OpenScreen

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setVocabulary

Sets the project's Whisper vocabulary list so transcription spells names and technical terms correctly. An empty string clears it; re-transcribe assets to apply changes to existing transcripts.

Instructions

Set the project's vocabulary: the names and technical terms Whisper is primed with on every transcription of this project, so it spells them right (at most 600 characters, read as a plain list such as "OpenScreen, Vulkan, whisper.cpp"). An empty string clears it. It changes no existing transcript: transcribe the asset again for that. getCurrentDocument reports it as vocabulary.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "vocabulary": "<vocabulary>"
    },
    "name": "setVocabulary"
  }
}

Input Schema

Name	Required	Description	Default
`projectId`	No	The project to act on, from listProjects. Omit it only for the project open in the OpenScreen editor, which works only while the app runs.
`vocabulary`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.1.1Oct 18, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations mark this as a non-destructive mutation (readOnlyHint=false, destructiveHint=false), so the safety profile is covered. The description adds real behavioral context: the 600-character cap, that empty string clears it, and that it does not retroactively change transcripts. Auth/permission behavior is not mentioned, keeping it short of a 5.

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 core action and effect, followed by constraint and clearing semantics. Dense but each sentence carries a distinct fact; the final cross-reference to getCurrentDocument is a useful pointer rather than filler.

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?

For a mutation tool with no output schema, the definition covers the actionable facts: format, limit, clearing behavior, and non-retroactivity. It leaves only permission/auth details and response shape unstated, which are minor given the annotations and lack of an output schema.

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 only 50% (projectId documented, vocabulary bare), so the description must compensate, and it does: it explains that vocabulary is read as a plain list, gives an example ("OpenScreen, Vulkan, whisper.cpp"), and states the 600-char limit and empty-string semantics. projectId semantics are already carried by the schema.

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 (set) and resource (project vocabulary) plus the exact effect: what Whisper is primed with on every transcription of this project. An agent can distinguish this from getCurrentDocument and transcribe at a glance.

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?

Explicitly tells the agent that an empty string clears the vocabulary and that existing transcripts are unaffected, directing it to re-run transcribe for that. It names the relevant siblings (transcribe, getCurrentDocument) but does not spell out when to prefer this over alternatives or any prerequisites.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.