Agent Toolbox

Watch Field

watch_field

Watch one field on a web page for 30 days, e.g. a price, stock status or version number: it is read again every 15 to 1440 minutes and an alert goes to your webhook, Slack, Discord or Telegram when it changes, goes below or above a number, contains a text, or disappears. Returns the current value now; check status or stop it for free with the watch secret. Costs USD 0.10 per call, paid with x402 (USDC on Base); calls that fail are not charged.

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": {
      "url": "<url>",
      "field": "<field>"
    },
    "name": "watch_field"
  }
}

Input Schema

Name	Required	Description
`url`	Yes	A public http(s) URL
`type`	No	The field's type (number for below and above)
`when`	No	Default changes; below and above compare numbers; contains looks for text in the value; gone fires when the field is no longer on the page
`field`	Yes	A short name for the field, e.g. price
`label`	No	Optional name for your own reference
`value`	No	The number for below/above, or the text for contains
`format`	No	Detected from the callback host when left out
`description`	No	What the field is, e.g. the current price of the product
`callback_url`	No	Optional https URL for alerts (a signed JSON POST); Slack and Discord incoming webhooks and https://api.telegram.org/bot<token>/sendMessage?chat_id=<id> get a readable message. Without it, poll the status.
`every_minutes`	No	How often the page is read (default 60)

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 25, 2026

TDQS

A4.3/5.0

Behavior5/5

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

Adds substantial context beyond the annotations: a 30-day lifetime, a 15–1440 minute polling cadence, alert delivery to webhook/Slack/Discord/Telegram, and — critically — the cost model ($0.10 per call, USDC on Base via x402, failures not charged). The pricing disclosure also effectively warns an agent not to call repeatedly, compensating for idempotentHint=false.

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?

Two sentences, front-loaded with what is watched and how often, followed by delivery channels and price. Nearly every clause carries information, though the colon-chained enumeration makes it dense and slightly hard to scan.

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?

For a 10-parameter mutating tool with no output schema, the description covers duration, cadence, alert routing, cost, payment, and free lifecycle operations. The only gap is that it does not say the response returns a watch secret or that each call creates a separate billable watch, both of which matter for correct use.

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 every parameter is already documented, establishing a baseline of 3. The description corroborates the enum semantics indirectly by listing alert channels and condition types, but adds no syntax or formatting detail the schema does not already carry.

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 ('Watch one field on a web page for 30 days') and immediately gives concrete examples (price, stock status, version number). The 30-day lifetime and 'returns the current value now' clearly separate it from one-off reads like read_url and from the sibling stop_watch/watch_status lifecycle tools.

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 alert conditions (changes, below/above, contains, gone) and the polling interval range make it obvious when this tool is the right choice. It also tells the agent that status checks and stopping are free via the watch secret, steering follow-up calls. It never names the actual siblings (stop_watch, watch_status) nor says 'use read_url for a single read', so routing is implied rather than explicit.

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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