Ressl

Ressl (ressl.ai) is a Y Combinator-backed platform that provisions hosted mock SaaS APIs for AI agents and evaluations. Its control-plane API lets you list the mock providers your organization is granted (for example jira, salesforce, slack, plus UI clones of Gmail Business and LinkedIn) and create a short-lived snapshot of one provider that returns a public HTTPS base URL your agent can call - no real customer tenant required. Snapshots carry deterministic or seeded synthetic data and expire on a TTL (default one hour, up to seven days). Control traffic runs on simulation.ressl.ai; provisioned mock traffic is served from *.mock.ressl.cc. Ressl helps teams train, benchmark, and deploy autonomous agents by giving them realistic SaaS surfaces to act against safely.

Ressl publishes 2 APIs on the APIs.io network: Providers API and Snapshots API. Tagged areas include Mock APIs, API Testing, AI Agents, Agent Evaluation, and Sandbox.

Ressl’s developer surface includes authentication, documentation, API reference, getting-started guide, signup flow, support, and 16 more developer resources.

🌐 Visit website 📡 Source on GitHub

26.5/100 thin ▬ flat Agent 30/100 agent ready saas Full breakdown ↓
scored 2026-09-08 · rubric v0.20.0

1 APIs

Mock APIsAPI Testing AI Agents Agent Evaluation Sandbox Developer Tools Synthetic Data Software-as-a-Service

Kin Score

Kin Score How this is scored →
scored 2026-09-08 · rubric v0.20.0

Composite quality — 26.5/100 · thin

Contract Quality 3.4 / 23

Developer Ergonomics 11.1 / 18

Access Clarity 2.4 / 18

Operational Transparency 0.3 / 12

Contract Governance 0.5 / 11

Discoverability 6.8 / 9

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 30/100 · agent ready

Machine-Readable Contract 18 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 8 / 8

Request/Response Examples 7 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 5 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

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.

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 github.com/api-evangelist/ressl-ai: open an issue to ask a question, or submit a pull request to add artifacts. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

APIs 2

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

Ressl Providers API

Discover mock SaaS providers granted to your organization

Ressl Snapshots API

Provision short-lived hosted mock SaaS APIs

Open Collections 3

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

API Collection

OPEN COLLECTION

Ressl Platform Providers API

OPEN COLLECTION

Ressl Platform Providers Snapshots API

OPEN COLLECTION

Security Posture 2

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

Ressl Ai Authentication

apiKey/http · 2 schemes

SECURITY

Ressl Ai Domain Security

TLSv1.3 · HSTS · DNSSEC · DMARC

SECURITY

Resources

Get Started 3

Portal, sign-up, and the first successful call

GettingStarted

GettingStarted

DeveloperPortal

DeveloperPortal

SignUp

SignUp

Documentation 3

Reference material describing how the API behaves

OpenAPI

OpenAPI

Documentation

Documentation

APIReference

APIReference

Agent Surfaces 4

MCP servers, agent skills, and machine-readable catalogs

WellKnown

WellKnown

X-MCPServerCandidate

X-MCPServerCandidate

AgentSkill

AgentSkill

LLMsTxt

LLMsTxt

Design & Contract 5

Pagination, idempotency, versioning, errors, and events

ErrorCatalog

Conventions

Lifecycle

Conformance

DataModel

Build 1

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

GitHubOrganization

Access & Security 2

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Authentication

Authentication

Operate 1

Status, limits, changes, and where to get help

Support

Support

Company 2

The organization behind the API

Website

Website

LinkedIn

Other 1

Properties that don't map to a standard resource type

Overlay

Overlay

Source (apis.yml)

