paragraphs are dense but each sentence carries actionable information about async workflow or file handling; no filler. Slightly long but justified by the complexity.

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

Completeness5/5

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

Despite the tool being a 5-param nested async job with no output schema for the initial call, the description covers the full lifecycle: dispatch, polling alternative, terminal statuses, download URL availability, and file-source pitfalls. Combined with the 100% schema coverage, an agent has everything needed to invoke correctly.

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 the schema already documents all 5 parameters including the nested style custom_config and assets. The description adds specific operational guidance for *_file_path values (prefer Magic Hour paths or upload-URL results; hotlinked URLs may fail) that isn't fully in the schema. Baseline 3 is appropriate given the schema's thorough 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?

States a specific verb+resource: 'Automatically generate subtitles for your video in multiple languages.' This clearly distinguishes it from siblings like ai_video_translator_create_video (translation) or lip_sync_create_video (sync), and the resource (subtitles for video) is unambiguous.

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?

The MCP guidance section clearly explains the async workflow and directs the caller to wait_for_video_project or the GET endpoint, naming the alternative explicitly. It doesn't state when NOT to use this tool versus e.g. video_translator, but the async/polling guidance is concrete and directly actionable.

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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