# Fillo developer resources

Last verified: 2026-08-23

Canonical URL: https://fillo.so/developers

Official, first-party resources for building with Fillo. Fillo is headless form infrastructure: render native forms in your own product, or operate forms, responses, webhooks, and publishing from an agent or backend.

## Start without a sales call

- Open the zero-auth editor at https://fillo.so/new. A guest draft stays in the browser until it is claimed.
- Sign up without a card at https://fillo.so/signup. Signup is passwordless and Google and GitHub are also available.
- An agent can create a live preview workspace without a browser: `npx @usefillo/cli@latest agent bootstrap --email you@company.com`. The preview supports up to 3 forms and 10 total responses for 14 days; the emailed claim link saves it to an account.
- Free has no time limit. Everything starts with 30 days free. Current allowances are published at https://fillo.so/pricing.md.

There is no separate mock sandbox: the preview workspace uses the real hosted API with capped, disposable onboarding limits. After claiming it, create scoped `fsk_` project keys in *Settings → Connections → API keys* or with the Fillo CLI.

## Fillo Management API

- Human reference: https://fillo.so/docs/api
- Markdown reference: https://fillo.so/docs/api.md
- OpenAPI 3.1 specification: https://fillo.so/openapi.json
- Public API discovery document: https://fillo.so/api/v1
- Authentication and scopes: https://fillo.so/docs/api#auth and https://fillo.so/docs/api#scopes
- Base path: https://fillo.so/api/v1/manage

Management routes use server-side bearer keys beginning with `fsk_`. Keep them out of browser bundles. The API returns `RateLimit-Policy` on responses and returns `RateLimit`, compatibility rate-limit fields, and `Retry-After` on a 429.

## Fillo webhooks

- Setup, event shapes, signature verification, and retry behavior: https://fillo.so/docs/webhooks
- Markdown reference: https://fillo.so/docs/webhooks.md

Fillo webhooks are signed, delivered at least once, and use `X-Fillo-Delivery-Id` as the idempotency key.

## Fillo MCP server

- Canonical Streamable HTTP endpoint: https://fillo.so/api/mcp
- Predictable discovery endpoint: https://fillo.so/.well-known/mcp
- Public server card: https://fillo.so/.well-known/mcp/server-card.json
- OAuth protected-resource metadata: https://fillo.so/.well-known/oauth-protected-resource
- Setup and tool reference: https://fillo.so/docs/mcp

The remote server is stateless and uses OAuth 2.1 with PKCE and Dynamic Client Registration. For clients that only support local stdio servers, run `npx -y @usefillo/mcp`.

## Official Fillo CLI and SDKs

- CLI on npm: https://www.npmjs.com/package/@usefillo/cli
- CLI documentation: https://fillo.so/docs/cli
- React SDK: https://www.npmjs.com/package/@usefillo/react
- Framework-neutral DOM SDK: https://www.npmjs.com/package/@usefillo/dom
- Core schema package: https://www.npmjs.com/package/@usefillo/core
- Source repository: https://github.com/jacobfunch/fillo

Resolve the latest package version from npm at install time. The CLI supports login, preview-workspace bootstrap, project selection, safe form staging and publishing, key management, status checks, and installation of the canonical Fillo agent skill.

## Machine-readable context

- Concise agent index: https://fillo.so/llms.txt
- Full agent reference: https://fillo.so/llms-full.txt
- Agent skill: https://fillo.so/agents.md
- All documentation as Markdown: https://fillo.so/docs.md
- Security and data handling: https://fillo.so/docs/security.md
- Product and founder facts: https://fillo.so/about.md