Stalwart

Stalwart Labs develops an open-source mail and collaboration server offering JMAP, IMAP4, POP3, SMTP, CalDAV, CardDAV, and WebDAV support. Built in Rust, it emphasizes security, scalability, and ease of operation for enterprises and developers seeking a modern, self-hosted communication platform.

Stalwart is listed with 3 APIs on the APIs.io network: Auth overview API, core API, and HTTP overview API. Tagged areas include Email, OpenSource, Rust, Collaboration, and Server.

The Stalwart catalog on APIs.io includes 1 JSON-LD context and 1 Spectral governance ruleset.

Stalwart’s developer surface includes documentation, API reference, support, engineering blog, pricing, and 16 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

32.6/100 thin Agent 15/100 agent aware Full breakdown ↓
scored 2026-10-31 · rubric v0.25.0 · Show this score on your site →

3 APIs

EmailOpenSourceRust CollaborationServerCompany

Kin Score

Kin Score How this is scored →
scored 2026-10-31 · rubric v0.25.0

Composite quality — 32.6/100 · thin

Contract Quality 5.4 / 21

Developer Ergonomics 5.7 / 17

Access Clarity 7.2 / 17

Operational Transparency 1.2 / 11

Contract Governance 2.0 / 10

Discoverability 6.1 / 9

Regulatory Posture 2.5 / 15

Agent readiness — 15/100 · agent aware

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 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 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

Pagination 5 / 5

Distinct Operations 0 / 3

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) 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 could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% 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):

MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship
Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author
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)
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes
Rate-Limit Signaling +7 pts — OpenAPI responses document X-RateLimit-* / RateLimit headers (verified), else a rate_limits artifact or RateLimits link (documented)

12 more unmet checks in the Agent Readiness table above.

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

Contract Quality scores 25.6 — up to +18.6 composite points
Developer Ergonomics scores 33.3 — up to +13.3 composite points
Operational Transparency scores 10.5 — up to +11.6 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/stalwart/apis.yml: open an issue on github.com/api-evangelist/stalwart 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 →

APIs 3

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

Stalwart Auth overview API

Stalwart Auth overview API as documented publicly: 21 operations. Contract generated from the documentation by API Evangelist (2026-10-28); not the provider's own document.

Stalwart core API

Stalwart core API as documented publicly: 4 operations. Contract generated from the documentation by API Evangelist (2026-10-28); not the provider's own document.

Stalwart HTTP overview API

Stalwart HTTP overview API as documented publicly: 19 operations. Contract generated from the documentation by API Evangelist (2026-10-28); not the provider's own document.

Pricing Plans 1

Published pricing tiers and plan structures.

Stalwart Plans Pricing

8 plans

PLANS

Semantic Vocabularies 1

JSON-LD contexts and semantic vocabularies used across these APIs.

Stalwart Context

23 classes · 55 properties

JSON-LD

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

Stalwart API Rules

9 rules · 8 errors 1 info

SPECTRAL

JSON Schema 14

Standalone JSON Schema definitions for this provider's data models.

GetApiAccountResponse

3 properties

JSON SCHEMA

GetApiAuthClientResponse

11 properties

JSON SCHEMA

GetScimV2UsersResponse

2 properties

JSON SCHEMA

PostApiAuthRequest

7 properties

JSON SCHEMA

PostApiAuthResponse

4 properties

JSON SCHEMA

PostApiCalendarRsvpRequest

3 properties

JSON SCHEMA

PostApiCalendarRsvpResponse

4 properties

JSON SCHEMA

PostAuthDeviceRequest

2 properties

JSON SCHEMA

PostAuthDeviceResponse

6 properties

JSON SCHEMA

PostAuthIntrospectResponse

6 properties

JSON SCHEMA

PostAuthRegisterRequest

3 properties

JSON SCHEMA

PostAutodiscoverAutodiscoverXmlRequest

1 properties

JSON SCHEMA

PostAutodiscoverAutodiscoverXmlResponse

3 properties

JSON SCHEMA

PostUsersRequest

2 properties

JSON SCHEMA

Scroll for all 14

Security Posture 2

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

Stalwart Domain Security

TLSv1.3 · DNSSEC · DMARC

SECURITY

Stalwart Vulnerability Disclosure

security.txt · contact published

SECURITY

Resources

Get Started 1

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

Documentation 2

Reference material describing how the API behaves

Documentation

Documentation

APIReference

APIReference

Agent Surfaces 2

MCP servers, agent skills, and machine-readable catalogs

LLMsTxt

LLMsTxt

WellKnown

WellKnown

Design & Contract 5

Pagination, idempotency, versioning, errors, and events

Spectral

JSONLD

Vocabulary

DataModel

Conformance

Access & Security 4

Authentication, authorization, and security posture

Security

Security

SecurityTxt

SecurityTxt

VulnerabilityDisclosure

VulnerabilityDisclosure

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

Support

Support

Commercial 2

Pricing, plans, and the legal terms of use

Plans

Plans

Pricing

Pricing

Company 2

The organization behind the API

Website

Website

Blog

Blog

Other 2

Properties that don't map to a standard resource type

Hosts

Hosts

Vendors

Vendors

Source (apis.yml)

