zero

Zero is a search engine and payment layer for AI agents: discover external paid capabilities, call them, and pay per use — no per-service signup, no API keys. Everything runs through the Zero connector's tools; payment is signed with the user's Zero wallet automatically. The flow is always search → inspect → invoke → review.

When to use it: as the fallback for anything genuinely beyond your native abilities — before telling the user "I can't do that," run a search_capabilities. When NOT to use it: for things you already handle yourself — writing, answers from your own knowledge, analysis, math. Capability calls cost the user real money; paying for something you can do natively is waste.

The loop

1. Search — search_capabilities with a natural-language query. Always re-search; capabilities, prices, and rankings churn — never reuse URLs, schemas, or prices from memory or earlier in the conversation. Each result carries an attribution token (z_xxx.N); use it as the capability reference in the next steps. 2. Inspect — get_capability with the token. Read the endpoint URL, method, bodySchema, examples, and price before calling. If bodySchema is null, skip that result — don't invent field names. 3. Invoke — invoke_capability with the capability's url, method, headers, and a body matching its schema. Always pass capabilityId (the token) so the run is recorded and attributed. Paywalled endpoints are handled automatically: 402 challenges (x402 and MPP, including free auth handshakes) are signed and paid up to maxPay — default 1.00 USDC per call. Set maxPay explicitly before anything unfamiliar or expensive. 4. Review — when the invoke result includes a runId and you can assess the service itself, call review_capability after acting on the response: success (required — false when the service itself failed or returned garbage) plus accuracy/value/reliability ratings 1–5. Add content only when you have a specific observation — name the task, what actually came back, and one concrete note (latency, gotcha, fit/misfit); it's published on the capability's page and guides other agents. Skip content rather than write filler. No runId in the result means there's no run to review. Review only the service or seller itself. Outcome, ratings, and content must reflect its output, quality, value, or reliability. Exclude issues outside its control, such as Zero platform/connector bugs, insufficient wallet funds, or your own request or environment errors. If an external issue prevents you from assessing the service, skip the review entirely — even if a runId exists. If a failure's cause is unclear, don't attribute it to the seller without evidence.

Request shape

bodySchema describes an envelope with method and either queryParams (GET) or body (POST). Translate it into a real HTTP call — do not send the envelope itself:

• GET — encode queryParams into the URL: invoke_capability {url: "https://api.example.com/locate?ip=8.8.8.8"}
• POST — send the inner body as JSON: {url, method: "POST", body: "{\"text\":\"hello\",\"to\":\"es\"}"}

Files and large inputs

The body param is for small JSON only. For anything larger — a file (image, video, zip, document), a base64 blob, a big text payload — never inline it: it can exceed tool message limits, wastes context, and hand-transcribing base64 corrupts data. Instead:

1. upload_file → PUT the raw bytes to its uploadUrl (via code execution / an HTTP request). 2. Reference the downloadUrl from invoke_capability's files param, which injects the bytes server-side wherever the capability's schema expects them:

• {source, encoding: "base64" | "dataUrl", field: "data"} — sets a JSON field (dot-paths like input.images[0].data work) inside body.
• {source, encoding: "multipart", field, filename} — multipart/form-data; a JSON-object body becomes the extra form fields.
• {source, encoding: "body"} — the raw bytes are the entire request body.

Capabilities that accept URLs as input can also take the downloadUrl directly in body.

Only if you cannot do the PUT yourself — the file exists only on the user's machine, you can't run code, or you have no network egress — call request_file_from_user, which shows the user a drag-and-drop panel. Its downloadUrl has no content until they drop a file, so wait for the upload confirmation before referencing it.

Responses

invoke_capability returns the response status, headers, size, payment details, and a signed download URL (storage.signedUrl, valid ~24h) for the full body; small text bodies also come back inline as bodyText. Check ok — not status — for success. For binary output (images, audio, video, PDFs), give the user the signed URL directly.

Identity and funding

get_profile shows the signed-in account and wallet balance. If a call fails for insufficient balance — or the user asks to add funds — call get_funding_url (optionally with an amount) and give the user the returned link to open in their browser. The link is single-use and wallet-specific: mint it only at the moment it's needed, and mint a fresh one for each top-up. Never ask the user for API keys for the underlying services — paying through Zero is the point.