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clivejefferies

mobile-debug-mcp

wait_for_screen_change

Wait for a screen transition to complete by detecting a change from a previous fingerprint, used when navigation timing is uncertain.

Instructions

Purpose: Detect that a screen transition has occurred by waiting for the current fingerprint to differ from a previous fingerprint.

Capabilities:

  • Synchronization for uncertain navigation timing

  • Detection that something changed on screen

Constraints:

  • Does not verify correctness of the resulting state

  • Must not be used alone to confirm action success when an applicable expect_* tool exists

  • For backend/API activity without a visible UI change, pass the runtime action_type into classify_action_outcome and collect network evidence only if the result remains ambiguous

Recommended Usage:

  1. Capture or define the expected outcome

  2. Call an action tool

  3. Use wait_for_screen_change when transition timing is uncertain

  4. Follow with expect_screen when the expected destination is known

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
deviceIdNoOptional device id/udid to target
platformNoOptional platform override (android|ios)
timeoutMsNoTimeout in ms to wait for change (default 5000)
pollIntervalMsNoPolling interval in ms (default 300)
previousFingerprintYesThe fingerprint to compare against (required)
Behavior5/5

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

Discloses key behavioral traits: it only detects change, not correctness, and does not verify resulting state. Constraints are clearly listed. Without annotations, this description carries the full burden and does it well.

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?

Well-structured with sections (Purpose, Capabilities, Constraints, Recommended Usage). Front-loaded with purpose. Slightly verbose but every sentence adds value. Could be trimmed slightly.

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 purpose, capabilities, constraints, and usage workflow. No output schema exists, but behavior (wait, detect change) is clear. Could mention timeout behavior more explicitly, but overall complete.

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 100%, so baseline is 3. The description does not add significant meaning beyond the schema; it only mentions previousFingerprint as required. No extra explanation of other parameters.

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?

The description clearly states the tool's purpose: detecting screen transitions via fingerprint comparison. It distinguishes from expect_* tools but does not explicitly differentiate from sibling 'wait_for_ui_change', leaving some ambiguity.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit when-to-use and when-not-to-use guidance, including a note not to use alone when an expect_* tool exists, and alternative for backend/API activity. The 'Recommended Usage' section offers a clear workflow.

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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