fastify/fastify

Can another program use it through a documented, machine-readable surface?

• next: [service] L1 A network surface exists: HTTP routes, an MCP server, or a standard protocol listener. (no network surface)
• next: [library] L4 An API reference is generated from the code (autodoc, mkdocstrings, typedoc, …). (no generated API reference)

library ladder · level 3

• ✓ L1 An importable, packaged API exists. package.json npm package
• ✓ L2 The public API is delimited (__all__, an exports map, exported identifiers). package.json package entry point
• ✓ L3 The public API is statically typed (py.typed, type declarations, a typed language). package.json TypeScript types
• ✗ L4 An API reference is generated from the code (autodoc, mkdocstrings, typedoc, …). no generated API reference

service ladder · level 0

• ✗ L1 A network surface exists: HTTP routes, an MCP server, or a standard protocol listener. no network surface
• ✗ L2 A contract exists: a checked-in OpenAPI/GraphQL/protobuf/AsyncAPI spec, a framework-generated spec, MCP tool schemas, or a standard application protocol that off-the-shelf clients speak (RESP, MQTT, gRPC, PostgreSQL wire, …). no machine-readable contract
• ✗ L3 A contract covers its transport: an HTTP contract covers at least 80% of declared routes (generated contracts do), or the application layer over a standard protocol (commands, topics, payloads) is specified in a protocol document or AsyncAPI. no contract
• ✗ L4 A second surface: another transport (HTTP and a protocol, two protocols), an MCP server, a CLI with JSON output, or an SDK. only one programmatic surface

Can integrators rely on it not changing under them?

• next: L2 A changelog exists and marks breaking changes. (no changelog)

all ladder · level 1

• ✓ L1 Releases are versioned (semver tags or versioned changelog sections). 333 semver tags, latest v6.0.0-alpha.4
• ✗ L2 A changelog exists and marks breaking changes. no changelog
• ✗ L3 A deprecation mechanism is used in code (warnings, @deprecated, Deprecation/Sunset headers) or the API is versioned. no deprecation mechanism or API versioning
• ✓ L4 Across tagged releases, no OpenAPI operation, CLI option or __all__ symbol was removed without first being deprecated. 20 tagged releases compared

Can others react to state changes without polling?

• next: L2 Webhooks sent by this system, or a streaming endpoint (SSE, WebSocket). (no outbound webhooks or streams)

service ladder · level 1

• ✓ L1 Internal events exist (signals, queues, an outbox, emitters). fastify.js 1 matchlib/server.js 1 match
• ✗ L2 Webhooks sent by this system, or a streaming endpoint (SSE, WebSocket). no outbound webhooks or streams
• ✗ L3 Signed webhooks registrable through the API, or two mechanisms (webhooks, streams, a broker). one delivery mechanism, or webhooks that are unsigned or not registrable through the API
• ✗ L4 Events are described by AsyncAPI or CloudEvents. no AsyncAPI or CloudEvents contract

Can a machine act with its own revocable, least-privilege identity?

• next: [service] L1 Programmatic authentication (bearer tokens, API keys). (no token auth)
• next: [library] L2 The credential environment variables are documented. (credential environment variables aren't documented)

library ladder · level 1

• ✓ L1 Credentials can be supplied non-interactively (environment variables). scripts/validate-ecosystem-links.js 1 match
• ✗ L2 The credential environment variables are documented. credential environment variables aren't documented
• ✓ L3 No output or log statement includes a credential. no credential in print/log statements
• ✗ L4 Several profiles or scoped credentials per target. no credential profiles

service ladder · level 0

• ✗ L1 Programmatic authentication (bearer tokens, API keys). no token auth
• ✗ L2 Per-client, revocable credentials (managed API keys, service accounts) or OAuth2. no managed keys or OAuth
• ✗ L3 Credentials carry scopes or permissions. no scopes or permissions
• ✗ L4 Standard provisioning or federation (OIDC client credentials, SCIM). no OIDC client credentials or SCIM

Can its data get in and out, in bulk, in open formats, with an explicit schema?

Can an automated caller use it without guessing, and recover from failure?

