bridge-agent

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observe

Reads the current screen as an accessibility tree, returning plain text with refs, roles, names, values, states, and files. Use it first to inspect browser or desktop state before acting.

Instructions

Read the current screen as one accessibility tree and return it as text.

Call this first, and again whenever you need fresh refs. The result starts with a SURFACE line:
'browser' means the tree is the web page (refs b1, b2, ...); 'desktop' means it is the native window that has
keyboard focus such as Explorer, Calculator, a Save dialog or a Windows prompt (refs d1, d2, ...). A Chrome dialog
drawn on top of the page (print preview, permission bubble) is included with d refs. Each line shows the ref, role,
accessible name, value and state of an element, followed by a visible-text excerpt and the files downloaded so far.
Nothing is clicked or changed.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`start_url`	No	Optional URL to open in the agent's browser before observing, e.g. 'https://example.com' or a file:// page. Leave empty to observe the current state.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 16, 2026

TDQS

A4.1/5.0

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 it does well: 'Nothing is clicked or changed' declares the read-only, side-effect-free profile, and it explains result structure, SURFACE semantics, ref prefixes (b/d), and embedded content like downloaded files. It omits auth constraints and any rate-limit/cost behavior, so it is strong but not exhaustive.

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?

Front-loaded with the core action, then dense but relevant detail on refs and the SURFACE line. It is on the long side and could tighten the mid-section, but each sentence conveys operational meaning rather than filler.

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?

An output schema exists so return values need not be re-explained, yet the description usefully clarifies the semantics of refs that schema alone may not convey. The main gap is the undefined boundary with navigate/launch for opening a URL via start_url, which an agent must infer.

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% and the single optional start_url is documented in the schema with a default and example. The description adds nothing about start_url and doesn't clarify its relationship to the navigate sibling, so the baseline 3 applies.

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 ('Read the current screen as one accessibility tree and return it as text') and defines the exact return shape. An agent can distinguish this observation tool from the action siblings (click, type_text, press) without opening any 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?

'Call this first, and again whenever you need fresh refs' gives clear timing guidance tied to a concrete condition. It doesn't name when not to use it or route to an alternative (e.g. navigate/launch for opening pages), so it stops short of full when/when-not/alternatives coverage.

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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