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twiddle-mcp

Stop your agent twiddling its thumbs. — a Twiddle Thumb Studio tool

Blocking wait_for primitives and semantic UI diffs for the iOS Simulator and Android Emulator. An MCP server that lets coding agents (Claude Code, Cursor, any MCP client) drive and — critically — verify mobile apps without screenshot → sleep → screenshot polling.

Web agents already have this: Playwright MCP's accessibility snapshots and browser_wait_for. On mobile, waiting exists only in fragments — Maestro's flow engine has implicit waits, SilbercueSwift waits on log patterns (iOS only), Appium-based stacks can script visibility waits — but no cross-platform MCP server makes blocking tree-based waits and semantic diffs the primitives agents call directly. This fills that gap.

agent: tap(ref=e4)                      → "Tapped button 'Load Data'"
agent: wait_for({text: "Welcome back"}) → blocks…
                                        → MATCHED in 1452ms:
                                          ~ text #statusLabel "Loading…" → "Welcome back, Tyler"

One tool call. No sleeps, no screenshot diffing, no wasted tokens.

Setup

// .mcp.json
{
  "mcpServers": {
    "twiddle": { "command": "npx", "args": ["-y", "@twiddlethumb/twiddle-mcp"] }
  }
}

Requirements: macOS with Xcode (iOS) and/or the Android SDK with adb on PATH. First iOS use compiles WebDriverAgent (~30s–3min, then cached). Android bootstraps in ~3s.

Related MCP server: Mobile Device MCP

Tools

Verify primitives (the point of this project):

Tool

What it does

wait_for

Block until text/element appears (or state:"gone"). Returns elapsed ms + semantic diff. On timeout returns matched:false with the current tree — never throws.

wait_for_idle

Block until the UI stops changing. Volatile elements (clocks, spinners) are auto-detected and ignored.

get_ui_tree

Accessibility tree as text with [ref=eN] markers — cheaper and more precise than a screenshot.

ui_diff

"What changed since snapshot N?" as short sentences.

handle_alert

Accept/dismiss system & in-app dialogs from the tree — handles entrance-animation frames and the tap-jacking cooldown that silently swallows an agent's too-fast taps, with verify-and-retry.

Driver: list_devices · launch_app · terminate_app · tap (by ref / selector / x,y — refs re-resolve against the live tree; a vanished element returns the current tree instead of a blind tap; scroll:true swipes through content until the selector appears, settle-aware so it never taps a still-moving list) · type_text · swipe · press_button · screenshot (fallback for purely visual checks).

How it works

Both platforms expose a localhost HTTP automation server — WebDriverAgent on iOS (bootstrapped from the appium-webdriveragent npm package), appium-uiautomator2-server on Android (APKs installed over adb). One keep-alive connection pool and one shared poll loop per device (~7Hz) serve any number of concurrent waits. Trees are normalized to a platform-agnostic node model; elements get stable refs via identity keys (role+identifier first), so refs survive re-renders; diffs align by those keys and suppress frame jitter and volatile elements.

Development

pnpm install
pnpm test        # unit tests (tree engine, wait logic) — no devices needed
pnpm build       # dist/index.js
examples/ios-demo/build.sh   # build + install the SwiftUI demo on the booted sim

Benchmark

Measured against mobile-mcp, Maestro MCP, and the raw screenshot baseline on both platforms (tap → verify a 2s async load; medians over repeated runs, canonical agent patterns, full method in bench/RESULTS.md):

agent turns

context/verification

est. total (Android / iOS)

twiddle-mcp

2

1 KB

11s / 9s

mobile-mcp

3–4 (1 poll/turn)

3 KB

16s / 14s*

maestro-mcp

1 (flow YAML)

0.3 KB

10s / 6s

screenshots + shell (default)

3

117 KB

12s / ✗ (simctl cannot tap)

* iOS requires a workaround for mobile-mcp's fractional-coordinate click bug (see RESULTS.md).

