Kotoba

Kotoba Technologies is a Japan-founded frontier voice AI company building a foundational real-time speech model and simultaneous translation technology. Its developer platform exposes three JSON-over-WebSocket realtime capabilities — ASR (automatic speech recognition with live transcript deltas), STS (speech-to-speech translation that emits both a source transcript and synthesized target-language audio over one connection), and TTS (streaming text-to-speech) — alongside a REST transcription API for batch and offline workflows built on a submit-and-poll job model. Supported languages span English, Japanese, Korean, Chinese and Spanish. Each realtime channel is described by a published AsyncAPI 2.6.0 document and each REST surface by OpenAPI 3.1, with a first-party Python SDK, an llms.txt agent index, and a live remote MCP documentation server. The APIs are in private alpha, available to selected customers on request.

Kotoba publishes 1 API on the APIs.io network: transcriptionApi API. Tagged areas include Company, Artificial Intelligence, Machine-Learning, Voice, and Speech Recognition.

The Kotoba catalog on APIs.io includes 3 event-driven AsyncAPI specifications.

Kotoba’s developer surface includes documentation, API reference, getting-started guide, support, signup flow, engineering blog, authentication, and 28 more developer resources.

🌐 Visit website 📡 Source on GitHub

42.8/100 developing ▬ flat Agent 29/100 agent aware open core · MIT Full breakdown ↓
scored 2026-09-08 · rubric v0.20.0

4 APIs 1 MCP Servers

Company Artificial Intelligence Machine-Learning Voice Speech Recognition Speech-to-Text Text-to-Speech Translation Real-Time WebSockets Audio Transcription

Kin Score

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

Composite quality — 42.8/100 · developing

Contract Quality 11.5 / 20

Developer Ergonomics 10.6 / 16

Access Clarity 5.5 / 16

Operational Transparency 1.9 / 10

Contract Governance 0.4 / 10

Discoverability 6.5 / 8

Open Source Surface 2.5 / 10

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 29/100 · agent aware

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 8 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 6 / 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

Open Source Surface applies to this provider. This product is open source and we read its repository directly, so Open Source Surface carries 10 points of the composite. It is scored from what the repository actually publishes — a security policy, a contribution guide, a release history, a code of conduct — read live from the provider rather than inferred from our own catalog pointers. This facet adds; nothing was taken away to make room for it. An open-source project is not excused from the commercial facets, because exemption would strip it of the points it does earn. If we have the wrong repository, or this product is not open source, say so on your provider repo and we will drop the facet rather than have you publish against 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 80 points between them, because the conditional facet above carries the other 20. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 80% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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/kotoba: 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 1

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

Kotoba transcriptionApi API

The transcriptionApi API from Kotoba — 2 operation(s) for transcriptionapi.

Open Collections 2

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

API Collection

OPEN COLLECTION

Live (WebSocket) transcriptionApi API

OPEN COLLECTION

MCP Servers 1

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

Kotoba MCP Server

MCP SERVER

Event Specifications 3

AsyncAPI definitions for this provider's event-driven and streaming APIs.

Live (WebSocket)

ASYNCAPI

Live (WebSocket)

ASYNCAPI

Live (WebSocket)

ASYNCAPI

Security Posture 2

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

Kotoba Authentication

http/client-secret · 3 schemes

SECURITY

Kotoba Domain Security

TLSv1.3 · HSTS

SECURITY

Agentic Access 1

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

Kotoba Agentic Access

2 operations · 1 acting

AGENTIC

Resources

Get Started 4

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

GettingStarted

GettingStarted

SignUp

SignUp

Login

Documentation 4

Reference material describing how the API behaves

Documentation

APIReference

OpenAPI

AsyncAPI

Agent Surfaces 5

MCP servers, agent skills, and machine-readable catalogs

MCPServer

LLMsTxt

AgentSkill

AgenticAccess

WellKnown

Design & Contract 5

Pagination, idempotency, versioning, errors, and events

Conventions

ErrorCatalog

DataModel

Conformance

Lifecycle

Build 4

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

SourceCode

Packages

SDKs

Access & Security 2

Authentication, authorization, and security posture

Authentication

Authentication

DomainSecurity

DomainSecurity

Operate 3

Status, limits, changes, and where to get help

IssueTracker

IssueTracker

Releases

Releases

Support

Support

Commercial 3

Pricing, plans, and the legal terms of use

License

License

TermsOfService

TermsOfService

PrivacyPolicy

PrivacyPolicy

Company 3

The organization behind the API

Website

Website

Blog

Blog

LinkedIn

Other 2

Properties that don't map to a standard resource type

Overlay

Overlay

Source (apis.yml)

