The full upstream README, mirrored here for reference. Install config, tool schemas, adoption signals, and an original overview live on the Stringer Grounded Synthesizer listing page.
This is a runnable reference implementation of the Stringer Grounded Synthesizer, a research
service that returns extractive quotations with citations from verified public sources and
refuses a topic it cannot ground. It mirrors the caller-observable surface of the hosted
service at synthesis.getstringer.app and holds nothing back that a caller can see.
The boundary rule is the one stated in the worker header: a behaviour belongs here when an unauthenticated caller can observe it from outside. The bearer-gated admin stats route, the Durable Object funnel counters, the caller hashing, and the provider cost rate card stay out.
Node.js 20 or newer. The Worker is dependency-free and runs with no API keys and no external state, because the default research provider is a fixture-backed stub. That is the point: a stranger can clone the tree and watch the grounding and the refusal end to end without holding a single paid key.
To run it as a Worker locally, use Wrangler 4 (npx wrangler dev). No secret setup is
required; the free allowance is held in process for the reference and is documented as such
in wrangler.toml.
https://synthesis.getstringer.app/mcpsynthesize_intelligencePOST https://synthesis.getstringer.app/v1/synthesizePOST https://synthesis.getstringer.app/v1/execute/.well-known/mcp.json, /server.json, /llms.txt, /llms-full.txt, /robots.txt, /sitemap.xmlThe first three calls are free, total, with no signup and no claim header. The allowance does
not reset. After that, a brief synthesis costs USD 0.10 and a deep synthesis costs USD 0.25,
both paid through x402 v2 USDC on Base (eip155:8453). An unpaid call after the allowance is
exhausted returns HTTP 402 with the accepted payment requirement in PAYMENT-REQUIRED and
the tier price in X-402-Price-USD.
GROUNDED: the quotation checks passed.REFUSED_UNVERIFIED_CLAIMS: fewer than the required verified sources, or a quote failed
verbatim verification.SOURCE_EXTRACTION_FAILED: a named source could not be fetched or extracted.The refusal is the product's whole claim. The test harness observes the grounded case and the refusal case red before making each green, so neither path can pass on a test that has never failed.
The research provider is an injectable seam. synthesizeGroundedReport takes a provider
argument, and the fetch handler reads env.researchProvider. The default is
createFixtureProvider(), which searches a fixed corpus of three source documents and never
makes a network call.
A real provider implements the same two methods:
Wire one in by exporting it on the Worker environment, for example with an Exa search key and a Firecrawl scrape key held as Worker secrets. The reference never hard-codes a provider's unit cost and never names the hosted service's margin internals; the seam is the only thing a reader needs to change.
Free responses carry X-Stringer-Access-Tier: free and X-Stringer-Free-Remaining. The
fourth call returns HTTP 402. See openapi.json and RECIPES.md for the full flow.
Streamable HTTP at https://synthesis.getstringer.app/mcp. Clients must send both
application/json and text/event-stream in Accept. The server implements initialize,
ping, tools/list, and tools/call for synthesize_intelligence.
MIT. See LICENSE.