On failure (wait_for timeout), the agent gets the full current UI tree to reason over; a failed Maestro flow returns a 288-byte error string, and polling patterns return their last snapshot. Every extra second of app latency costs polling tools another turn; it costs wait_for nothing.

Status

Early but working: iOS + Android verified end-to-end over real MCP stdio (see bench/ and examples/). Roadmap: event-driven AccessibilityService transport on Android, iOS benchmark, agent-level benchmark via headless Claude Code sessions (bench/run.mjs).

MIT

Available Tools

13 tools
get_ui_treeA

Get the current accessibility tree as structured text with [ref=eN] markers usable in tap/type_text. Much cheaper and more precise than a screenshot.

ParametersJSON Schema
NameRequiredDescriptionDefault
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
filterNoDefault 'interactive'

TDQS

A4.2/5.0
Behavior4/5

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

No annotations are provided, so the description carries full burden. It implies a read-only operation ('Get') and states it is cheap, which is appropriate. However, it does not explicitly confirm no side effects or state change.

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?

Two sentences, concise and front-loaded with the essential purpose and output format. No unnecessary information.

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?

Given the simplicity of the tool (2 optional params, no output schema), the description is reasonably complete. It explains the output format and its utility. It could be more precise about the marker structure, but overall adequate.

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 baseline is 3. The description adds no additional meaning to the parameters beyond what the schema provides.

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?

The description clearly states it retrieves the accessibility tree as structured text with markers for interaction, and explicitly distinguishes it from screenshot by noting it is cheaper and more precise.

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 description provides a clear comparison to screenshot, suggesting when to prefer this tool over an alternative. However, it does not explicitly exclude other use cases or mention when not to use it.

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

handle_alertA

Accept or dismiss a blocking alert/dialog (system permission prompts, 'Open in …?' sheets, in-app modals). Finds the right button from the current UI tree — no coordinates needed. Use buttonText for a specific button. Returns what was tapped and what changed; if no alert is present you get the current tree.

ParametersJSON Schema
NameRequiredDescriptionDefault
actionNoDefault 'dismiss' (the safe choice)
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
buttonTextNoTap this specific button instead of the action vocabulary

TDQS

A4.3/5.0
Behavior4/5

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

With no annotations, the description carries the full burden. It states the tool returns what was tapped and what changed, and returns the current tree if no alert is present. It also notes no coordinates are needed, implying UI-tree-based interaction. This provides adequate transparency for agent decision-making, though it could mention any side effects or permission requirements.

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 front-loaded with essential information. First sentence covers purpose and examples, second explains mechanism, third gives usage tip and return behavior. No unnecessary words, every sentence earns its place.

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?

For a tool with 3 parameters and no output schema, the description covers return behavior, edge cases (no alert), and usage advice (buttonText). It differentiates from sibling tools effectively. The description is complete for a simple interaction tool.

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% and the schema already includes the descriptions for all three parameters (action, device, buttonText). The narrative description does not add additional meaning beyond what is in the schema, so baseline score of 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?

The description clearly states the tool accepts or dismisses blocking alerts/dialogs, with specific examples (system permission prompts, sheets, modals). It distinguishes from siblings by emphasizing 'no coordinates needed' and ability to find the right button from the UI tree.

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 description provides clear context for when to use this tool (blocking alerts) and how to use buttonText for specific buttons. It mentions default action (dismiss) and return behavior if no alert. However, it does not explicitly state when not to use it or compare with alternatives like tap or press_button.

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

launch_appB

Launch an app by iOS bundle id or Android package name.

ParametersJSON Schema
NameRequiredDescriptionDefault
appIdYesBundle id (com.example.App) or package name (com.example.app)
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
relaunchNoTerminate first if already running

TDQS

B3.1/5.0
Behavior2/5

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

With no annotations, description carries full burden. It only says 'Launch an app' with no disclosure of side effects, permission requirements, or behavior when app already running (though schema has relaunch param). Minimal behavioral context.