aid: ressl-ai
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
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - security
  generated: '2026-09-03'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/ressl-ai.png
name: Ressl
description: Ressl (ressl.ai) is a Y Combinator-backed platform that provisions hosted mock SaaS APIs for AI agents and evaluations.
  Its control-plane API lets you list the mock providers your organization is granted (for example jira, salesforce, slack,
  plus UI clones of Gmail Business and LinkedIn) and create a short-lived snapshot of one provider that returns a public HTTPS
  base URL your agent can call - no real customer tenant required. Snapshots carry deterministic or seeded synthetic data
  and expire on a TTL (default one hour, up to seven days). Control traffic runs on simulation.ressl.ai; provisioned mock
  traffic is served from *.mock.ressl.cc. Ressl helps teams train, benchmark, and deploy autonomous agents by giving them
  realistic SaaS surfaces to act against safely.
url: https://raw.githubusercontent.com/api-evangelist/ressl-ai/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- y-combinator
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-07-20'
x-enrichment:
  date: '2026-07-20'
  status: enriched
  artifacts_added: 13
  pass: local-v1
tags:
- Mock APIs
- API Testing
- AI Agents
- Agent Evaluation
- Sandbox
- Developer Tools
- Synthetic Data
- Software-as-a-Service
tags_raw:
- Mock APIs
- API Testing
- AI Agents
- Agent Evaluation
- Sandbox
- Developer Tools
- Synthetic Data
- SaaS
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
apis:
- aid: ressl-ai:ressl-ai-providers-api
  name: Ressl Providers API
  description: Discover mock SaaS providers granted to your organization
  humanURL: https://docs.ressl.ai
  baseURL: https://simulation.ressl.ai
  tags:
  - Providers
  properties:
  - type: OpenAPI
    url: openapi/ressl-ai-providers-api-openapi.yml
  - type: Documentation
    url: https://docs.ressl.ai
  - type: APIReference
    url: https://docs.ressl.ai/api-reference/authentication
  - type: Quickstart
    url: https://docs.ressl.ai/quickstart
- aid: ressl-ai:ressl-ai-snapshots-api
  name: Ressl Snapshots API
  description: Provision short-lived hosted mock SaaS APIs
  humanURL: https://docs.ressl.ai
  baseURL: https://simulation.ressl.ai
  tags:
  - Snapshots
  properties:
  - type: OpenAPI
    url: openapi/ressl-ai-snapshots-api-openapi.yml
  - type: Documentation
    url: https://docs.ressl.ai
  - type: APIReference
    url: https://docs.ressl.ai/api-reference/authentication
  - type: Quickstart
    url: https://docs.ressl.ai/quickstart
common:
- type: Website
  url: https://www.ressl.ai/
- type: DomainSecurity
  url: security/ressl-ai-domain-security.yml
- type: Authentication
  url: authentication/ressl-ai-authentication.yml
- type: OpenAPI
  url: openapi/_original/ressl-ai-platform-openapi.yml
- type: Overlay
  url: overlays/ressl-ai-platform-overlay.yaml
- type: ErrorCatalog
  url: errors/ressl-ai-problem-types.yml
- type: Conventions
  url: conventions/ressl-ai-conventions.yml
- type: Lifecycle
  url: lifecycle/ressl-ai-lifecycle.yml
- type: Conformance
  url: conformance/ressl-ai-conformance.yml
- type: DataModel
  url: data-model/ressl-ai-data-model.yml
- type: WellKnown
  url: well-known/ressl-ai-well-known.yml
- type: X-MCPServerCandidate
  url: mcp/ressl-ai-mcp.yml
  note: 'Renamed from MCPServer 2026-09-03 (roadmap#247): the manifest self-describes as status: candidate — a tool list derived
    from the published API contracts, not an existing server. The scorer already read the manifest and reported mcp_server
    correctly; the MCPServer type was crediting the artifact-type surfaces with a server that does not exist.'
- type: AgentSkill
  url: skills/ressl-ai-skill.md
- type: LLMsTxt
  url: llms/ressl-ai-llms.txt
- type: Documentation
  url: https://docs.ressl.ai
- type: APIReference
  url: https://docs.ressl.ai/api-reference/authentication
- type: GettingStarted
  url: https://docs.ressl.ai/quickstart
- type: DeveloperPortal
  url: https://simulation.ressl.ai
- type: SignUp
  url: https://simulation.ressl.ai
- type: GitHubOrganization
  url: https://github.com/ressl-ai
- type: Support
  url: https://join.slack.com/t/resslaiaiagen-czp2639/shared_invite/zt-2vpd5vabp-D9LpsJZRiweb7_OFnvIvhA
- type: LinkedIn
  url: https://www.linkedin.com/company/ressl-ai/

Work with this as data

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

MCP server

One button, every client — Claude, Cursor, VS Code and the rest.

https://apis.io/mcp

Tools for providers

9 MCP tools reach this

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.

All 92 tools →

Call it yourself

curl for this page

This provider

curl "https://apis.io/api/v1/providers/ressl-ai"

All providers

curl "https://apis.io/api/v1/providers?limit=25"

Every operation they expose

curl "https://apis.io/api/v1/providers/ressl-ai/operations?limit=25"

How their score was established

curl "https://apis.io/api/v1/providers/ressl-ai/evidence"

Discovery needs no key. Ratings and market analysis are Pro.

Get an API key

Free tier, no form to fill in. Signing in shares your email address with us — we store it to create your key and to recognise you if you sign in with another provider. See our Privacy Policy and Terms.

GitHub Google LinkedIn

A second provider on the same verified email joins the account you already have.