Sponge

Sponge builds financial infrastructure for the agent economy — wallets that let AI agents hold and spend money, and a gateway that lets businesses sell services directly to agents. The Sponge Wallet API gives an agent its own multi-chain crypto wallet with balances, transfers, swaps, cross-chain bridges, payment links, cards (including a Rain-issued Visa Sponge Card), fiat onramps (Coinbase, Stripe), and trading on Hyperliquid and Polymarket, plus paid access to external services via the x402 and MPP agent-payment protocols. A TypeScript and Python SDK, a spongewallet CLI, and hosted MCP servers ship first-party. Backed by Y Combinator (W2026).

Sponge publishes 10 API contracts indexed on the APIs.io network, including Agents API, Cards API, Fiat API, and 7 more. Tagged areas include Company, Agentic Payments, AI Agents, Wallets, and Cryptocurrency.

The Sponge catalog on APIs.io includes 1 Spectral governance ruleset.

Sponge’s developer surface includes documentation, getting-started guide, support, signup flow, authentication, CLI, sandbox, and 22 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

49.2/100 developing ▬ flat Agent 51/100 agent ready Front door AI 4/6 moderate Heartbeat 51/100 slowing saas Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

1 published contract 1 MCP Servers 3 Agent Skills

Company Agentic Payments AI Agents Wallets Cryptocurrency Payments Stablecoins x402 MPP Financial Infrastructure MCP Fintech Cards On-Ramp

What this lets a business do 1

Business capabilities this provider's published APIs can perform, derived from its own contracts. Browse all capabilities →

Agent Infrastructure & Agentic Commerce

AE-100

Agents

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 49.2/100 · developing

Contract Quality 9.8 / 19

Developer Ergonomics 12.5 / 15

Access Clarity 5.1 / 15

Operational Transparency 0.3 / 10

Contract Governance 2.9 / 9

Discoverability 5.6 / 8

Regulatory Posture 4.7 / 15

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 51/100 · agent ready

Machine-Readable Contract 18 / 18

Agentic Access Contract 10 / 10

Documented Reversibility 0 / 6

MCP Server 12 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 7 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 5 / 5

Well-Known Catalog 4 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 6 / 6

Protected Resource Metadata 5 / 5

Registration Without a Human 6 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Payments regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics applies to this provider. This API accepts writes, so it carries 10 points of the composite. It is scored from the published contracts themselves: whether a caller can create-or-update in one call, whether the write accepts a key the caller already holds, and whether the response says which branch ran. Without that, every write needs a search-and-branch in front of it, and the first time that check is skipped a duplicate record is created. Scored against the observed mean rather than raw — a provider at the catalog average is unchanged by this facet, not penalised by it.

The six quality facets above are damped to 75 points between them, because the conditional facet above carries the other 25. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 75% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Rate-Limit Signaling +7 pts — OpenAPI responses document X-RateLimit-* / RateLimit headers (verified), else a rate_limits artifact or RateLimits link (documented)
Typed Event Surface +6 pts — AsyncAPI document, OR webhooks/callbacks objects in the as-published OpenAPI, OR common[].type includes Webhooks
Documented Reversibility +6 pts — a reversal operation in the contract, graded up when a window is documented too

3 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Access Clarity scores 34.2 — up to +13.2 composite points
Operational Transparency scores 2.6 — up to +12.7 composite points
Contract Quality scores 52.1 — up to +12.0 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/sponge/apis.yml: open an issue on github.com/api-evangelist/sponge to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Markets this provider is in provisional

The Kin Score Market layer reads a provider inside its market: its position, and how deep its integrations go. Depth is only comparable within a position. Provisional and unweighted: not part of the Kin Score or agent readiness.

Market	Position	Depth	Registered MCP server	Declares compatibility
Stablecoins and Tokenization (stablecoin issuers, tokenized assets)	standard	45.0	-	1
x402 Micropayments & Agentic Pay-per-Call	standard	45.0	-	1

Registered MCP server and declares compatibility are report only — not weighted. Undeclared means we found nothing we can read, so there is no number: we never infer integrations.