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?

One short sentence, very concise. However, could be slightly expanded to include key usage details while remaining efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Description does not mention necessary steps like list_devices to obtain device id, conditions for optional device, or behavior of relaunch. Lack of completeness given the tool's complexity and sibling context.

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 baseline 3. Description adds no extra meaning beyond what schema already provides for appId; device and relaunch parameters lack additional context in description.

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?

Description clearly states 'Launch an app by iOS bundle id or Android package name,' which identifies the specific verb (Launch) and resource (app) and distinguishes it from sibling tools like terminate_app or tap.

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

Usage Guidelines2/5

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

No guidance on when to use vs alternatives, prerequisites (e.g., use list_devices to get device id), or when not to use. The description only states what the tool does without context.

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

list_devicesA

List iOS simulators and Android emulators/devices. Booted devices first; use the returned id with every other tool.

ParametersJSON Schema
NameRequiredDescriptionDefault

No parameters

TDQS

A4.5/5.0
Behavior4/5

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

No annotations provided, so description carries the burden. It discloses ordering behavior and the return value's purpose. Since it's a read-only listing, no destructive hints needed.

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?

Single sentence that is concise and front-loaded with the action. No unnecessary words.

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?

Completely adequate for a parameterless listing tool. Output format is implied, and no additional context is needed given simplicity.

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?

No parameters exist, so description doesn't need to add parameter info. Baseline 4 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?

The description clearly states it lists iOS simulators and Android emulators/devices, which is a specific verb+resource. It distinguishes from sibling tools that perform actions on devices.

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?

Provides guidance on ordering (booted first) and instructs to use the returned id with other tools, indicating when to use this tool (to get device IDs). Lacks explicit when-not-to-use, but context is clear.

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

press_buttonB

Press a device button (home, back [Android], volumeUp, volumeDown, enter).

ParametersJSON Schema
NameRequiredDescriptionDefault
buttonYes
deviceNoDevice id from list_devices. Optional when exactly one device is booted.

TDQS

B3.3/5.0
Behavior2/5

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

No annotations exist, and the description does not disclose behavioral traits such as destructive effects (e.g., back may navigate away), authentication needs, or rate limits. The agent receives no safety warnings.

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?

The description is a single concise sentence that front-loads the core action and lists the buttons. No unnecessary words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple tool with 2 parameters and no output schema, the description covers the button enumeration and device optionality. However, it lacks behavioral context and usage guidance, so completeness is adequate but not thorough.

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 50%; the description adds the list of buttons (matching the enum) and explains that 'device' is optional when one device is booted. This adds marginal value beyond the schema but does not fully compensate for the missing description on other aspects.

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?

The description uses a specific verb ('press') and clearly identifies the resource ('device button'). It enumerates the exact buttons (home, back, volumeUp, volumeDown, enter), which distinguishes it from siblings like tap or swipe.

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

Usage Guidelines2/5

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

No guidance is provided on when to use this tool versus alternatives (e.g., tap for UI elements, type_text for text input). The description does not state prerequisites or when not to use it.

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

screenshotA

PNG screenshot — the fallback for purely visual checks (colors, images, layout polish). For text/structure, prefer get_ui_tree or wait_for: cheaper and more precise.

ParametersJSON Schema
NameRequiredDescriptionDefault
deviceNoDevice id from list_devices. Optional when exactly one device is booted.

TDQS

A4.2/5.0
Behavior3/5

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

No annotations are provided, so the description carries the full burden. It mentions 'PNG screenshot' implying non-destructive read-only operation, but does not disclose details like resolution, format specifics, or potential delays. Adequate but minimal.

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?

Two sentences, zero wasted words. Efficiently conveys purpose, usage guidance, and alternatives.

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?

