BCD — Bridge Control Delegate

app_select

Select a row, tab or list item of the latest app_snapshot; selecting a row usually opens it (an email, a file). 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_select"
  }
}

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?

Goes well beyond the annotations by disclosing side effects (selection may open a file/email), a stale-snapshot guard that no-ops and returns current state on conflict, that the response includes the next snapshotId, permission requirements (ui and process), and the caveat that sending an action isn't proof of success. This is exactly the mutation/risk context annotations don't 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?

Purpose is front-loaded, then behavior, then caveats, in a logical order with little waste. It is dense but each sentence adds use (side effects, guard, permissions, verification), though the density slightly hurts 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?

With no output schema and open-world mutations, the description still explains the return value (new app state with next snapshotId), the error path with current state for retry, and permission needs. Nothing an agent needs 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.

Parameters3/5

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

Schema coverage is 60%; deviceId, takeOver, and workSessionId are well documented in the schema itself. elementId and snapshotId have no schema description, and the description only loosely compensates by tying snapshotId to 'the latest app_snapshot' — it says nothing about elementId's valid range or selection semantics. Baseline 3 is appropriate.

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 and resource ('Select a row, tab or list item') plus the scope ('of the latest app_snapshot'), and adds the typical consequence (a row usually opens). It distinguishes clearly from siblings like app_press and app_snapshot without needing 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?

Gives concrete preconditions: must act on the latest snapshot, and outlines the failure mode when the window changed or a human intervened. It doesn't explicitly route to alternatives such as app_press for non-selectable elements, so it falls short of 5.

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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