Fallback

Name: Fallback
Author: baronsigma

by baronsigmaversion 0.1.0-beta.1i★ –iRuns in the cloud

Registry nameio.github.baronsigma/fallback-agent-tools

Install

Overview

Description from the maker (original English)

Tiny paid recovery and decision utilities for autonomous agents.

PopNx MCP’s three pillars

These three are never merged into one score: opinions, measurements and popularity are different things.

User voiceiNo reviews yetReviews open together with accounts in a later step
Our basic checksi1 of 1 passedChecked from public information; code not scanned yet
UsageiNot measured yet★ –

What you can do with it

We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.

Connection: Runs in the cloud
Transport: Streamable HTTP
Category: Other

Install

Pick the AI app you use, then copy the settings.

Before you install

Basic checks: 1 of 1 passed
Runs on the maker’s server: what you ask it goes through their server.
The registry lists no key to fill in.

You need

Runs in the cloudNothing to install; it connects over the internet

Which app do you use?

ClaudeClaude CodeCursorVS CodeChatGPT

Pick your app above. We remember it, so next time the button says “Install in …”.

Works in Claude on the web, desktop and mobile:

Open Settings → Connectors
Press Add custom connector
Paste the address below and press Add
If it asks you to sign in, sign in with the maker

https://fallback.factrail.online/mcp

Run this in your terminal

claude mcp add --transport http fallback-agent-tools https://fallback.factrail.online/mcp

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

{
  "mcpServers": {
    "fallback-agent-tools": {
      "url": "https://fallback.factrail.online/mcp"
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "fallback-agent-tools": {
      "type": "http",
      "url": "https://fallback.factrail.online/mcp"
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

ChatGPT connects only to servers on the internet:

Open ChatGPT on the web → Settings → Connectors (Apps)
Press Create or Add (some plans need Developer mode under Advanced first)
Paste the address below, give it a name and save
If it asks you to sign in, sign in with the maker

https://fallback.factrail.online/mcp

Menu names can differ slightly by plan and over time.

Your choice stays on this device in a cookie; no account needed.

These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.

What it can do

We have not read this server’s tool list yet; we check endpoints in rotation.

Basic checksi

We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 6, 2026

✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account baronsigma, which owns the repo
… Not checked yet
Still maintained
We have not read this repo from GitHub yet
… Not checked yet
Has a licence
We have not read this repo from GitHub yet
… Not checked yet
Endpoint responds
Not checked yet; we check endpoints in rotation
… Not checked yet
Sign-in with OAuth
Not checked yet; we check endpoints in rotation
… Not checked yet
No hidden instructions in tool descriptions
Not checked yet; we read the tool list when we check the endpoint

Compared with others in Otheri

More stars than 0% of the other 32461 servers in this category
Published to the registry more recently than 57% of the other 32461 servers in this category
Basic checks equal to or better than 100% of the other 32461 servers in this category

Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.

Common questions

Is Fallback safe?

It passed 1 of 1 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.

What keys or codes does it need?

The registry does not list a required key, though some servers ask you to sign in on first use.

Does it run on my computer or in the cloud?

It runs in the maker’s cloud. Connect over the internet with nothing to install, but what you send passes through the maker’s servers.

Is it still maintained?

The GitHub repo last changed –, and the latest version (0.1.0-beta.1) reached the registry 31 days ago.

Which apps can use it?

Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. It connects by URL, so apps that accept remote MCP servers work too, such as ChatGPT in developer mode.

What can I use instead?

In the same category: Spec Driven Development, Remote Desktop Commander, dotnet-mcp

Alternatives

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README from the maker

Open the README

Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.

Fallback

  ______      _ _

| __| | | | | | __ _ | | | _ _| | | __|/ _ || | '_ \ / _ |/ __| |/ / | | | (_| || | |_) | (_| | (__| < |_| \__,_||_|_./ \,_|\___|_|\_\

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.

source_route Where should I look? ($0.02)\ error_route Why did this fail? ($0.002)\ request_repair Can I safely fix the request? ($0.005)\ stop_search 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

source_route ($0.02): Where should I look? Find likely authoritative or machine-readable sources.
error_route ($0.002): Why did my call fail? Classify a failed request and recommend a bounded next action.
request_repair ($0.005): Can I safely fix the request? Propose the smallest change supported by caller-supplied evidence.
stop_search ($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 source_route 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: routes_found: try routes in order. score is a deterministic ranking, not a probability or confidence.
status: no_suitable_route_found: nothing suitable within the checked scope (see checked.direct_probes). 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.