Given the tool's simplicity (one optional parameter, no output schema, no annotations), the description is reasonably complete. It explains what it does, when to use it, and suggests alternatives. Could mention output format or typical use case more explicitly, but largely sufficient.

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?

The description adds no information beyond the schema; the schema already has 100% coverage with a clear description for the optional 'device' parameter. 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?

The description clearly states the tool produces a PNG screenshot for visual checks, specifying its use case (colors, images, layout polish) and distinguishing it from sibling tools (get_ui_tree, wait_for) that are for text/structure.

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?

The description explicitly advises using this tool for visual checks and preferring alternatives for text/structure, providing clear when-to-use and when-not-to-use guidance.

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

swipeC

Swipe in a direction (from screen center) or between explicit points.

ParametersJSON Schema
NameRequiredDescriptionDefault
toNo
fromNo
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
directionNo
durationMsNoDefault 300

TDQS

C2.4/5.0
Behavior1/5

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

No annotations are provided, and the description does not disclose behavioral traits like mutability, waiting behavior, or error handling. It merely states the action without any safety or side-effect information.

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?

Single sentence, efficient and front-loaded. However, it could benefit from a brief breakdown of the two modes for clarity.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness1/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Despite having 5 parameters including nested objects, no output schema, and no annotations, the description is too sparse. It omits details like coordinate system, duration units, and default behavior of 'from' when using 'direction'.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

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

Schema coverage is 40%, and the description adds little to parameter understanding. The 'direction' and 'from'/'to' parameters are not explained beyond their names; the default origin when using 'direction' is implied but not explicit.

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 it performs a swipe action and identifies two modes: from screen center via direction, or between explicit points. This distinguishes it from sibling tools like tap (single point) and type_text (text input).

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

Usage Guidelines2/5

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

No guidance on when to use swipe versus alternatives like tap or press_button. Prerequisites, such as device boot status or validity of coordinates, are not mentioned.

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

tapA

Tap an element by [ref=eN] from get_ui_tree/wait_for, by selector, or by x/y. Refs re-resolve against the live tree; if the element is gone you get the current tree instead of a blind tap. With scroll:true, a selector that isn't on screen is searched for by scrolling through the content first. Returns a mini-diff of what the tap changed.

ParametersJSON Schema
NameRequiredDescriptionDefault
xNo
yNo
refNo
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
scrollNoScroll to find the selector if it's not currently visible
selectorNo

TDQS

A3.9/5.0
Behavior4/5

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

With no annotations, the description fully carries the behavioral burden. It discloses that refs re-resolve against the live tree, that missing elements return the current tree instead of blind tap, that scroll:true triggers scrolling, and that the return is a mini-diff. This is thorough, though it does not explicitly cover error handling or permission requirements.

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?

The description is reasonably concise, with key information front-loaded. It uses multiple sentences but each adds value, covering targeting methods, re-resolution, scrolling, and return value. A slight reduction in redundancy could improve score.

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?

Given the complexity of the tool (multiple targeting methods, scrolling, re-resolution) and the lack of output schema, the description covers all essential behaviors and return format. It lacks only a note on prerequisites or failure states, but is otherwise 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 description coverage is low (33%), but the description explains that ref comes from get_ui_tree/wait_for and describes the selector object implicitly. However, it does not add detailed semantics for each parameter beyond what the schema already provides, leaving some parameters (x, y, ref) with minimal guidance.

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?

The description clearly specifies the action (tap), the targets (element by ref, selector, or coordinates), and distinguishes from sibling tools like press_button by listing multiple targeting methods.

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

Usage Guidelines3/5

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

The description implies when to use the tool (tapping a UI element) but does not explicitly state when to prefer it over siblings like press_button or when not to use it (e.g., when tap is not appropriate). It provides context on scrolling but lacks exclusion statements.

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

terminate_appC

Terminate a running app.

ParametersJSON Schema
NameRequiredDescriptionDefault
appIdYes
deviceNoDevice id from list_devices. Optional when exactly one device is booted.

