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Presence check (not an answer check)

verify_presence
Read-only

Confirm a scraped value appears on the live page, not whether it's the correct answer. Use it as a low-cost screen before full verification, or to check a value is still present.

Instructions

Presence only: confirms the value appears on the page, NOT that it is the right answer to what was asked. Never returns pass. A was-price, a different variant's price, a shipping cost, or a tax figure can all satisfy presence. Verdicts are present, fail, or unverifiable, signed, with check_type web_field_presence_v1. Use it as a cheap screen before a full check, or when you already know what the value means and only need to confirm it still appears on the page. If your decision depends on the value being the right value, call verify_web_field instead. Scope: server-rendered pages. $0.002 per check, paid in-band via x402.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesURL of the source page the claim was scraped from
askedYesWhat the scraper was asked to extract, e.g. "get the current price and stock status"
claimYesThe scraped field(s) to verify against the live page, e.g. {"price": "£51.77", "in_stock": true}

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
engineYes
reasonsYes
verdictYes
evidenceYes
signatureYes
check_typeYes
confidenceYes
verdict_idYes
Behavior5/5

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

Annotations declare readOnlyHint=true and openWorldHint=true, and the description complements them without contradiction. It discloses that the tool 'Never returns pass,' that verdicts are 'present, fail, or unverifiable, signed, with check_type web_field_presence_v1,' and that unrelated page values like a was-price or shipping cost can satisfy presence. This significantly clarifies the open-world behavior and result semantics.

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 information-dense but well organized, leading with the core distinction and then layering verdicts, use cases, alternatives, scope, and cost. Every sentence contributes decision-relevant detail without repetition or filler.

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?

Given the output schema exists and the annotations already cover safety and open-world behavior, the description covers the remaining essentials: purpose, verdict vocabulary, when to use, when not to use, alternative tool, scope, and cost. Nothing critical is missing for an agent to select and invoke this tool correctly.

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. The description adds value by scoping url to server-rendered pages and clarifying that claim is verified for appearance rather than correctness, which directly informs how to populate the parameters. This lifts it slightly above the baseline.

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 opens with 'Presence only: confirms the value appears on the page, NOT that it is the right answer to what was asked,' giving a specific verb, resource, and scope. It also explicitly names verify_web_field as the alternative for answer-level checks, making sibling differentiation immediate and unambiguous.

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 states when to use this tool ('cheap screen before a full check, or when you already know what the value means') and when not to ('If your decision depends on the value being the right value, call verify_web_field instead'). It also adds a scope constraint (server-rendered pages) and cost context, leaving no ambiguity about selection.

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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