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OpenAPI Specification
openapi: 3.2.0
info:
title: 2s — the (most) everything Papers API
version: '1'
summary: The (most) everything API.
description: 'The (most) everything API for AI agents: 575+ pay-per-call endpoints on one origin.'
contact:
name: 2s
url: https://2s.io
email: alley@2s.io
x-logo:
url: https://2s.io/icon-512.png
altText: 2s
x-guidance: 'Pay-per-call REST API for AI agents — hundreds of endpoints returning ground-truth data (US public records, company & legal identifiers, finance/SEC, crypto/web3, security & CVEs, medical codes, weather & geocoding, agriculture, energy, maritime, music, and more). Every endpoint is paid per call in USDC via x402 (Base or Solana) — no API key, no signup. Call any endpoint with no auth to get a 402 PaymentRequirements envelope, sign it (EIP-3009 on Base, partial SPL transfer on Solana), and retry with the PAYMENT-SIGNATURE header. Add ?trial=1 for one free real call per endpoint per hour to test before paying. To discover the right endpoint: GET https://2s.io/api/directory for the full catalog, or GET https://2s.io/api/search/endpoints?q=<natural-language task> for a ranked match. Per-call price is on each operation as x-payment-info (from $0.001). Batch up to 50 calls behind one payment via POST https://2s.io/api/batch/run.'
servers:
- url: https://2s.io
tags:
- name: Papers
paths:
/api/papers/citations:
get:
tags:
- Papers
summary: Citation graph for a scholarly work via OpenAlex
description: Citation graph for a scholarly work via OpenAlex. Pass id as a DOI (10.xxxx/…, doi.org URL) or an OpenAlex work id (W…). Returns the work's total citation count + reference count, and a paginated list of either the works that CITE it (view=citing, default — sort=recent for newest-first or sort=citations for most-cited-first) or the works it REFERENCES (view=referenced). Each listed work gives DOI, title, year, venue, authors, and its own citation count. Fresh citation data lands after any training cutoff. Complements papers.search (finding papers) with graph traversal (following citations).
operationId: papers_citations
deprecated: false
security:
- x402Payment: []
responses:
'200':
description: 'Normalized envelope: items = citing or referenced works (id, doi, title, year, venue, authors, citedByCount); total = full count for the selected view; meta.work = the queried work summary (citedByCount + referencedCount).'
content:
application/json:
schema:
type: object
required:
- data
- meta
properties:
data:
type: object
properties:
ok:
type: boolean
enum:
- true
items:
type: array
items:
type: object
properties:
id:
type: string
description: OpenAlex work id (short form, e.g. W3177828909).
doi:
type: string
nullable: true
title:
type: string
nullable: true
year:
type: number
nullable: true
publishedAt:
type: string
nullable: true
citedByCount:
type: number
nullable: true
authors:
type: array
items:
type: string
description: Author display names (first 10).
authorCount:
type: number
venue:
type: string
nullable: true
url:
type: string
nullable: true
required:
- id
- doi
- title
- year
- publishedAt
- citedByCount
- authors
- authorCount
- venue
- url
additionalProperties: false
total:
type: integer
nullable: true
description: Total matching rows upstream; null when unknown.
source:
$ref: '#/components/schemas/Source'
page:
type: object
properties:
number:
type: integer
size:
type: integer
pages:
type: integer
nullable: true
required:
- number
- size
- pages
additionalProperties: false
meta:
type: object
properties:
view:
type: string
work:
type: object
properties:
id:
type: string
doi:
type: string
nullable: true
title:
type: string
nullable: true
year:
type: number
nullable: true
citedByCount:
type: number
referencedCount:
type: number
required:
- id
- doi
- title
- year
- citedByCount
- referencedCount
additionalProperties: false
required:
- view
- work
additionalProperties: false
required:
- ok
- items
- total
- source
additionalProperties: false
meta:
$ref: '#/components/schemas/CallMeta'
'400':
$ref: '#/components/responses/BadRequest'
'402':
$ref: '#/components/responses/PaymentRequired'
'405':
$ref: '#/components/responses/MethodNotAllowed'
'500':
$ref: '#/components/responses/ServerError'
'502':
$ref: '#/components/responses/UpstreamError'
x-2s-id: papers.citations
x-2s-version: null
x-2s-price:
usd: 0.006
x-2s-accepts:
- x402
x-2s-response-shape: normalized
x-payment-info:
price:
mode: fixed
currency: USD
amount: '0.006000'
protocols:
- x402: {}
parameters:
- name: id
in: query
required: true
description: DOI or OpenAlex work id.
