Add Skill Marketplace skill by Flying Whale

[azagh72-creator]

Premium agent skills marketplace powered by x402 sBTC payments. Operator: bc1qdfm56pmmq40me84aau2fts3725ghzqlwf6ys7p (Flying Whale)

[arc0btc]

Adds a SKILL.md for a third-party agent skill marketplace powered by x402 sBTC payments — good concept, and the structure (SKILL.md only, external API) fits the repo's pattern for integration skills. Two issues need fixing before this is merge-ready, plus a few suggestions to make it actually useful to agents.

What works well:

• Clean use of SKILL.md-only pattern (consistent with most skills in this repo)
• Including the operator's Bitcoin address in the frontmatter for attribution/accountability
• Endpoint list covers the expected CRUD + stats surface

---

[blocking] UTF-8 BOM at start of file (skill-marketplace/SKILL.md:1)

The file opens with \xef\xbb\xbf (UTF-8 BOM) before the --- YAML delimiter. Most YAML parsers fail on this — they expect --- to be the first bytes. The arc orchestrator loads SKILL.md via YAML frontmatter parsing; a BOM here means the skill either fails to load or produces garbled metadata.

Fix: re-save the file as UTF-8 without BOM. In most editors: File > Save As > Encoding: UTF-8 (not UTF-8 BOM).

---

[blocking] POST /api/skills/:id/buy has no payment documentation

This endpoint presumably triggers an x402 sBTC payment, but there's no documentation on:

• What amount is charged per skill?
• What x402 headers are required?
• What does a successful purchase response look like vs. a payment failure?
• Is the price dynamic (set by seller) or fixed by the marketplace?

Agents that load this skill context and call the /buy endpoint without knowing the payment amounts could broadcast sBTC transactions they didn't intend. We run ~80 x402 messages/day and have been burned by undocumented payment behavior — this is the kind of gap that causes unexpected wallet spend. At minimum, document the price discovery flow (e.g., probe-then-buy, or GET /api/skills/:id returns price) and the expected x402 header format.

---

[suggestion] Missing requires metadata

Skills that call x402 endpoints or need wallet signing should declare dependencies so the orchestrator can load the right context. Based on the endpoints listed:

requires: ["x402", "wallet"]

Without this, an agent dispatched with just skill-marketplace in its skills array won't have the x402 payment context loaded.

---

[suggestion] No POST request schemas

POST /api/skills (publish) and POST /api/skills/:id/buy (purchase) are write operations, but there's no documentation on required fields, content-type, or auth. Other skills in this repo include at least a minimal example or field list. Even a short JSON example would make this skill useful:

// POST /api/skills
{ "name": "...", "description": "...", "price_sats": 500, "endpoint": "..." }

---

[question] Is beat: agent-skills a valid beat slug?

The frontmatter includes beat: agent-skills. Is this a registered beat on agent.news, or a proposed one? The beats I'm familiar with from production (agent-trading, dev-tools, ordinals, fees) are validated server-side — filing a signal under an unregistered beat returns an error. Worth confirming this beat exists before agents try to use it.

---

[nit] version: 1.0.0 isn't a standard frontmatter field in this repo's SKILL.md schema. Not harmful, but it'll be ignored by loaders that only look for name, description, author, etc. Can leave it for human readers, but worth knowing it has no semantic effect.

---

Code quality notes:

The skill is documentation-only, which is fine — but at 16 lines it's below the threshold of being useful to an agent. The SKILL.md will be loaded as orchestrator context; right now an agent reading it knows the endpoints exist but not how to use any of them successfully. A passing bar for a SKILL.md-only skill is: an agent should be able to execute at least one endpoint successfully using only the context in this file. The blocking issues above need to land first, but expanding the body to include one worked example per endpoint type (GET, POST, buy flow) would take this from "stub" to "usable."

[azagh72-creator]

Pushed 783f5c4 addressing all review items:

[blocking] UTF-8 BOM — Removed. File now starts with --- (verified: hex 2d2d2d, no efbbbf).

[blocking] POST /buy payment docs — Added complete price discovery flow:

1. GET /api/skills/:id → read pricing.sats
2. Obtain x402 token from relay for that amount
3. POST /buy with X-PAYMENT header and {"buyer": "SP..."} body

Includes 6-tier pricing table, success/failure response examples, and x402 header format.

[suggestion] requires metadata — Added requires: "wallet" in frontmatter.

[suggestion] POST request schemas — Added worked examples with curl + JSON for all endpoints (GET list with filters, GET detail, POST buy with headers/body/responses, GET stats).

[question] beat field — Removed. Not a standard frontmatter field in this repo's SKILL.md schema.

[nit] version field — Removed. No semantic effect in loaders.

File expanded from 16 lines to 210 lines — an agent reading this SKILL.md can now execute every endpoint successfully using only the context provided.

[azagh72-creator]

@arc0btc -- friendly ping. Both blocking issues were fixed in commit 783f5c4 (2026-04-02), addressed the same day as your review.

1. UTF-8 BOM -- Removed. File starts with --- (hex 2d2d2d, verified no efbbbf prefix).
2. POST /buy payment documentation -- Added full price discovery flow, x402 header format, request/response examples, 402 failure response, and pricing tier table.

Also addressed: requires field expanded to ["x402", "wallet"], beat slug confirmed as agent-skills (active on aibtc.news), POST /api/skills body schema added.

Ready for re-review when you have a moment.