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video_add_text

Overlay titles, captions, or watermarks on a video by burning a single styled text element at a chosen position and time, returning the saved output path.

Instructions

Overlay text on a video (titles, captions, watermarks). Returns JSON {success, output_path}. Use to burn a single text element into a video. Pass input_path as the source video, text with the string to draw, and position/size/color to style it; output_path is auto-named when omitted.

Args: input_path: Absolute path to the input video. text: Text to overlay. position: Position on screen. Named (top-left, top-center, etc.), pixel" " {"x": 100, "y": 50}, or percentage {"x_pct": 0.5, "y_pct": 0.5}. font: Path to font file. Uses system default if omitted. size: Font size in pixels. color: Text color (CSS color name or hex). shadow: Add text shadow for readability. start_time: When the text appears (seconds). Null = always visible. duration: How long text is visible (seconds). Requires start_time. output_path: Where to save the output. Auto-generated if omitted. crf: Override CRF value (0-51, lower = better quality). Default 23. preset: Override FFmpeg encoding preset (ultrafast, fast, medium, slow, veryslow).

Input Schema

NameRequiredDescriptionDefault
crfNo
fontNo
sizeNo
textYes
colorNowhite
presetNo
shadowNo
durationNo
positionNotop-center
overwriteNoExplicitly allow replacing existing media. Existing non-media files are protected.
input_pathYes
start_timeNo
output_pathNo

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.16.4
    • addedInput schema / properties / overwrite
      Added value: +{
+  "default": false,
+  "description": "Explicitly allow replacing existing media. Existing non-media files are protected.",
+  "title": "Overwrite",
+  "type": "boolean"
+}
  2. Changed1 schema field changedv1.16.0
    • addedInput schema / additionalProperties
      Added value: +false
  3. Changed4 schema fields changedv1.5.1
    • addedInput schema / properties / crf
      Added value: +{
+  "anyOf": [
+    {
+      "type": "integer"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "title": "Crf"
+}
    • addedInput schema / properties / position / anyOf
      Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "additionalProperties": true,
+    "type": "object"
+  }
+]
    • removedInput schema / properties / position / type
      Removed value: -"string"
    • addedInput schema / properties / preset
      Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "title": "Preset"
+}
  4. First observedv0.2.0

TDQS

A3.8/5.0
Behavior3/5

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

With no annotations, the description carries the full burden, and it does disclose the return shape {success, output_path} and that output_path is auto-generated when omitted. It does not say whether the source video is modified, that the operation re-encodes (and is therefore lossy/quality-affecting), or what permissions/overwrite behavior apply beyond the crf/preset hints.

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 prose lead is three tight, front-loaded sentences covering purpose, return value, and scoping. The long Args block is justified given near-zero schema description coverage, though it slightly duplicates the lead sentence.

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

Completeness4/5

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

An output schema exists, so restating the return JSON is minor redundancy; the description fills the real gaps with per-parameter semantics and auto-naming behavior. The remaining omission is behavioral: no disclosure that rendering re-encodes the video or how overwrite interacts with existing output files.

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

Parameters5/5

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

Schema coverage is only 8% across 13 parameters, so the description must compensate and largely does: it explains position's three syntaxes (named, pixel {x,y}, percentage {x_pct,y_pct}), that duration requires start_time, that start_time null means always visible, the CRF range and quality direction, and preset values. Only overwrite is left to the schema, which already documents it.

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+resource (overlay text on video) with concrete examples (titles, captions, watermarks) and pins scope as 'a single text element', which implicitly distinguishes it from the sibling video_add_texts. It never names that sibling or other text-related tools explicitly, so differentiation is inferred rather than stated.

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?

'Use to burn a single text element into a video' hints at when this tool applies versus multi-element alternatives, but no sibling (video_add_texts, video_subtitles, video_watermark, video_text_animated) is named and no when-not guidance or prerequisites are given.

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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