Magic Hour

Auto Subtitle Generator

auto_subtitle_generator_create_video

MCP guidance:

Starts an async video job; returns id and credits_charged. For finished results, call wait_for_video_project with that id or poll GET /v1/video-projects/{id} until complete, error, or canceled. Results include downloads; wait helpers add exact_download_urls. Preserve signed URLs and query parameters; never append expiration metadata.
For *_file_path, use an existing Magic Hour path or the upload-URL endpoint's file_path after uploading raw bytes to its presigned URL. Direct public media URLs may work if stable and fetchable as raw bytes; hotlinked URLs can fail. Prefer the upload-URL endpoint when unsure.

Automatically generate subtitles for your video in multiple languages.

Input 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

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.

Changed2 schema fields changedOct 12, 2026
- changedInput schema / properties / end_seconds / example
```
Previous value: -15New value: +5
```
- addedInput schema / properties / style / properties / template / example
```
Added value: +"karaoke"
```

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

A4.6/5.0

Behavior5/5

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

Beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true), the description discloses a lot: async job semantics, the exact returned fields (id, credits_charged), terminal states, that wait helpers add exact_download_urls, and a preservation warning about signed URLs and expiration metadata. This is substantive behavioral context the annotations do not carry.

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?

Every sentence carries information with no filler, but the structure is inverted: the reader meets protocol guidance before the actual purpose, which lands in the final sentence. Front-loading the purpose would improve scannability.

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?

An output schema exists, yet the description still usefully covers the async lifecycle, terminal statuses, and returned identifiers, and it fully addresses the tricky asset-input path for a nested-object, 5-param tool. Nothing needed to invoke it correctly is missing.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3, but the description adds real value by explaining how to obtain the assets.video_file_path value (existing Magic Hour path vs upload-URL file_path) and warning that hotlinked public URLs can fail. It adds meaning beyond the schema's field-level descriptions.

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 names a specific verb and resource ('Automatically generate subtitles for your video in multiple languages') and clarifies the execution model ('Starts an async video job'). An agent can distinguish this from the many other create_video siblings by its subtitle-generation scope without opening 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 Guidelines4/5

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

It clearly explains the follow-up workflow (call wait_for_video_project or poll the endpoint until complete/error/canceled) and gives routing guidance for file paths (prefer the upload-URL endpoint when unsure). It stops short of stating when NOT to use this tool versus sibling video tools, but the context for correct invocation is strong.

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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