Standards implemented 9

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

Machine Payments Protocol (MPP)

tagged — the provider's own APIs.json carries the standard as a tag; implementation not verified

Model Context Protocol (MCP)

measured — observed by APIs.io (verified)

x402

tagged — the provider's own APIs.json carries the standard as a tag; implementation not verified

Agent Skills

measured — observed by APIs.io (published)

OAuth 2.0 Protected Resource Metadata

measured — observed by APIs.io (verified)

Dynamic Client Registration

measured — observed by APIs.io (published)

OpenAPI

measured — observed by APIs.io (published)

OAuth 2.0

measured — observed by APIs.io (declared)

OpenID Connect

measured — observed by APIs.io (declared)

APIs 10

Individual APIs this provider publishes, each with its own machine-readable definition.

Sponge Agents API

The Agents API from Sponge — 5 operation(s) for agents.

Sponge Cards API

The Cards API from Sponge — 6 operation(s) for cards.

Sponge Fiat API

The Fiat API from Sponge — 11 operation(s) for fiat.

Sponge MPP API

The MPP API from Sponge — 5 operation(s) for mpp.

Sponge Payments API

The Payments API from Sponge — 1 operation(s) for payments.

Sponge Secrets API

The Secrets API from Sponge — 2 operation(s) for secrets.

Sponge Card API

The Sponge Card API from Sponge — 7 operation(s) for sponge card.

Sponge Trading API

The Trading API from Sponge — 1 operation(s) for trading.

Sponge Transfers API

The Transfers API from Sponge — 9 operation(s) for transfers.

Sponge Wallet API

The Wallet API from Sponge — 4 operation(s) for wallet.

Scroll for all 10

Open Collections 10

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

Sponge public Agents API

OPEN COLLECTION

Sponge public Agents Cards API

OPEN COLLECTION

Sponge public Agents Fiat API

OPEN COLLECTION

Sponge public Agents MPP API

OPEN COLLECTION

Sponge public Agents Payments API

OPEN COLLECTION

Sponge public Agents Secrets API

OPEN COLLECTION

Sponge public Agents Sponge Card API

OPEN COLLECTION

Sponge public Agents Trading API

OPEN COLLECTION

Sponge public Agents Transfers API

OPEN COLLECTION

Sponge public Agents Wallet API

OPEN COLLECTION

Scroll for all 10

Arazzo Workflows 2

Multi-step API workflows described with the Arazzo specification.

Sponge — create an agent and issue its key

Platform backend creates a new agent, then mints an agent API key for runtime use.

ARAZZO

Sponge — check balance, transfer, and confirm

Read wallet balances, send an EVM transfer, then poll transaction status.

ARAZZO

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

Sponge MCP Server

Sponge publishes official, hosted (remote) MCP servers for both the agent Wallet and the merchant Gateway. Wallet servers authenticate with an agent API key (sponge_live_...) fo...

MCP SERVER

Agent Skills 3

Packaged agent skills for driving this provider's APIs from an AI assistant.

Issue and fund a Sponge Card

AGENT SKILL

Pay for a paid service with a Sponge wallet

AGENT SKILL

sponge-wallet

AGENT SKILL

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

Sponge API Rules

52 rules · 44 errors 7 warnings 1 info

SPECTRAL

OpenAPI Overlays 1

Overlays applied on top of this provider's contracts. Each card says who wrote it: a document the provider publishes, or one API Evangelist derived or generated.

Sponge Openapi Overlay

3 actions · update · sponge-openapi-original.json

DERIVED

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Sponge Authentication

http/oauth2/openIdConnect · 4 schemes

SECURITY

Sponge Domain Security

TLSv1.3

SECURITY

Scopes 1

OAuth scopes governing access to this provider's APIs.

Sponge Scopes

5 scopes

SCOPES

Agentic Access 1

Recommended x-agentic-access execution contracts for AI agents.

