Gutendex
Gutendex is a simple, self-hosted JSON-based web API for serving book catalog information from Project Gutenberg, providing structured metadata for over 70,000 free ebooks including titles, authors, subjects, bookshelves, languages, copyright status, media types, downloadable formats, and download counts. The hosted instance at gutendex.com runs the open-source Django project by Gareth B. Johnson under the MIT license.
Real signal across most facets with visible, nameable gaps — the contract exists but is thin, or the portal is good while governance and commercial terms are absent.
API Evangelist profiles Gutendex the way a machine reads it — 45 machine-readable artifacts across 1 API, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — Gutendex scores 45.5/100 (developing), with a separate agent-readiness read of 29/100 (agent aware). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance. Every facet and dimension name is a link: it opens that measurement's page on APIs.io, where the rating runs across the whole catalog — the exact checks that feed it, how every profiled provider distributes on it, and who is at the top of it.
Kin Score
How this is scored →scored 2026-09-08 · rubric v0.20.0
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How we profile Gutendex
Each block below is one kind of artifact we hold for Gutendex. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 1
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
Gutendex Books API
Query and retrieve metadata for Project Gutenberg ebooks.
Open Collections 3
Open, tool-agnostic collections carry the same runnable value as Postman without locking you to one client — the portable, forkable form of the same exercise.
Open, tool-agnostic API collections (OpenAPI-derived and Bruno).
Pricing Plans 1
Pricing is part of the interface. Machine-readable plans tell you what a tier costs and includes before you commit — one of the things the Kin Score reads for access clarity — renamed from commercial clarity in rubric 0.12, because a free statutory interface has access terms and no commercial ones.
Published pricing tiers and plan structures.
Rate Limits 1
Rate limits are the difference between a demo that works and a production integration that doesn't fall over. Publishing them is an operational-transparency signal — and a hard requirement for any agent that plans its own throughput.
Documented rate limits and quota policies.
Gutendex Rate Limits
RATE LIMITSFeatures 8
The notable capabilities this provider advertises, captured as structured features so they can be searched and compared instead of read one landing page at a time.
Notable capabilities this provider offers.
Free Public API
No API key, no signup, no rate limit documented; gutendex.com is openly available.
70,000+ Ebook Catalog
Mirrors the full Project Gutenberg catalog of free public-domain ebooks.
Rich Filtering
Filter by author birth/death year, copyright status, language, MIME type, IDs, search keywords, and topic.
Multiple Sort Orders
Sort results by popularity (default), ascending ID, or descending ID.
Multi-format Downloads
Each book exposes a Format object mapping MIME types (HTML, EPUB, MOBI, plain text, JPEG) to direct download URLs.
Bookshelves and Subjects
Books are tagged with Library of Congress subject headings and curated Project Gutenberg bookshelves.
Multi-language Support
Books are indexed by two-character ISO language codes; filter by multiple languages at once.
Self-Hostable
MIT-licensed Django app that operators can run on their own infrastructure with nightly Project Gutenberg catalog sync.
Scroll within the panel for all 8 ·
Semantic Vocabularies 1
JSON-LD contexts give the data shared meaning across APIs. We profile them because semantics are what let a machine reconcile 'customer' here with 'customer' somewhere else.
JSON-LD contexts and semantic vocabularies used across these APIs.
Gutendex Context
JSON-LDSpectral Rules 2
Governance rulesets we run against this provider's specs — the automated checks behind parts of the score. Profiling them makes the quality bar explicit and re-runnable, not a matter of opinion.
Gutendex API Rules
SPECTRALGutendex API Rules
SPECTRALJSON Schema 5
Standalone JSON Schema definitions describe the data models behind the API. We profile them so the shapes are validatable on their own — useful long after a single request is forgotten.
Standalone JSON Schema definitions for this provider's data models.
JSON Structure 5
JSON Structure captures the data shapes in a form built for tooling — a complement to JSON Schema that keeps the model machine-legible.
