BCD — Bridge Control Delegate

app_focus

Put the keyboard focus in a text field of the latest app_snapshot without changing its text. Returns the app's new state with the next snapshotId, so no extra snapshot is needed. If the window changed, or a person used the keyboard or mouse in the app since the snapshot, nothing is done and the error comes with the current state to retry from. A sent action is not proof the task succeeded. Needs ui and process permission (operating apps can run programs).

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": {
      "snapshotId": "<snapshotId>",
      "elementId": "<elementId>"
    },
    "name": "app_focus"
  }
}

Input Schema

Name	Required	Description
`deviceId`	No	Computer name or id from list_devices. Optional with one computer online or a default set.
`takeOver`	No	Only when the user says so: act even though another conversation is operating this screen, which then holds it no longer.
`elementId`	Yes
`snapshotId`	Yes
`workSessionId`	No	Work session from create_work_session. Pass the same ID on every call in this conversation; omit for legacy unscoped work.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 23, 2026

addedInput schema / properties / takeOver

Added value: +{
+  "description": "Only when the user says so: act even though another conversation is operating this screen, which then holds it no longer.",
+  "type": "boolean"
+}

AddedOct 8, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations only declare it's a non-destructive write; the description adds substantial context beyond them: the return includes the next snapshotId so no extra snapshot is needed, staleness detection aborts the action and returns current state for retry, and it flags the ui/process permission requirement plus the caveat that a sent action isn't proof of success.

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?

Four sentences, each carrying distinct information, with the core action front-loaded. The final permission sentence is a bit tacked-on and the error-path sentence is dense, but nothing is wasted.

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?

With no output schema, the description covers the return value itself, the failure/staleness path, and the permission prerequisites, and the remaining parameters are covered by schema descriptions. An agent has enough to call this correctly and interpret results.

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 coverage is 60%, with deviceId, takeOver and workSessionId already documented in the schema. The description gives useful context for snapshotId ('latest app_snapshot') but does not explain elementId's meaning or how element IDs are obtained. Baseline 3 given partial schema coverage and only marginal added detail.

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 ('put the keyboard focus') and resource ('a text field of the latest app_snapshot') and explicitly contrasts with the sibling that types into the field ('without changing its text'). An agent can distinguish this from app_type and app_select without opening either 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?

The 'without changing its text' clause implies when to choose this over app_type, and the staleness paragraph explains the retry condition explicitly. It stops short of naming the alternative tool directly or listing exclusions, so it's clear context rather than a full routing rule.

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

All BCD — Bridge Control Delegate tools Inspect

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