schema:
type: string
minLength: 4
maxLength: 500
- name: view
in: query
required: false
description: View.
schema:
type: string
enum:
- citing
- referenced
default: citing
- name: page
in: query
required: false
description: Page number (1-based) for paginated results.
schema:
type: integer
minimum: 1
maximum: 200
default: 1
- name: limit
in: query
required: false
description: Maximum number of results to return.
schema:
type: integer
minimum: 1
maximum: 50
default: 10
- name: sort
in: query
required: false
description: Field to sort results by.
schema:
type: string
enum:
- recent
- citations
default: recent
- $ref: '#/components/parameters/TrialMode'
/api/papers/search:
get:
tags:
- Papers
summary: Unified scientific literature search across arXiv
description: 'Unified scientific literature search across arXiv (preprints), PubMed (biomedical), and Semantic Scholar (cross-field, with citation counts). Returns a flat array of papers with stable schema: source, sourceId, doi, title, authors, abstract, year, publishedAt, citationCount, url, pdfUrl. Partial failures surface in the errors array rather than failing the whole call. Optional filters: since (YYYY-MM-DD), sources (subset), limit (max 20 per source).'
operationId: papers_search
deprecated: false
security:
- x402Payment: []
responses:
'200':
description: 'Normalized envelope: items = papers (flat array across arXiv + PubMed + Semantic Scholar; source, sourceId, doi, title, authors, abstract, year, citationCount, url, pdfUrl); total = count returned across sources; meta.errors = degraded sources; meta.sources/attribution describe per-source coverage.'
content:
application/json:
schema:
type: object
required:
- data
- meta
properties:
data:
type: object
properties:
ok:
type: boolean
enum:
- true
items:
type: array
items:
type: object
properties:
source:
type: string
enum:
- arxiv
- pubmed
- semantic-scholar
sourceId:
type: string
description: Source-native stable id (arXiv id, PMID, S2 paperId).
doi:
type: string
nullable: true
title:
type: string
authors:
type: array
items:
type: string
abstract:
type: string
nullable: true
year:
type: number
nullable: true
publishedAt:
type: string
nullable: true
description: ISO 8601 timestamp when the source provides a full date.
citationCount:
type: number
nullable: true
description: From Semantic Scholar; null for arXiv/PubMed results.
url:
type: string
description: Canonical URL to view the paper.
pdfUrl:
type: string
nullable: true
description: Direct PDF when available (mostly arXiv).
required:
- source
- sourceId
- doi
- title
- authors
- abstract
- year
- publishedAt
- citationCount
- url
- pdfUrl
additionalProperties: false
total:
type: integer
nullable: true
description: Total matching rows upstream; null when unknown.
source:
$ref: '#/components/schemas/Source'
meta:
type: object
properties:
query:
type: string
description: Echo of the free-text query.
sources:
type: array
items:
type: string
description: Sources actually queried (after filtering).
errors:
type: array
items:
type: object
properties:
source:
type: string
message:
type: string
required:
- source
- message
additionalProperties: false
description: Per-source failures; empty when all sources succeeded.
attribution:
type: array
items:
type: object
properties:
source:
type: string
license:
type: string
url:
type: string
required:
- source
- license
- url
additionalProperties: false
description: Per-source license + terms.
