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by io.github.popnow-ai
OverviewDiscussionsAdmin

Add sound to a video

add_sound

Make matching sound effects and ambience for a (silent) video, like footsteps, rain or a crowd. Uses site credits with OAuth or USD with an API key; the tool quotes the price. Returns an audio file; to put it on the video, call compose_video with the video as the clip and this result as sound_url.

Input Schema

NameRequiredDescriptionDefault
promptNoOptional: the sounds you want, for example: rain on a window, a cat purring. Leave empty to match what is on screen.
max_usdNoAPI key only: maximum approved USD as a decimal string with up to 9 fractional digits. Set currency to USD. Only set after the user confirms the quoted cost_usd. Never convert max_credits.
currencyNoBilling unit: USD for API keys; credits for OAuth (optional for existing OAuth clients).
no_musicNoKeep music and speech out of the result (default true).
video_urlYesThe video to add sound to: a popnow:// link from an earlier result, or a public https link.
max_creditsNoOAuth only: the most site credits the user agreed to spend on this. Only set it after the user confirmed a quoted price.
duration_secondsNoHow many seconds of sound, 1 to 30. Default 8 (match it to the video's length).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • addedInput schema / properties / currency
      Added value: +{
+  "description": "Billing unit: USD for API keys; credits for OAuth (optional for existing OAuth clients).",
+  "type": "string"
+}
    • changedInput schema / properties / max_credits / description
      Previous value: -"The most credits the user agreed to spend on this. Only set it after the user confirmed a quoted price."New value: +"OAuth only: the most site credits the user agreed to spend on this. Only set it after the user confirmed a quoted price."
    • addedInput schema / properties / max_usd
      Added value: +{
+  "description": "API key only: maximum approved USD as a decimal string with up to 9 fractional digits. Set currency to USD. Only set after the user confirms the quoted cost_usd. Never convert max_credits.",
+  "type": "string"
+}
  2. First observed

TDQS

A4/5.0
Behavior4/5

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

Annotations already declare non-read-only, open-world, non-idempotent behavior; the description adds the cost model (quoted price, user confirmation implied by using max_usd/max_credits), the credit-vs-USD auth split, and the return artifact. It doesn't discuss failure modes or whether a second call re-charges credits.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, each earning its place: what it produces, how billing works, and how to consume the result. Front-loaded with the capability, no filler or repetition of the title.

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?

Covers the capability, billing/auth branches, and output handoff to compose_video, which is what an agent needs for a 7-param paid tool with no output schema. Minor gaps remain around duration defaults and what happens on partial or failed generation.

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 every one of the 7 parameters is already documented, including the billing semantics of max_usd and max_credits. The description only reinforces billing purpose; it adds no parameter detail beyond the schema, 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?

Specific verb plus resource: 'Make matching sound effects and ambience for a (silent) video', with concrete examples (footsteps, rain, crowd). The video-input framing implicitly separates it from create_sound_effects and create_music, but no sibling is named explicitly.

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?

Gives clear operating context: it quotes a price before spending, uses credits under OAuth vs USD under an API key, and tells the agent what to do next (call compose_video with this result as sound_url). It does not state when a user should prefer create_sound_effects or create_music over this tool.

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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