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agent-bridge

agent-bridge

by avas-app
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TypeScript
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screen.capture

screen_capture

Captures a PNG screenshot of the running app and returns a file path or base64 data. Requires react-native-view-shot; otherwise it errors and you fall back to agent-device, simctl or adb.

Instructions

Screenshot the app as a PNG. Returns {path} of a file on the device. {base64:true} returns {base64} instead when small enough (else {path}). Only works if the app already has react-native-view-shot; otherwise errors and you use agent-device, simctl or adb.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "screen_capture"
  }
}

Input Schema

NameRequiredDescriptionDefault
argsNoThe tool's arguments, in order (each any JSON value). Leave out for none.
fullNoReturn a result over 32 KB whole instead of a summary of its size and shape.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv0.1.2

TDQS

A4/5.0
Behavior4/5

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

With no annotations, the description carries the full burden and does well: it discloses the return contract ({path} vs {base64}), the size-dependent branching behavior, and the failure mode plus remediation. It omits permissions/device requirements and whether capture is async, but the key behavioral traits are covered.

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?

Three tight sentences, front-loaded with purpose then return contract then failure mode; no filler. The `{path}`/`{base64}` shorthand is compact but slightly cryptic for a first-time reader.

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?

No output schema exists, so the description correctly explains return values and their size-dependent variation, plus the precondition and fallback. The tool is simple (2 params, no nesting), and what remains uncovered (e.g. the `full` flag) is fully documented in the 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 100%, so the baseline is 3, but the description adds meaning the generic 'args' array cannot convey: it documents the `{base64:true}` positional argument and its size-gated effect on the return value. The `full` parameter is left to the schema.

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?

States a specific verb and resource ('Screenshot the app as a PNG') and immediately names the return shape, so the agent knows exactly what it gets. It does not differentiate from the sibling screen_snapshot, leaving the agent to infer which snapshot-like tool to pick.

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 a hard precondition ('Only works if the app already has react-native-view-shot') and a concrete fallback path (agent-device, simctl, adb) when that fails. It stops short of stating when to prefer this over screen_snapshot, which is the one competing sibling.

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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