aid: stalwart
name: Stalwart
image: https://stalw.art/img/stalwart-social-card.jpg
description: Stalwart Labs develops an open-source mail and collaboration server offering JMAP, IMAP4, POP3, SMTP, CalDAV,
  CardDAV, and WebDAV support. Built in Rust, it emphasizes security, scalability, and ease of operation for enterprises and
  developers seeking a modern, self-hosted communication platform.
url: https://raw.githubusercontent.com/api-evangelist/stalwart/refs/heads/main/apis.yml
x-type: company
x-source: harvest:new-submission
x-tier: profiled
x-tier-reason: enrichment pass 2026-10-28 (modular-v1; was harvest)
specificationVersion: '0.20'
created: '2026-10-28'
modified: '2026-10-28'
tags:
- Email
- OpenSource
- Rust
- Collaboration
- Server
- Company
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: Plans
  url: plans/stalwart-plans-pricing.yml
- type: Spectral
  url: rules/stalwart-rules.yml
- type: JSONLD
  url: json-ld/stalwart-context.jsonld
- type: Vocabulary
  url: vocabulary/stalwart-vocabulary.yml
- type: DataModel
  url: data-model/stalwart-data-model.yml
- type: Security
  url: https://stalw.art/legal/security
- type: Conformance
  url: conformance/stalwart-conformance.yml
- type: LLMsTxt
  url: llms/stalwart-llms.txt
- type: SecurityTxt
  url: well-known/stalwart-security.txt
- type: WellKnown
  url: well-known/stalwart-well-known.yml
- type: Hosts
  url: hosts/stalwart-hosts.yml
- type: Vendors
  url: vendors/stalwart-vendors.yml
- type: VulnerabilityDisclosure
  url: security/stalwart-vulnerability-disclosure.yml
- type: DomainSecurity
  url: security/stalwart-domain-security.yml
- type: Website
  url: https://stalw.art/
- type: DeveloperPortal
  url: https://stalw.art/
- type: Documentation
  url: https://stalw.art/docs/
- type: APIReference
  url: https://stalw.art/docs/
- type: Support
  url: https://stalw.art/support/
- type: Blog
  url: https://stalw.art/blog/
- type: Pricing
  url: https://stalw.art/pricing/
apis:
- aid: stalwart:auth-api
  name: Stalwart Auth overview API
  description: 'Stalwart Auth overview API as documented publicly: 21 operations. Contract generated from the documentation
    by API Evangelist (2026-10-28); not the provider''s own document.'
  humanURL: https://stalw.art/docs/auth
  baseURL: https://get.stalw.art
  properties:
  - type: OpenAPI
    url: openapi/_ae-authored/stalwart-auth-openapi-generated.yml
    x-provenance: generated
  - type: JSONSchema
    url: json-schema/stalwart-post-auth-introspect-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-auth-register-request-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-auth-device-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-users-request-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-get-scim-v2-users-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-auth-device-request-schema.json
- aid: stalwart:core-api
  name: Stalwart core API
  description: 'Stalwart core API as documented publicly: 4 operations. Contract generated from the documentation by API Evangelist
    (2026-10-28); not the provider''s own document.'
  humanURL: https://stalw.art/docs/install
  baseURL: https://get.stalw.art
  properties:
  - type: OpenAPI
    url: openapi/_ae-authored/stalwart-core-openapi-generated.yml
    x-provenance: generated
  - type: JSONSchema
    url: json-schema/stalwart-post-autodiscover-autodiscover-xml-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-autodiscover-autodiscover-xml-request-schema.json
- aid: stalwart:http-api
  name: Stalwart HTTP overview API
  description: 'Stalwart HTTP overview API as documented publicly: 19 operations. Contract generated from the documentation
    by API Evangelist (2026-10-28); not the provider''s own document.'
  humanURL: https://stalw.art/docs/http
  baseURL: https://get.stalw.art
  properties:
  - type: OpenAPI
    url: openapi/_ae-authored/stalwart-http-openapi-generated.yml
    x-provenance: generated
  - type: JSONSchema
    url: json-schema/stalwart-get-api-auth-client-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-api-auth-request-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-api-auth-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-api-calendar-rsvp-response-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-post-api-calendar-rsvp-request-schema.json
  - type: JSONSchema
    url: json-schema/stalwart-get-api-account-response-schema.json
x-submission-probe: 200, 2026-10-26
x-coverage:
  state: unreadable
  reason: no-machine-readable-spec
  detail: Documentation pages are HTML only and provide no OpenAPI, AsyncAPI, GraphQL, gRPC, or WSDL specifications.
  evidence:
  - url: https://stalw.art/docs/sieve/reference/
    status: 200
  checked: '2026-10-28'
x-enrichment:
  date: '2026-10-28'
  status: enriched
  artifacts_added: 35
  pass: modular-v1
  engine: identity=local,contract=local,surfaces=local,docs=local,regulatory=local

Stalwart API — frequently asked questions

Does Stalwart have an API?

Yes. APIs.io lists 3 APIs from Stalwart, including Stalwart Auth overview API, Stalwart core API and Stalwart HTTP overview API.

Is there an OpenAPI specification for the Stalwart API?

Yes. APIs.io indexes 3 OpenAPI specifications for Stalwart, each linked for download from this page.

How do I authenticate with the Stalwart API?

Stalwart uses bearer-token authentication.

How much does the Stalwart API cost?

APIs.io lists 8 pricing plans for Stalwart, with each plan's price, limits and inclusions under Pricing Plans on this page.

Is the Stalwart API ready for AI agents?

Stalwart has a Kin Score of 32.6 out of 100 (thin) and an Agent Readiness score of 15.1 (agent-aware), scored by API Evangelist on 2026-10-31.

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