aid: kotoba
name: Kotoba
description: Kotoba Technologies is a Japan-founded frontier voice AI company building a foundational real-time speech model
  and simultaneous translation technology. Its developer platform exposes three JSON-over-WebSocket realtime capabilities
  — ASR (automatic speech recognition with live transcript deltas), STS (speech-to-speech translation that emits both a source
  transcript and synthesized target-language audio over one connection), and TTS (streaming text-to-speech) — alongside a
  REST transcription API for batch and offline workflows built on a submit-and-poll job model. Supported languages span English,
  Japanese, Korean, Chinese and Spanish. Each realtime channel is described by a published AsyncAPI 2.6.0 document and each
  REST surface by OpenAPI 3.1, with a first-party Python SDK, an llms.txt agent index, and a live remote MCP documentation
  server. The APIs are in private alpha, available to selected customers on request.
url: https://raw.githubusercontent.com/api-evangelist/kotoba/refs/heads/main/apis.yml
deliveryModel:
  model: open-core
  license: MIT
  open_source: true
  commercial: true
  callable_host: true
  label: Open core · an OSS project plus a commercial hosted product
  confidence: high
  source:
  - license
  - 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://framerusercontent.com/images/7OW09ZoQn6c3oPwAHQgP3DCXI.png
x-type: company
x-source: vc-portfolio
x-backed-by:
- kindred-ventures
x-tier: enriched
x-tier-reason: openapi-asyncapi-mcp-sdk-published
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-07-19'
tags:
- Company
- Artificial Intelligence
- Machine-Learning
- Voice
- Speech Recognition
- Speech-to-Text
- Text-to-Speech
- Translation
- Real-Time
- WebSockets
- Audio
- Transcription
tags_raw:
- Company
- Artificial Intelligence
- Machine Learning
- Voice
- Speech Recognition
- Speech to Text
- Text to Speech
- Translation
- Real Time
- WebSockets
- Audio
- Transcription
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
apis:
- aid: kotoba:kotoba-transcriptionapi-api
  name: Kotoba transcriptionApi API
  description: The transcriptionApi API from Kotoba — 2 operation(s) for transcriptionapi.
  humanURL: https://docs.kotoba.tech/s2t/batch
  baseURL: https://api.kotobatech.ai
  tags: []
  tags_raw:
  - transcriptionApi
  properties:
  - type: OpenAPI
    url: openapi/kotoba-transcriptionapi-api-openapi.yml
  - type: Documentation
    url: https://docs.kotoba.tech/s2t/batch
  - type: AsyncAPI
    url: asyncapi/kotoba-asr-asyncapi.yml
  - type: Documentation
    url: https://docs.kotoba.tech/overview/capabilities/speech-to-text
  - type: AsyncAPI
    url: asyncapi/kotoba-sts-asyncapi.yml
  - type: Documentation
    url: https://docs.kotoba.tech/overview/capabilities/speech-to-speech
  - type: AsyncAPI
    url: asyncapi/kotoba-tts-asyncapi.yml
  - type: Documentation
    url: https://docs.kotoba.tech/overview/capabilities/text-to-speech
common:
- type: IssueTracker
  url: https://github.com/kotoba-tech/kotoba-python/issues
- type: Releases
  url: https://github.com/kotoba-tech/kotoba-python/releases
- type: License
  name: MIT
  url: https://github.com/kotoba-tech/kotoba-python/blob/main/LICENSE
- type: Website
  url: https://kotoba.tech/
- type: DeveloperPortal
  url: https://docs.kotoba.tech/
- type: Documentation
  url: https://docs.kotoba.tech/
- type: APIReference
  url: https://docs.kotoba.tech/s2t/streaming/asr/asr
- type: GettingStarted
  url: https://docs.kotoba.tech/overview/introduction
- type: Support
  url: https://site.kotoba.tech/contact
- type: SignUp
  url: https://app.kotoba.tech/
- type: Login
  url: https://app.kotoba.tech/
- type: Blog
  url: https://site.kotoba.tech/news
- type: TermsOfService
  url: https://dashboard.kotobatech.ai/terms_en.html
- type: PrivacyPolicy
  url: https://dashboard.kotobatech.ai/privacy_en.html
- type: GitHubOrganization
  url: https://github.com/kotoba-tech
- type: SourceCode
  url: https://github.com/kotoba-tech/kotoba-python
- type: X
  url: https://x.com/kotoba_tech
- type: LinkedIn
  url: https://www.linkedin.com/company/kotoba-tech/
- type: Authentication
  url: authentication/kotoba-authentication.yml
- type: OpenAPI
  url: openapi/_original/kotoba-transcription-openapi-original.yml
- type: AsyncAPI
  url: asyncapi/kotoba-asr-asyncapi.yml
- type: Packages
  url: packages/kotoba-packages.yml
- type: SDKs
  url: packages/kotoba-packages.yml
- type: MCPServer
  url: mcp/kotoba-mcp.yml
- type: LLMsTxt
  url: llms/kotoba-llms.txt
- type: AgentSkill
  url: skills/_index.yml
- type: AgenticAccess
  url: agentic-access/kotoba-agentic-access.yml
- type: Conventions
  url: conventions/kotoba-conventions.yml
- type: ErrorCatalog
  url: errors/kotoba-problem-types.yml
- type: DataModel
  url: data-model/kotoba-data-model.yml
- type: Conformance
  url: conformance/kotoba-conformance.yml
- type: Lifecycle
  url: lifecycle/kotoba-lifecycle.yml
- type: WellKnown
  url: well-known/kotoba-well-known.yml
- type: DomainSecurity
  url: security/kotoba-domain-security.yml
- type: Overlay
  url: overlays/kotoba-transcription-overlay.yaml
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence

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