required:
- query
- sources
- errors
- attribution
additionalProperties: false
required:
- ok
- items
- total
- source
additionalProperties: false
meta:
$ref: '#/components/schemas/CallMeta'
'400':
$ref: '#/components/responses/BadRequest'
'402':
$ref: '#/components/responses/PaymentRequired'
'405':
$ref: '#/components/responses/MethodNotAllowed'
'500':
$ref: '#/components/responses/ServerError'
'502':
$ref: '#/components/responses/UpstreamError'
x-2s-id: papers.search
x-2s-version: null
x-2s-price:
usd: 0.006
x-2s-accepts:
- x402
x-2s-response-shape: normalized
x-payment-info:
price:
mode: fixed
currency: USD
amount: '0.006000'
protocols:
- x402: {}
parameters:
- name: q
in: query
required: true
description: Free-text search query.
schema:
type: string
minLength: 1
maxLength: 500
- name: limit
in: query
required: false
description: Maximum number of results to return.
schema:
type: integer
minimum: 1
maximum: 20
default: 10
- name: since
in: query
required: false
description: Since.
schema:
type: string
pattern: ^\d{4}-\d{2}-\d{2}$
- name: sources
in: query
required: false
description: Sources.
schema:
type: string
- $ref: '#/components/parameters/TrialMode'
components:
schemas:
Source:
type: object
description: 'Provenance of the data: upstream provider, source URL, and license.'
properties:
provider:
type: string
description: Upstream data provider.
url:
type: string
description: Source URL or documentation link.
license:
type: string
description: License / usage terms for the data.
CallMeta:
type: object
description: Per-call meta envelope — endpoint id, cost, caller kind, settlement details.
X402PaymentRequiredV2:
type: object
description: x402 v2 PaymentRequired envelope. Pick any entry from accepts[], sign for that rail, retry with the PAYMENT-SIGNATURE header.
required:
- x402Version
- accepts
properties:
x402Version:
type: integer
const: 2
error:
type: string
description: Human-readable reason payment is required.
resource:
type: string
description: The resource URL being purchased.
accepts:
type: array
description: Payment requirement options, one per supported network (Base USDC, Solana USDC).
items:
type: object
required:
- scheme
- network
- amount
- asset
- payTo
- maxTimeoutSeconds
properties:
scheme:
type: string
enum:
- exact
network:
type: string
description: CAIP-2 network id, e.g. "eip155:8453" (Base) or "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp".
amount:
type: string
description: Price in atomic asset units (USDC has 6 decimals).
asset:
type: string
description: Asset contract address / mint.
payTo:
type: string
description: Treasury address to pay.
maxTimeoutSeconds:
type: integer
extra:
type: object
description: 'Rail-specific extras (EVM: EIP-712 domain name/version; Solana: feePayer).'
additionalProperties: true
extensions:
type: object
description: Optional discovery metadata (e.g. bazaar input/output schemas).
additionalProperties: true
responses:
PaymentRequired:
description: Payment required. Body contains the x402 PaymentRequirements envelope with a multi-network accepts array; the per-call price is in accepts[].amount (and on the operation as x-2s-price). Sign for whichever rail you hold USDC on (EIP-3009 for Base, partial SPL transfer for Solana) and retry with the PAYMENT-SIGNATURE header (X-PAYMENT also accepted for v1 clients).
content:
application/json:
schema:
$ref: '#/components/schemas/X402PaymentRequiredV2'
UpstreamError:
description: Upstream provider error.
MethodNotAllowed:
description: Method not allowed — see `Allow` header for the supported method.
ServerError:
description: Internal server error.
BadRequest:
description: Bad request — invalid parameters.
parameters:
TrialMode:
name: trial
in: query
required: false
description: 'Try before you buy. Set to 1 for one free real call per endpoint per hour — no wallet or payment needed — to verify the endpoint before paying. Equivalent to sending the "X-2s-Trial: 1" request header. Works on every endpoint.'
schema:
type: integer
enum:
- 1
securitySchemes:
x402Payment:
type: apiKey
in: header
name: PAYMENT-SIGNATURE
description: 'x402 protocol v2: base64-encoded PaymentPayload. Call any paid endpoint without auth to receive a 402 with a multi-network PaymentRequirements envelope. Sign for either rail: EIP-3009 transferWithAuthorization (Base USDC) OR a partial SPL token transfer (Solana USDC). Retry with PAYMENT-SIGNATURE header. X-PAYMENT is also accepted for v1 buyer clients. See https://x402.org.'