JSON Structure definitions describing this provider's data shapes.
Gutendex Book List Structure
JSON STRUCTUREGutendex Book Structure
JSON STRUCTUREGutendex Error Structure
JSON STRUCTUREGutendex Format Structure
JSON STRUCTUREGutendex Person Structure
JSON STRUCTUREExamples 6
Real request and response payloads are what turn a spec from abstract into obvious — and they're one of the twelve things an agent needs to call an API correctly on the first try.
Example request and response payloads for these APIs.
Gutendex Book Example
EXAMPLEGutendex Error Example
EXAMPLEGutendex Format Example
EXAMPLEGutendex Get Book Example
EXAMPLEGutendex List Books Example
EXAMPLEGutendex Person Example
EXAMPLESecurity Posture 1
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Agentic Access 1
An x-agentic-access contract marks which operations are safe for an agent to run on its own and which need a human in the loop. It is the difference between an API an agent can use and one it can use safely.
Recommended x-agentic-access execution contracts for AI agents.
Use Cases 6
What developers actually build with this provider — captured so the catalogue answers 'what is this for', not just 'what does this expose'.
What developers build with this provider.
Literature Analytics
Power large-scale analysis of public-domain literature by ingesting the structured Project Gutenberg catalog.
Educational Apps
Build classroom or self-study apps that surface public-domain texts by subject, author, or reading level.
Reading Recommendation Engines
Use the download_count and bookshelf data to recommend popular classics or themed reading lists.
Digital Library Backends
Power library catalog interfaces and ebook reader apps with a clean JSON facade over Project Gutenberg's XML archives.
Natural Language Processing Datasets
Use the catalog to discover bulk text downloads for training language models on public-domain corpora.
Citation and Reference Tools
Power author/title lookup widgets in citation managers and academic writing tools.
Integrations 4
Pre-built integrations with other platforms tell you where this provider already fits in a stack.
Pre-built integrations with other platforms and tools.
Project Gutenberg
Upstream source. Gutendex nightly-ingests the official Project Gutenberg XML catalog and republishes it as JSON.
Django REST Framework
Built on Django + Django REST Framework. Operators can extend the API with additional viewsets.
Model Context Protocol
Community-maintained MCP servers expose Project Gutenberg / Gutendex to LLM agents (bobbyhouse, vellankis-space, nasimcoderex).
PostgreSQL / SQLite
Default Django storage backends used by self-hosted instances for catalog persistence.
Resources
Every other property we hold for Gutendex — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Get Started 1
Portal, sign-up, and the first successful call
Documentation 3
Reference material describing how the API behaves
Agent Surfaces 1
MCP servers, agent skills, and machine-readable catalogs
Design & Contract 3
Pagination, idempotency, versioning, errors, and events
Build 4
SDKs, sample code, and the tooling you integrate with
Access & Security 2
Authentication, authorization, and security posture
Operate 2
Status, limits, changes, and where to get help
Commercial 3
Pricing, plans, and the legal terms of use
Company 1
The organization behind the API
Other 1
Properties that don't map to a standard resource type
← All providers · Data indexed from github.com/api-evangelist/gutendex · machine-readable index on apis.io
This is an independent, third-party profile of Gutendex, published by API Evangelist. We do not operate, host, resell, or support these APIs, and we are not affiliated with or endorsed by the company unless stated above. Everything here is built from publicly available information — the company's own site, developer portal, documentation, public repositories, and the specifications it publishes for public use. Nothing is obtained by breaching a system, defeating an access control, or using credentials.
The Kin Score and Agent Readiness rating are independently calculated assessments of a company's public API artifacts, scored against a published rubric. They are not certifications, endorsements, security assessments, or audits.
Corrections, re-scores, and removal are free — no partnership or purchase required, and you do not need to justify the request. A removed company is recorded as unrated, never scored zero for having asked. Acknowledgement within one business day; removal within two.
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