TDQS

C2.5/5.0
Behavior2/5

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

No annotations are provided, so the description carries full burden. It only says 'terminate' without explaining side effects, gracefulness, or whether it kills the process immediately. This is insufficient for an agent to predict consequences.

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

Conciseness3/5

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

The description is very short (one sentence), which is concise but lacks structure. It could be expanded slightly without losing conciseness.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness1/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no output schema, no annotations, and a simple but critical destructive action, the description is severely incomplete. The agent is left without return value info, error handling, or prerequisite details.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

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

Schema coverage is 50% (only 'device' has a description). The description adds no extra meaning beyond the schema; it doesn't explain the role of 'appId' or provide examples. The agent must infer semantics.

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 action ('terminate') and resource ('app'), distinguishing it from sibling tools like launch_app or tap. However, it lacks specificity about which app (e.g., by appId).

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

Usage Guidelines2/5

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

No guidance on when to use this tool versus alternatives like launch_app or force-quit methods. No mention of prerequisites or contexts where termination is appropriate.

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

type_textB

Type text into the focused field (optionally tap a field first via ref/selector). submit presses Enter/Return.

ParametersJSON Schema
NameRequiredDescriptionDefault
refNoField to tap before typing
textYes
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
submitNo
selectorNo

TDQS

B3.3/5.0
Behavior3/5

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

With no annotations, the description carries the full burden of behavioral disclosure. It covers key behaviors (typing into focused field, optional tap, submit pressing Enter) but omits details such as error handling if no field is focused, whether text is appended or replaced, or the return value. This is adequate but lacks depth.

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?

Two sentences, front-loaded with the core purpose, no fluff. Every word contributes. Ideal conciseness.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (5 parameters, nested object, no output schema), the description covers the main flow but is incomplete. It does not explain what happens on focus failure, device handling (though covered in schema), or return values. Could be more thorough for a mutation tool.

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?

The description adds meaning to 'ref', 'selector', and 'submit' parameters beyond the schema, but the critical 'text' parameter remains undocumented. Since schema coverage is only 40%, the description partially compensates but leaves gaps for the most important parameter.

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 main action ('Type text into the focused field') and specifies optional field tapping and submit behavior. It is unambiguous but does not explicitly distinguish itself from sibling tools like 'tap' or 'press_button', missing the top-tier differentiation.

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

Usage Guidelines2/5

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

The description only implies usage contexts (e.g., 'optionally tap a field first') but provides no explicit guidance on when to use this tool versus alternatives like 'tap' or when not to use it. No exclusions or prerequisites are mentioned.

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

ui_diffA

Semantic diff of the current UI vs a previous snapshot (default: the last one this server took). Answers 'what changed?' without comparing screenshots.

ParametersJSON Schema
NameRequiredDescriptionDefault
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
sinceSnapshotIdNoSnapshot id to diff against (server keeps the last 5)

TDQS

A3.9/5.0
Behavior3/5

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

With no annotations provided, the description carries the full burden. It discloses that the diff is semantic and that it defaults to the last snapshot, and mentions the server keeps 5 snapshots. However, it does not describe the output format (e.g., list of changes, text), or mention idempotency, side effects, or what happens if no snapshot exists. More behavioral detail would be helpful.

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?

The description is two sentences long with no wasted words. It is front-loaded with the core purpose and provides key context in a concise manner.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no output schema, the description should hint at the return value. It says 'answers what changed' but does not specify whether the output is a structured diff, text, or list. Missing details on prerequisites (e.g., a snapshot must exist) and error handling. With sibling tools, the overall purpose is clear, but completeness is adequate but not thorough.

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?

Both parameters are documented in the schema (100% coverage), and the description adds value by specifying the default snapshot behavior ('default: the last one this server took') and the condition for device ('when exactly one device is booted'). This goes beyond the schema descriptions.

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?

