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FareDice

by com.faredice
OverviewDiscussionsAdmin

Change one stop of a FareDice trip

swap_stop
Read-onlyIdempotent

Other places for one stop of a FareDice trip on the same days, keeping the rest of the trip: each with how much the trip's flights change and its link, cheapest first. With city, that change made: the new trip, as get_trip returns it. Places already in the trip, and countries it already visits or (with the link's passports) needs a visa for, are left out. 20 calls a day per caller (UTC) of find_trips, get_trip, swap_stop and edit_trip are free; after that each costs US$0.01, paid with x402 (USDC on Base). nonstop_fares and nonstop_from are always free.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "link": "<link>",
      "stop": "<stop>"
    },
    "name": "swap_stop"
  }
}

Input Schema

NameRequiredDescriptionDefault
cityNoA place from the list (its name or IATA city code) to put in that stop's place. Leave it out for the list.
linkYesA FareDice trip link, as find_trips returns it (https://faredice.com/trip?l=... or /sea/trip?l=...).
stopYesWhich stop to change: 1 is where the first flight lands, 2 the next, and so on.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A3.9/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (readOnly/idempotent/non-destructive/closed-world), the description discloses real behavior: results are ordered cheapest first, each item carries the flight-price delta and a link, and places already in the trip or blocked by visa/visited-country rules are excluded. It also discloses the rate limit (20 free calls/day per caller UTC) and the x402/USDC-on-Base cost after that, which is exactly the kind of operational context annotations cannot carry.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three dense sentences, front-loaded with the core behavior and followed by filtering rules and cost. Every sentence carries information, but the telegraphic first sentence ("Other places for one stop of a FareDice trip on the same days") costs parsing effort, and the pricing sentence enumerates tools that are only tangentially relevant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description does the work of describing both return shapes (cheapest-first list with price delta and link; or the substituted trip in get_trip form). The only residual ambiguity is whether the "change made" persists or is a hypothetical — an agent might want that stated explicitly, though the readOnly annotation resolves it.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and all three parameters are already documented (city as name or IATA city code, link format, 1-14 stop index). The description adds only the mode switch implicit in city, and otherwise restates the schema; baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states the specific resource (one stop of a FareDice trip) and the two modes of operation: without city it lists alternative places for that stop, and with city it produces the substituted trip. It is specific and distinguishable from a plain read, but it never names a sibling (e.g. edit_trip) as the contrasting alternative, leaving the boundary slightly implicit.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Useful in-tool guidance is present: "Leave it out for the list" and "With city, that change made" tell the agent when each mode applies. However, there is no guidance on when to choose swap_stop over edit_trip or find_trips; those names appear only in the pricing sentence, so sibling selection is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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