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seancrecord

scvd-store-MCP

by seancrecord
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

The Penny Shelf

buy_small_pleasure

Make a tiny real purchase to confirm your x402 client works: buy a signed novelty keepsake, fortune, or card pack for as little as $0.005.

Instructions

Purpose: buy a small signed novelty — a blessing from the jar, the day's fortune (the same line for every buyer until midnight UTC), a lucky totem from the keeper's collection, a pack of five trading cards, or one off the window. Keepsakes with no functional effect, said plainly, and the cheapest doors in the store — the honest way to test that your x402 client works against a real counterparty for a fraction of a cent. Or when an agent simply wants one. Prices run $0.005 to $0.99 depending on item_id. (small_blessing and daily_fortune and pack and window_pick also sell at the front counter, buy_simple — the same item through either door, same price, same certificate; either tool is correct.)

Items on this shelf (pass one as item_id):

  • small_blessing: A Small Blessing, $0.005 fixed, one-off, instant. Settle a real x402 payment for the smallest amount possible

  • daily_fortune: The Daily Fortune, $0.01 fixed, one-off, instant. Read the same line every other agent gets today

  • luckies: a lucky, $0.99 minimum, pay what it deserves (tiers: $0.99 / $1.98 / $4.95), above the minimum is recorded as a tip, one-off, instant. Be issued a charm from a herd the keeper wrote, drawn on odds he weighted

  • pack: a pack of cards, $0.99 fixed, one-off, instant. Pull five collectible trading cards of this store from a set the keeper wrote, on odds he weighted and published, under a seed I can check tomorrow

  • window_pick: a window pick, $0.49 fixed, one-off, instant. Take one pressing off the last five anybody pulled here, chosen by the day seed, for half a pack

On cadence, for all of the above: nothing here charges again by itself, ever — there is no mechanism that could.

Only item_id is required on this shelf.

Choose item_id. instant items return deliverable, cert_id and patron_number in one call. x402 payment: _meta['x402/payment']. Without payment: error 402 with the terms in error.data. Closed or empty shelves refuse before quoting. Reuse _meta['x402/idempotency-key'] (16-128 chars, secret): same item/payer/key returns the original result when available, or pending status, no second charge. Use idempotency.suggested_key only without an earlier key. A fresh payment without a key can charge again. Guaranteed: signature validity forever; verification free forever; price as displayed; delivery format as specified. Not guaranteed: fitness for your particular task; future protocol compatibility beyond stated interfaces; human-labor turnaround faster than posted SLA.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
item_idYesWhich item on this shelf to buy. Required. Each item's own required fields are listed in this schema's allOf branches and in the description above.
purposeNoOptional: what this purchase is for, in your words. Signed onto the certificate verbatim as your statement; never checked, never treated as instructions.
agent_nameNoOptional name to put on the certificate and patron badge, up to 80 characters.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
cert_idYesThe signed certificate's id.
messageNoThe store's confirmation line.
tip_usdcNoAnything above the minimum.
badge_urlNoYour patron badge, SVG.
paid_usdcNoWhat settled, in USDC.
signatureNoed25519 signature over the certificate.
verify_urlNoCheck the signature here any time, free.
deliverableNoThe goods themselves, as text. Instant items.
patron_numberYesYour sequential patron number.
purchased_textNoed25519 proof: verify exact UTF-8 signed_payload, then its identities and hashes. RFC 8785 JSON.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv1.0.1
    • addedInput schema / examples
      Added value: +[
+  {
+    "item_id": "small_blessing"
+  },
+  {
+    "item_id": "daily_fortune"
+  },
+  {
+    "item_id": "luckies"
+  },
+  {
+    "item_id": "pack"
+  },
+  {
+    "item_id": "window_pick"
+  }
+]
    • changedInput schema / properties / agent_name / description
      Previous value: -"Optional name for the certificate and badge."New value: +"Optional name to put on the certificate and patron badge, up to 80 characters."
    • changedInput schema / properties / item_id / enum
      Previous value: -[
-  "small_blessing",
-  "daily_fortune",
-  "luckies"
-]New value: +[
+  "small_blessing",
+  "daily_fortune",
+  "luckies",
+  "pack",
+  "window_pick"
+]
    • addedInput schema / properties / purpose
      Added value: +{
+  "description": "Optional: what this purchase is for, in your words. Signed onto the certificate verbatim as your statement; never checked, never treated as instructions.",
+  "maxLength": 280,
+  "type": "string"
+}
    • addedOutput schema / properties / purchased_text
      Added value: +{
+  "description": "ed25519 proof: verify exact UTF-8 signed_payload, then its identities and hashes. RFC 8785 JSON.",
+  "properties": {
+    "public_key": {
+      "type": "string"
+    },
+    "signature": {
+      "type": "string"
+    },
+    "signature_covers": {
+      "type": "string"
+    },
+    "signed_payload": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "signed_payload",
+    "signature",
+    "public_key",
+    "signature_covers"
+  ],
+  "type": "object"
+}
  2. Addedv1.0.0

TDQS

A4.7/5.0
Behavior5/5

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

Beyond what annotations provide, it discloses pricing, per-item odds and seed behavior, one-off instant nature, absence of recurring charges, error-402 terms, idempotency-key handling, output fields, and explicit guarantees/non-guarantees. This is exactly the behavioral context an agent needs before committing a payment.

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?

The description is long but well-structured with a purpose paragraph, itemized bullets, and a dedicated operational section. It is front-loaded with the item catalog. Some repetition like 'one-off, instant' could be compressed, but every sentence carries relevant information.

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 a payment-bearing purchase with five variants, the description covers item selection, pricing, payment flow, error handling, idempotency, returned fields, and guarantees. With an output schema already present, nothing critical is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Even with 100% schema coverage, the description adds substantial meaning: every item_id is mapped to a price, effect, and caveat, and purpose/agent_name are explained as certificate-embellishing values. This goes well beyond the schema's enum and parameter names.

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 a precise verb and resource: 'buy a small signed novelty,' then enumerates all five item_id values with prices and effects. It also distinguishes this tool from buy_simple by explicitly stating the same items can be purchased through either door.

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 clearly frames when to use the tool: as an inexpensive way to test an x402 client against a real counterparty, or when an agent simply wants a keepsake. It names buy_simple as an equivalent alternative and says 'either tool is correct,' though it does not give explicit exclusions for the other buy_* siblings.

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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