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Fly.io vs Railway

Railway scores higher on the AgentReady, 87/100 against 53/100. They differ on 10 of the 41 signals. Which ones decides whether an agent can adopt them without a person watching.

What each one is

Fly.io. Fly.io provides real hardware-isolated Linux computers (called Sprites and Machines) for agents, evals, and tools, with a pay-as-you-go model where billing goes to zero when not in use.

Railway. Railway is an all-in-one intelligent cloud provider that makes it easy to provision infrastructure, develop locally, and deploy to the cloud.

Where Fly.io is ahead

Fly.io passes search discoverable and public docs discoverable, and Railway does not. That is discover, whether an agent can find the product at all without being told it exists.

It also holds adopt: official typescript sdk and official python sdk. Railway misses those.

And on operate, canonical workflow succeeds and observable execution. Railway misses those.

Where Railway is ahead

Railway passes clear product positioning and llms-full.txt / full agent docs, and Fly.io does not. That is discover, whether an agent can find the product at all without being told it exists.

It also holds understand: authentication documented. Fly.io misses it.

And on adopt, free trial or free allowance. Fly.io misses it.

What neither does

Both fail structured api reference, openapi / spec quality, request examples provided, response examples provided, errors and status codes documented, limits / constraints documented, no mandatory sales call, programmatic credential creation, fast time to first request, copyable quickstart, structured, predictable output, machine-readable errors, retry behavior documented, idempotency support, rate-limit behavior predictable. If your agent needs any of those, you will be building it yourself either way.

Score, pillar by pillar

The AgentReady splits into four pillars, scored separately, because a product can be easy to find and still impossible to adopt.

Discover. Railway leads 83 to 80. Fly.io misses clear product positioning, llms-full.txt / full agent docs; Railway misses search discoverable, public docs discoverable.

Understand is whether an agent can read the docs and work out how the API behaves before calling it. Railway leads 100 to 23. Fly.io misses structured api reference, openapi / spec quality, authentication documented, request examples provided, response examples provided, errors and status codes documented, limits / constraints documented; Railway misses structured api reference, openapi / spec quality, request examples provided, response examples provided, errors and status codes documented, limits / constraints documented.

Adopt. Railway leads 88 to 55. Fly.io misses no mandatory sales call, agent-compatible signup flow, programmatic credential creation, free trial or free allowance, fast time to first request, copyable quickstart; Railway misses no mandatory sales call, programmatic credential creation, fast time to first request, copyable quickstart, official typescript sdk, official python sdk.

Operate. Railway leads 78 to 53. Fly.io misses structured, predictable output, machine-readable errors, retry behavior documented, idempotency support, rate-limit behavior predictable; Railway misses canonical workflow succeeds, structured, predictable output, machine-readable errors, retry behavior documented, idempotency support, rate-limit behavior predictable, observable execution.

Pricing

Fly.io starts at $29/mo. Railway does not publish one and has a free tier.

Signal by signal

Which to pick

Fly.io clears more of the signals an agent needs, so it is the safer default for unattended use. Full profiles: Fly.io and Railway. Alternatives to each: Fly.io, Railway.

An agent can fetch this as data: POST /v1/compare {"slugs": ["fly", "railway"]}