Sponge Agentic Access

57 operations · 31 acting

AGENTIC

Resources

Get Started 4

Portal, sign-up, and the first successful call

DeveloperPortal

GettingStarted

SignUp

Sandbox

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Agent Surfaces 5

MCP servers, agent skills, and machine-readable catalogs

AgenticAccess

MCPServer

LLMsTxt

WellKnown

AgentSkill

Design & Contract 6

Pagination, idempotency, versioning, errors, and events

Conventions

Conformance

DataModel

Lifecycle

Arazzo

Arazzo

Build 4

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

Packages

SDKs

CLI

Access & Security 3

Authentication, authorization, and security posture

Authentication

Authentication

OAuthScopes

OAuthScopes

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

Support

Support

Commercial 2

Pricing, plans, and the legal terms of use

TermsOfService

TermsOfService

PrivacyPolicy

PrivacyPolicy

Company 1

The organization behind the API

Website

Website

Other 2

Properties that don't map to a standard resource type

CapabilityMap

CapabilityMap

Overlay

Overlay

Source (apis.yml)

aid: sponge
name: Sponge
description: Sponge builds financial infrastructure for the agent economy — wallets that let AI agents hold and spend money,
  and a gateway that lets businesses sell services directly to agents. The Sponge Wallet API gives an agent its own multi-chain
  crypto wallet with balances, transfers, swaps, cross-chain bridges, payment links, cards (including a Rain-issued Visa Sponge
  Card), fiat onramps (Coinbase, Stripe), and trading on Hyperliquid and Polymarket, plus paid access to external services
  via the x402 and MPP agent-payment protocols. A TypeScript and Python SDK, a spongewallet CLI, and hosted MCP servers ship
  first-party. Backed by Y Combinator (W2026).
url: https://raw.githubusercontent.com/api-evangelist/sponge/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: true
  label: Hosted service · you call their endpoint
  confidence: high
  source:
  - openapi
  - pricing
  generated: '2026-08-28'
  method: derived
specificationVersion: '0.23'
x-backed-by:
- y-combinator
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - scopes
  - security
  - sandbox
  generated: '2026-11-06'
  method: derived
image: https://paysponge.com/logo.png
x-docs-platform: mintlify
x-docs-platform-confidence: medium
x-docs-platform-checked: 2026-10-04
tags:
- Company
- Agentic Payments
- AI Agents
- Wallets
- Cryptocurrency
- Payments
- Stablecoins
- x402
- MPP
- Financial Infrastructure
- MCP
- Fintech
- Cards
- On-Ramp
tags_raw:
- Company
- Agent Payments
- AI Agents
- Wallets
- Cryptocurrency
- Payments
- Stablecoins
- x402
- MPP
- Financial Infrastructure
- MCP
- Fintech
- Cards
- Onramp
created: '2026-07-17'
modified: '2026-09-16'
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
apis:
- aid: sponge:sponge-agents-api
  name: Sponge Agents API
  description: The Agents API from Sponge — 5 operation(s) for agents.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Agents
  properties:
  - type: OpenAPI
    url: openapi/sponge-agents-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-cards-api
  name: Sponge Cards API
  description: The Cards API from Sponge — 6 operation(s) for cards.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Cards
  properties:
  - type: OpenAPI
    url: openapi/sponge-cards-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-fiat-api
  name: Sponge Fiat API
  description: The Fiat API from Sponge — 11 operation(s) for fiat.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Fiat
  properties:
  - type: OpenAPI
    url: openapi/sponge-fiat-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-mpp-api
  name: Sponge MPP API
  description: The MPP API from Sponge — 5 operation(s) for mpp.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - MPP
  properties:
  - type: OpenAPI
    url: openapi/sponge-mpp-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-payments-api
  name: Sponge Payments API
  description: The Payments API from Sponge — 1 operation(s) for payments.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Payments
  properties:
  - type: OpenAPI
    url: openapi/sponge-payments-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-secrets-api
  name: Sponge Secrets API
  description: The Secrets API from Sponge — 2 operation(s) for secrets.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Secrets
  properties:
  - type: OpenAPI
    url: openapi/sponge-secrets-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-sponge-card-api
  name: Sponge Card API
  description: The Sponge Card API from Sponge — 7 operation(s) for sponge card.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Sponge Card
  properties:
  - type: OpenAPI
    url: openapi/sponge-sponge-card-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-trading-api
  name: Sponge Trading API
  description: The Trading API from Sponge — 1 operation(s) for trading.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Trading
  properties:
  - type: OpenAPI
    url: openapi/sponge-trading-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-transfers-api
  name: Sponge Transfers API
  description: The Transfers API from Sponge — 9 operation(s) for transfers.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Transfers
  properties:
  - type: OpenAPI
    url: openapi/sponge-transfers-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
- aid: sponge:sponge-wallet-api
  name: Sponge Wallet API
  description: The Wallet API from Sponge — 4 operation(s) for wallet.
  humanURL: https://docs.paysponge.com
  baseURL: https://api.wallet.paysponge.com
  tags:
  - Wallets
  tags_raw:
  - Wallet
  properties:
  - type: OpenAPI
    url: openapi/sponge-wallet-api-openapi.yml
  - type: APIReference
    url: https://docs.paysponge.com/api-reference/public-openapi.json
common:
- type: CapabilityMap
  url: capabilities/sponge-capability-edges.yml
  name: Sponge Business Capability Map
- type: Overlay
  url: overlays/sponge-openapi-overlay.yaml
- type: Website
  url: https://paysponge.com
- type: DeveloperPortal
  url: https://docs.paysponge.com
- type: Documentation
  url: https://docs.paysponge.com
- type: GettingStarted
  url: https://docs.paysponge.com/wallet/sdk.md
- type: Support
  url: https://discord.gg/gwH2QqMDaX
- type: GitHubOrganization
  url: https://github.com/paysponge
- type: SignUp
  url: https://wallet.paysponge.com
- type: TermsOfService
  url: https://paysponge.com/terms
- type: PrivacyPolicy
  url: https://paysponge.com/privacy
- type: Authentication
  url: authentication/sponge-authentication.yml
- type: OAuthScopes
  url: scopes/sponge-scopes.yml
- type: DomainSecurity
  url: security/sponge-domain-security.yml
- type: AgenticAccess
  url: agentic-access/sponge-agentic-access.yml
- type: MCPServer
  url: mcp/sponge-mcp.yml
- type: LLMsTxt
  url: llms/sponge-llms.txt
- type: Packages
  url: packages/sponge-packages.yml
- type: SDKs
  url: packages/sponge-packages.yml
- type: CLI
  url: cli/sponge-cli.yml
- type: WellKnown
  url: well-known/sponge-well-known.yml
- type: Conventions
  url: conventions/sponge-conventions.yml
- type: Conformance
  url: conformance/sponge-conformance.yml
- type: DataModel
  url: data-model/sponge-data-model.yml
- type: Lifecycle
  url: lifecycle/sponge-lifecycle.yml
- type: Sandbox
  url: sandbox/sponge-sandbox.yml
- type: AgentSkill
  url: skills/_index.yml
- type: Arazzo
  name: Check balance, transfer, and confirm
  url: arazzo/sponge-transfer-and-confirm.yml
- type: Arazzo
  name: Create an agent and issue its key
  url: arazzo/sponge-agent-onboarding.yml
x-enrichment:
  date: '2026-07-21'
  status: enriched
  artifacts_added: 21
  pass: local-v1

