Project Gutenberg

Project Gutenberg is a free ebook library providing access to over 75,000 public domain books via the Gutendex REST API. The API enables developers to search and retrieve bibliographic metadata for books and authors, filter by language, copyright status, topic, and MIME type, and access download links for multiple formats including EPUB, Kindle, HTML, and plain text. Project Gutenberg has pioneered free ebooks since 1971 and the Gutendex API makes its catalog programmatically accessible via a simple JSON REST interface with no authentication required.

Project Gutenberg is listed with 1 API on the APIs.io network: Gutendex API. Tagged areas include Books, Ebooks, Public Domain, Literature, and Library.

Project Gutenberg’s developer surface includes documentation, engineering blog, pricing, and 8 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

20.0/100 emerging ▬ flat Agent 14/100 agent aware Front door AI 1/6 silent Heartbeat 95/100 alive saas Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

AccessFreeOpen⚡ Free to try

1 API

Books Ebooks Public Domain Literature Library Metadata EPUB

Kin Score

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

Composite quality — 20.0/100 · emerging

Contract Quality 5.1 / 21

Developer Ergonomics 2.0 / 17

Access Clarity 2.7 / 17

Operational Transparency 3.2 / 11

Contract Governance 0.0 / 10

Discoverability 5.6 / 9

Regulatory Posture 0.9 / 15

Agent readiness — 14/100 · agent aware

Machine-Readable Contract 18 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 0 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 7 / 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 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Education & Research 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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<a href="https://apis.io/providers/gutenberg/"><img src="https://apis.io/badge/gutenberg/card.svg" alt="Project Gutenberg on APIs.io — Kin Score by API Evangelist"></a>

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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
Machine-Readable Auth +10 pts — a served openid-configuration/oauth-authorization-server carrying `issuer` (served), else the securitySchemes class in the provider OpenAPIs — bound (mutualTLS, DPoP, Signature) > negotiable (oauth2 authorizationCode/clientCredentials, openIdConnect) > bearer (http bearer, apiKey)
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

11 more unmet checks in the Agent Readiness table above.

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

Contract Quality scores 24.0 — up to +19.0 composite points
Developer Ergonomics scores 11.9 — up to +17.6 composite points
Access Clarity scores 15.8 — up to +16.8 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/gutenberg/apis.yml: open an issue on github.com/api-evangelist/gutenberg 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 →

Standards implemented 1

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.

OpenAPI

measured — observed by APIs.io (published)

APIs 1

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

Gutendex API

Gutendex is a JSON web API for Project Gutenberg ebook metadata. It provides access to the catalog of 75,000+ public domain books with filtering by language, copyright status, t...

Project Gutenberg API pricing

Not yet checked against Project Gutenberg's own pricing page. Compiled by API Evangelist; confirm before you rely on a figure. A free plan or tier is listed.

Plan	Price
Free	Free
Self-Hosted	Free

Plan details, limits and sources →

Rate limits

Project Gutenberg Website - Robot Access Delay: 1

Compiled by API Evangelist, not yet checked against Project Gutenberg's documentation. All 3 limits →

Pricing Plans 1

Published pricing tiers and plan structures.

Gutenberg Plans Pricing

2 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Gutenberg Rate Limits

3 limits

RATE LIMITS

FinOps 1

Cost, billing, and metering signals for API financial operations.

Gutenberg Finops

FINOPS

Security Posture 1

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

Gutenberg Domain Security

TLSv1.3

SECURITY

Resources

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Build 1

SDKs, sample code, and the tooling you integrate with

GitHubOrg

GitHubOrg

Access & Security 1

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Operate 2

Status, limits, changes, and where to get help

StatusPage

StatusPage

RateLimits

RateLimits

Commercial 3

Pricing, plans, and the legal terms of use

Pricing

Pricing

Plans

Plans

FinOps

FinOps

Company 2

The organization behind the API

Website

Website

Blog

Blog

Other 1

Properties that don't map to a standard resource type

Source (apis.yml)

aid: gutenberg
name: Project Gutenberg
description: Project Gutenberg is a free ebook library providing access to over 75,000 public domain books via the Gutendex
  REST API. The API enables developers to search and retrieve bibliographic metadata for books and authors, filter by language,
  copyright status, topic, and MIME type, and access download links for multiple formats including EPUB, Kindle, HTML, and
  plain text. Project Gutenberg has pioneered free ebooks since 1971 and the Gutendex API makes its catalog programmatically
  accessible via a simple JSON REST interface with no authentication required.
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: false
  label: Hosted service · you call their endpoint
  confidence: medium
  source:
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: free
  onboarding: open
  trial: false
  try_now: true
  public: true
  gated: none
  gated_source:
  - onboarding
  label: Free · Open access
  confidence: low
  source:
  - plans
  - security
  generated: '2026-11-06'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/gutenberg.png
url: https://raw.githubusercontent.com/api-evangelist/gutenberg/refs/heads/main/apis.yml
created: '2026-06-13'
modified: '2026-06-13'
specificationVersion: '0.23'
tags:
- Books
- Ebooks
- Public Domain
- Literature
- Library
- Metadata
- EPUB
apis:
- aid: gutenberg:gutendex
  name: Gutendex API
  description: Gutendex is a JSON web API for Project Gutenberg ebook metadata. It provides access to the catalog of 75,000+
    public domain books with filtering by language, copyright status, topic, author lifespan, and MIME type. The API returns
    paginated JSON results including book titles, authors, subjects, bookshelves, download formats, and download counts. No
    authentication or API key is required.
  image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/apis-json-logo.jpg
  humanURL: https://gutendex.com/
  baseURL: https://gutendex.com
  tags:
  - Books
  - Ebooks
  - Public Domain
  - Metadata
  - Literature
  properties:
  - type: Documentation
    url: https://gutendex.com/
  - type: OpenAPI
    url: https://gutendex.com/books
common:
- type: DomainSecurity
  url: security/gutenberg-domain-security.yml
- type: Website
  url: https://www.gutenberg.org/
- type: Documentation
  url: https://gutendex.com/
- type: GitHubOrg
  url: https://github.com/gutenbergtools
- type: Blog
  url: https://www.gutenberg.org/help/
- type: Pricing
  url: https://gutendex.com/
- type: StatusPage
  url: https://www.gutenberg.org/
- type: X
  url: https://twitter.com/gutenberg_org
- type: Plans
  url: plans/gutenberg-plans-pricing.yml
- type: RateLimits
  url: rate-limits/gutenberg-rate-limits.yml
- type: FinOps
  url: finops/gutenberg-finops.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com

Project Gutenberg API — frequently asked questions

Does Project Gutenberg have an API?

Yes. APIs.io lists 1 API from Project Gutenberg, including Gutendex API.

Is there an OpenAPI specification for the Project Gutenberg API?

Yes. APIs.io indexes 1 OpenAPI specification for Project Gutenberg, each linked for download from this page.

How much does the Project Gutenberg API cost?

APIs.io lists 2 pricing plans for Project Gutenberg, with each plan's price, limits and inclusions under Pricing on this page.

Is the Project Gutenberg API ready for AI agents?

Project Gutenberg has a Kin Score of 20.0 out of 100 (emerging) and an Agent Readiness score of 13.6 (agent-aware), scored by API Evangelist on 2026-11-06.

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