Fallback MCP server

Fallback

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       find the route forward

Fallback

Tiny paid recovery and decision utilities for autonomous agents.

When an agent gets stuck, Fallback helps it find the next safe move without wasting a large reasoning loop.

sourceroute Where should I look? ($0.02)\ errorroute Why did this fail? ($0.002)\ requestrepair Can I safely fix the request? ($0.005)\ stopsearch Is another search worth it? ($0.003)

Use Fallback

Pay-per-call tools that help AI agents find sources, diagnose failures, repair requests, and decide when to stop searching. Fallback gives autonomous agents small, deterministic utilities for the moments where automation gets stuck: finding the right source, diagnosing a failed request, repairing a request from available evidence, and deciding whether another search or paid retrieval is worth the cost.

Hosted service

MCP endpoint: https://fallback.factrail.online/mcp\ HTTP API base: https://fallback.factrail.online\ Payment: x402 V2 pay-per-call. Check each live challenge for network, asset, amount, and recipient.\ Agent skill: skill.md\ OpenAPI: openapi.json\ Network: Base mainnet, canonical USDC\ Release: v0.1.0-beta.1

Tools

• sourceroute ($0.02): Where should I look?** Find likely authoritative or machine-readable sources.
• errorroute ($0.002): Why did my call fail?** Classify a failed request and recommend a bounded next action.
• requestrepair ($0.005): Can I safely fix the request?** Propose the smallest change supported by caller-supplied evidence.
• stopsearch ($0.003): Is further searching worth it?** Decide whether more bounded search effort is justified by the evidence and remaining cost.

These tools do not replace agent reasoning, and stop_search never proves universal absence.

When an agent should use this

Use sourceroute when an agent knows what it needs and which publisher (a domain or start URL), but not how** to get it in machine-readable form: an API, OpenAPI spec, bulk download, dataset or feed.

• Good fit: "Get the latest population dataset from Eurostat", "Find a JSON/CSV route for this agency's statistics", before the agent starts browsing page by page.
• Not a fit: general web research, answering a factual question, or verifying a fact (for source-backed facts, see FACTRAIL MCP).

How to read the result:

• status: routesfound: try routes in order. score is a deterministic ranking, not** a probability or confidence.
• status: nosuitableroutefound: nothing suitable within the checked scope (see checked.directprobes). This is not evidence that no route exists. The agent should look elsewhere (another host, the publisher's open-data portal), not conclude "there is no API".
• Always read limitations. It says, for example, whether external search was unavailable or candidate inspection was capped.

Limits per call: at most 8 direct HTTP requests, 12 s total, 1 MiB per response, and at most 1 external search request. No LLM inference. The hosted beta currently runs deterministic discovery only (no search provider configured).

Access: hosted MCP https://fallback.factrail.online/mcp (Streamable HTTP) or the HTTP tool routes, x402 pay-per-call (each challenge declares its payment network and amount; no account or API key). To try it without payment, self-host with PAYMENT_MODE=disabled (see Local development). Machine-readable summary: llms.txt. More detail: Using Fallback with agents.

Shortened. The full README is on GitHub.