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Glama

FabTally Guard

by io.github.zvmzaretsky

Verify an x402 endpoint before paying (paid $0.002)

x402_preflight

PAID $0.002 (x402, USDC on Base). Verify another x402 endpoint BEFORE paying it: does an unpaid call return a valid x402 v2 402 challenge? do the quoted amount/asset/network/payTo match the site's /.well-known/x402? is TLS valid, host reachable, openapi present? Returns pass/fail + per-check reasons + the parsed price you would pay. Args: url. Without payment returns the x402 challenge; pass x_payment to settle.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesThe x402 endpoint URL to verify, e.g. https://example.com/v1/thing.
x_paymentNox402 payment payload (base64) for this PAID check. If supplied it is forwarded as the X-PAYMENT header to settle the call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. First observed

TDQS

A4.6/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden and does so thoroughly. It explicitly discloses the $0.002 cost, the checks performed, the return format (pass/fail, reasons, parsed price), and the distinct behavior with and without x_payment. No destructive or hidden side effects are omitted.

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

Conciseness5/5

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

The description is compact yet dense, using three sentences to cover payment, purpose, checks, returns, and parameters. It front-loads the paid nature and starts with a clear action verb. Every sentence contributes essential information without fluff.

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?

Given the complexity of the tool and the lack of an output schema, the description covers most necessary context: purpose, usage flow, return values, and payment. It does not mention error handling or edge cases like network timeouts, but the included details are sufficient for typical use.

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

Parameters4/5

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

Schema description coverage is 100%, so the baseline is 3. The description adds meaningful behavior context for x_payment, explaining that omitting it yields a challenge and supplying it settles the call. This elevates the score above baseline, though the url parameter is already well-described in the schema.

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

Purpose5/5

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

The description clearly states the tool verifies an x402 endpoint before payment, with specific checks enumerated (challenge validity, price match, TLS, host reachability, OpenAPI presence). It distinguishes itself from siblings like url_read by focusing on x402-specific verification rather than generic URL reading.

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

Usage Guidelines4/5

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

The description clearly indicates when to use the tool: 'Verify another x402 endpoint BEFORE paying it.' It also explains the two usage modes: omit x_payment to get a challenge, or pass x_payment to settle. However, it does not explicitly name alternatives or state when not to use it, so it falls short of a 5.

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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TDQS

A4.6/5.0
Disambiguation5/5

Each tool targets a clearly distinct function: package vetting, JSON repair, URL fetching, and x402 endpoint verification. There is no overlap in intent or output, making selection unambiguous.

Naming Consistency5/5

All tool names follow a consistent snake_case object_action pattern (deps_check, json_repair, url_read, x402_preflight). This maintains uniformity and predictability across the set.

Tool Count5/5

With exactly four tools, the server is well-scoped and every tool earns its place. There is no bloat or trivial filler, and the count falls squarely within the ideal 3-15 range.

Completeness4/5

Each tool is functionally complete for its individual purpose, but the set lacks batch operations or a way to manage/retrieve prior checks. These are minor gaps that agents can work around with scripting or external state.

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