Sponge API — frequently asked questions

Does Sponge have an API?

Yes. APIs.io lists 10 APIs from Sponge, including Sponge Agents API, Sponge Cards API and Sponge Fiat API, and 7 more.

Is there an OpenAPI specification for the Sponge API?

Yes. APIs.io indexes 10 OpenAPI specifications for Sponge, each linked for download from this page.

How do I authenticate with the Sponge API?

Sponge documents its authentication (http/oauth2/openIdConnect · 4 schemes). The details are profiled on APIs.io as Sponge Authentication.

Does Sponge have an MCP server?

Yes. APIs.io lists 1 MCP server for Sponge: Sponge publishes official, hosted (remote) MCP servers for both the agent Wallet and the merchant Gateway. Wallet servers authenticate with an agent API key (sponge_live_...) for CLI clients, or OAuth

Is the Sponge API ready for AI agents?

Sponge has a Kin Score of 49.2 out of 100 (developing) and an Agent Readiness score of 51.1 (agent-ready), scored by API Evangelist on 2026-11-06.

Work with this as data

Every provider here is available over the APIs.io API and to AI agents over MCP.

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https://apis.io/mcp

Tools for providers

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find_providersBrowse and filter every provider in the catalog.
get_provider_artifactsEvery artifact this provider publishes, grouped by type.
get_provider_operationsEvery operation across all of their OpenAPIs — one call instead of parsing every spec.
get_provider_toolsEvery MCP tool they ship, with the operation each wraps.
get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
get_provider_ratingPRO — composite, band, trend and facet scores.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

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