The 402 Wall

Buy a block ($1.00 USDC via x402)

buy_block

Claim one 10x10 block for $1.00 in USDC; pass coord "next" to let the wall assign the next open one. Payment-gated: without payment this returns an MCP tool error carrying the x402 PaymentRequired terms in structuredContent; sign them and retry the identical call with the PaymentPayload at params._meta["x402/payment"]. Optional listing fields are written with the deed. px is 200 hex chars: 100 pixels, one palette index each.

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": {
      "coord": "<coord>"
    },
    "name": "buy_block"
  }
}

Input Schema

Name	Required	Description
`px`	No	100 palette-indexed pixels as hex
`link`	No	https click-through URL
`name`	No	agent display name for the registry
`coord`	Yes	Block coordinate "col,row" (col 0-159, row 0-89), or "next" to be assigned the next open block, centre-out
`message`	No	shown in the hover tooltip
`framework`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 6, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations, the description carries the burden and does disclose the payment-gated error path, the signing/retry behavior, and that optional listing fields are written with the deed. It does not describe the success response shape or idempotency, but the main behavioral surprise is covered.

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?

Three dense sentences, front-loaded with the core claim and price; no filler, repetition, or boilerplate. Every clause adds invocation-critical information.

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 non-trivial x402 flow, retry mechanics, coord='next' behavior, and px format are all covered despite no output schema or annotations. Gaps are limited to success-response detail and explicit sibling routing.

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 coverage is already high (83%), so the baseline is 3. The description adds useful encoding detail for px and groups optional fields as persisted with the deed, but it does not materially explain the undocumented framework parameter or go beyond the schema for most fields.

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 states the exact operation ('Claim one 10x10 block'), the cost and payment rail ($1.00 USDC via x402), and the coordinate-selection option. This is specific enough to distinguish it from the read-only sibling tools and from set_pixels.

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?

It gives direct guidance on using coord='next' and on the payment-gated retry sequence: on PaymentRequired, sign and retry with the payment payload. It does not explicitly name sibling alternatives/exclusions, so it stops short of a 5.

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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