The description clearly states it computes a semantic diff between the current UI and a previous snapshot, and explicitly says it answers 'what changed?' without comparing screenshots. This distinguishes it from sibling tools like screenshot and get_ui_tree, and the verb 'diff' combined with the resource 'UI' makes the purpose specific.

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

Usage Guidelines3/5

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

The description implies usage for detecting UI changes programmatically, but does not provide explicit guidance on when to use this tool versus alternatives like get_ui_tree or screenshot. There are no when-not-to-use statements or comparisons with siblings.

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

wait_forA

BLOCK until text or an element appears (or disappears with state:'gone') — use this instead of screenshot+sleep loops. Returns immediately when the condition is met, with elapsed time and a semantic diff of what changed. On timeout it returns matched:false plus the current UI tree (never throws) so you can see what IS on screen.

ParametersJSON Schema
NameRequiredDescriptionDefault
textNoSubstring to wait for anywhere on screen
stateNoDefault 'visible'
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
selectorNo
timeoutMsNoDefault 15000, max 120000

TDQS

A4.7/5.0
Behavior5/5

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

No annotations are provided, yet the description fully discloses blocking behavior, immediate return on condition met, timeout handling (returns matched:false with UI tree), and never throwing exceptions.

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?

Two sentences packed with information, front-loaded with the primary purpose, no redundant words.

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?

Despite no output schema, the description thoroughly explains return values and timeout behavior, covering all necessary context for a responsive tool.

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 high (80%), and the description adds meaning by stating that text is a substring, state defaults to 'visible', and device is optional. The selector object details are in 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?

Clearly states the tool blocks until text or element appears/disappears, distinguishing it from screenshot loops and sibling tools like wait_for_idle or screenshot.

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 recommends this tool over screenshot+sleep loops and describes behavior on timeout, but does not provide explicit when-not-to-use scenarios.

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

wait_for_idleA

BLOCK until the UI stops changing (animations/loads settled). Volatile elements like clocks and spinners marked noisy are ignored. Use after navigation before reading the screen.

ParametersJSON Schema
NameRequiredDescriptionDefault
deviceNoDevice id from list_devices. Optional when exactly one device is booted.
quietMsNoQuiet window, default 500ms
timeoutMsNoDefault 15000, max 120000

TDQS

A4/5.0
Behavior3/5

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

No annotations exist, so description must cover behavioral traits. It mentions blocking, ignoring noisy elements, and implied idleness detection. However, it does not disclose timeout behavior, error conditions, or whether the tool returns a status, leaving gaps for an agent.

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?

Two concise sentences, no redundancy, front-loaded with key action and context. Every sentence adds value.

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?

With no output schema and three optional parameters, the description adequately explains purpose and usage. Lacks detail on return value or timeout handling, but overall sufficient for a blocking utility in context.

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 covers all three parameters with descriptions (100% coverage). The description adds no extra parameter-specific details, so baseline of 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?

The description clearly states the tool blocks until UI stops changing, using strong verb 'BLOCK' and specifying the resource. It distinguishes from sibling 'wait_for' by focusing on idleness rather than a specific condition, and adds detail about ignoring noisy elements.

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 advises use after navigation before reading the screen, providing clear context. Lacks explicit exclusions or alternatives, but the guidance is direct and actionable.

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

TDQS

A3.7/5.0
Disambiguation5/5

Each tool has a distinct purpose: tapping, typing, swiping, waiting, etc. No two tools overlap in functionality.

Naming Consistency5/5

All tool names follow a consistent verb_noun snake_case pattern (e.g., wait_for, get_ui_tree). No mixing of conventions.

Tool Count5/5

13 tools is well-scoped for mobile UI testing, covering all necessary actions without excess.

Completeness4/5

Covers core workflows like launching, interacting, waiting, and inspecting UI. Minor gaps like missing explicit scroll or long press, but swipe can compensate.

Maintenance

ActivitySlowing
ResponsivenessSyncing

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