• next: [service] L2 Field-level validation errors, and paginated lists. (no pagination)
• next: [library] L1 Errors are specific exception types, and library code never calls sys.exit. (no exception classes)

library ladder · level 0

• ✗ L1 Errors are specific exception types, and library code never calls sys.exit. no exception classes
• ✓ L2 Inputs are validated with messages naming the bad argument. lib/four-oh-four.js 1 match
• ✓ L3 Timeouts and retries are configurable. fastify.js 1 matchscripts/validate-ecosystem-links.js 1 match
• ✗ L4 Agent docs, and examples that run as tests (doctests). no agent docs

service ladder · level 1

• ✓ L1 Errors are machine-readable: consistent JSON over HTTP, or a standard protocol's native error replies (RESP errors, MQTT reason codes, gRPC status, SQLSTATE). lib/error-handler.js 7 matcheslib/route.js 7 matches
• ✗ L2 Field-level validation errors, and paginated lists. no pagination
• ✗ L3 Typed errors (RFC 9457 over HTTP, or a standard protocol's typed error codes), idempotent writes (Idempotency-Key), and rate-limit signals. no typed errors
• ✗ L4 Dry-run or validate-only, conditional requests, and agent docs. no dry-run

Can another system run and compose it without a human?

• next: [service] L2 Configured through environment variables, documented: a .env example, a config schema, or docs naming at least half of the variables the code reads. (the environment variables aren't documented)
• next: [library] L3 Published to a public registry, with at most 10 runtime dependencies. (not published to a registry)

library ladder · level 2

• ✓ L1 Importable from source. package.json npm package
• ✓ L2 Installable as a package (a package manifest). package.json package manifest
• ✗ L3 Published to a public registry, with at most 10 runtime dependencies. not published to a registry
• ✗ L4 Optional features behind extras/features. no optional extras

service ladder · level 1

• ✓ L1 Runnable from source with documented steps (a README with commands). README.md
• ✗ L2 Configured through environment variables, documented: a .env example, a config schema, or docs naming at least half of the variables the code reads. the environment variables aren't documented
• ✗ L3 A container image. no Dockerfile
• ✗ L4 Composition artifacts (compose, Helm, IaC). no compose/Helm/IaC

Can behaviour be added without modifying the code?

• next: L2 The docs show how to add behaviour through those seams (even in-tree). (no registration functions to document)

all ladder · level 1

• ✓ L1 Internal seams: a registry, registration function or plugin manager. types/instance.d.ts 17 matchesfastify.js 3 matches
• ✗ L2 The docs show how to add behaviour through those seams (even in-tree). no registration functions to document
• ✗ L3 Out-of-tree extensions are discovered (entry points, a plugin directory, configuration) without editing the package. extensions must be added inside the package
• ✗ L4 The extension API is versioned, has lifecycle hooks, and has example extensions. the extension API isn't versioned

Can an operator, or an orchestrating agent, tell whether it works and why not?

• next: [service] L1 A health or readiness endpoint, or a container healthcheck. (no health endpoint or healthcheck)
• next: [library] L3 Optional metrics or tracing hooks. (no metrics or tracing hooks)

library ladder · level 2

• ✓ L1 Logs through a standard logger namespace and never prints from library code. fastify.js 11 matcheslib/context.js 5 matches
• ✓ L2 Log levels are used meaningfully (at least two levels). levels: debug, error, info, trace, warn
• ✗ L3 Optional metrics or tracing hooks. no metrics or tracing hooks
• ✗ L4 OpenTelemetry instrumentation available. no OpenTelemetry instrumentation

service ladder · level 0

• ✗ L1 A health or readiness endpoint, or a container healthcheck. no health endpoint or healthcheck
• ✓ L2 Structured logs. lib/logger-pino.js 6 matcheslib/logger-factory.js 1 match
• ✗ L3 Metrics. no metrics
• ✗ L4 Distributed tracing (OpenTelemetry). no tracing

Can an agent change it safely with limited context?

• next: L3 At least 90% of modules fit 32k tokens and no file exceeds 12k; test/source token ratio at least 0.3; at least 70% of the code is typed. (67% of modules fit 32k tokens; 1 files over 12k; 35% of code is typed (< 70%))

all ladder · level 2

• ✓ L1 A README and some tests. README.mdtest/404s.test.js 226 test files
• ✓ L2 CI runs the tests; applications pin dependencies (libraries and zero-dependency projects are exempt). .github/workflows/backport.yml.github/workflows/ci-alternative-runtime.yml
• ✗ L3 At least 90% of modules fit 32k tokens and no file exceeds 12k; test/source token ratio at least 0.3; at least 70% of the code is typed. 67% of modules fit 32k tokens; 1 files over 12k; 35% of code is typed (< 70%)
• ✗ L4 No import cycles, and agent docs (AGENTS.md, CLAUDE.md, llms.txt). 1 import cycles (largest: fastify.js, lib/four-oh-four.js, lib/log-controller.js)