Fallback is publicly launched. See the current launch and distribution status, product rename impact audit, discovery/distribution readiness audit, and telemetry and 30-day KPI definitions.

When to use `error_route`

Use it after an HTTP, API, MCP, or tool request fails when the safe next action is unclear. It classifies supplied evidence and returns bounded retry guidance. Do not use it when recovery is already obvious or the task needs deeper domain reasoning; it does not execute requests or invent undocumented fixes.

Requirements

Current Node.js LTS (Node 24 at scaffold creation; supported engine is Node 22+)
npm

Local development

npm install

cp .env.example .env npm run generate npm run dev

The server exposes /, /healthz, /readyz, /catalog.json, /openapi.json, /llms.txt, /llms-full.txt, /skill.md, /.well-known/x402.json, /.well-known/mcp/server-card.json, and the Streamable HTTP MCP endpoint at /mcp. Both HTTP and MCP dispatch through the shared runtime handler registry. PAYMENT_MODE=disabled supports local development; paid deployments must explicitly select test or production and provide complete x402 configuration.

Verification

npm test

npm run typecheck npm run lint npm run benchmark:source-route npm run benchmark:error-route npm run verify:catalog npm run release:check

30-second start

Connect an x402-compatible agent to https://fallback.factrail.online/mcp, call the matching tool after a concrete failure or search decision, and approve only the network, token, recipient, and amount shown by its payment challenge. HTTP clients can use POST /v1/tools/{tool_id} on the hosted origin. See skill.md for examples and schemas.

Architecture

src/core/registry.ts is the one canonical tool registry. Every discovery surface and distribution artifact is derived from it. Each tool gets a directory under src/tools/ with a contract and handler; future tool tests and fixtures belong alongside the matching contract test/fixture directories. HTTP and MCP adapters must call the same tool handler. Payment middleware and marketplace integrations stay outside tool logic.

The service supports x402 V2 per-call payment without accounts or API keys. The server only receives payment at X402_PAY_TO; no receiving wallet private key is required. Paid startup fails closed if the required network, receiving address, facilitator URL, or production URL is missing or invalid. See deployment and payment setup.

Example

"goal": "Download the latest population dataset", "start_url": "https://ec.europa.eu/eurostat/", "preferred_formats": ["csv", "json"] }

Call POST /v1/tools/source_route with a goal and either start_url or domain. The result is limited to the checked scope; a missing result does not mean that no route exists. Direct site discovery runs without external search credentials. If Tavily or Brave is configured and direct discovery is insufficient, the tool can make at most one search request.

See PRODUCT, ARCHITECTURE, TOOL_ADMISSION, DISTRIBUTION, and RELEASE.

Related: FACTRAIL MCP

Fallback comes from the same author and design rule as FACTRAIL MCP: agent tools should report what they checked, not only what they found. FACTRAIL answers "what is established about this fact, and from which source?" by returning evidence envelopes with support levels, unresolved fields and receipts ("unknown is better than invented"). Fallback answers "where can I get this data?" ("absence is not proof of nonexistence"). The two are independent services with no code dependency, and you can use either one alone.

Fallback

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

What it can do

Basic checksi

Maker matches the repo

Still maintained

Has a licence

Endpoint responds

Sign-in with OAuth

No hidden instructions in tool descriptions

Compared with others in Otheri

Common questions

Alternatives

Spec Driven Development

Remote Desktop Commander

dotnet-mcp

README from the maker

Fallback

Fallback

Use Fallback

Hosted service

Tools

When an agent should use this

When to use error_route

Requirements

Local development

Verification

30-second start

Architecture

Example

Related: FACTRAIL MCP

When to use `error_route`