veilbrowser

veil_wait_for

Poll a JavaScript expression in the page until it becomes truthy, replacing fixed sleep intervals. Returns when the condition holds; errors on timeout.

Instructions

Poll a JS expression in the page until it is truthy, instead of a fixed sleep — e.g. "document.querySelector('.results')". Returns when the condition holds; errors on timeout.

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": {
      "expression": "<expression>"
    },
    "name": "veil_wait_for"
  }
}

Input Schema

Name	Required	Description
`poll`	No	ms between checks (default 100)
`timeout`	No	ms before giving up (default 10000)
`expression`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.5.0Jul 29, 2026

TDQS

A4.6/5.0

Behavior5/5

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

With no annotations, the description fully carries the burden. It clearly states that the tool polls repeatedly, returns when the condition holds, and errors on timeout. This discloses the core behavioral traits without contradictions.

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, front-loaded with the core action, and every word earns its place. It is efficient and to the point.

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?

The description covers purpose, behavior, and main parameter with an example. It is mostly complete but could mention what the function returns (implicitly true or the result). Still, given the simplicity and presence of sibling tools, it is adequately comprehensive.

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 67% (poll and timeout described). The description adds meaning by explaining the 'expression' parameter with an example, compensating for the missing schema description. It does not add new info for already-described parameters.

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 that the tool polls a JS expression until it is truthy, providing a specific verb and resource. It distinguishes from a fixed sleep and, by implication, from sibling tool 'veil_wait_for_selector' which uses a CSS selector instead of an arbitrary expression.

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 explicitly contrasts with 'a fixed sleep', giving a clear context for when to use this tool instead. However, it does not mention when not to use it or directly compare with the selector-based wait tool among siblings.

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