Fabler x402 Tools

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

With no annotations provided, the description carries the full burden. It discloses that the tool is free and requires no payment or wallet, and notes that paid tools are not wired for MCP. However, it does not describe the output format, potential errors, rate limits, or other behavioral traits that would help an agent understand the tool's behavior.

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

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

The description is verbose and includes extraneous information about paid tools, GitHub commands, and the MCP endpoint configuration that is not directly relevant to the tool's purpose. This detracts from conciseness and front-loading the essential information.

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

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

Given that there are no annotations and no output schema, the description lacks details about the return format, pagination, or response structure. It provides sufficient high-level context for a simple list tool but is incomplete for an agent to fully understand what to expect from the invocation.

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

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

The input schema has zero parameters with 100% coverage, so the description adds meaning by specifying what is listed (x402 products and their prices). This is baseline for a parameterless tool.

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

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

The description clearly states the primary action: listing Fabler Labs' x402 products with per-call USDC prices on Base. It is specific and provides a verb-resource pair. However, it also mentions that this MCP endpoint exposes a free bounded secret-scan preview, which could be a different capability and muddies the clarity regarding the sibling tool 'fabler_scan_secrets_preview'.

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

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

The description offers some context about when to use this tool (free, no wallet required) and mentions alternatives (paid tools via HTTP). However, it does not clearly distinguish this tool from its sibling 'fabler_scan_secrets_preview' and provides no explicit guidance on when not to use it or when to prefer another tool.

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

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

No annotations exist, so description carries full burden. It states 'return only masked matches' and 'Free, no wallet or account required,' which are useful behavioral traits. However, it does not specify what happens if no credentials are found or what patterns are scanned, missing some transparency. Still, for a preview tool, it's largely sufficient.

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

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

Three sentences: purpose, constraint/pricing, and alternative. No filler, front-loaded with key info. Every sentence adds value.

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

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

Given simple tool with one parameter, no output schema, and no annotations, the description covers purpose, input limit, cost, and how to handle larger inputs. Complete for intended use.

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

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

Schema coverage is 100% with one parameter 'text' described as 'Text to inspect. Maximum 2,048 characters.' The description repeats the length constraint but adds 'Free, no wallet...' which is not about parameter semantics. No new parameter-level meaning beyond schema.

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

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

Description clearly states 'Scan up to 2,048 characters for common credential patterns and return only masked matches.' This specifies the action (scan), resource (text), and outcome (masked matches). The sibling tool 'fabler_list_products' is unrelated, so no ambiguity.

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

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

The description explicitly says 'Free, no wallet or account required,' indicating when to use this tool, and provides an alternative: 'For larger inputs, use the $0.005 full scanner through the wallet-capable client: npx -y github:fablerlabs/x402-tools.' This gives clear when-to-use and when-not-to-use guidance.

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