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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the bar is lower, yet the description adds domain-specific behavioral context beyond them: it never signs, settles, or interprets a payment, and it points to where payment/job state actually lives. That is more than restating the hints and usefully scopes what the tool will and won't do.

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?

Two sentences, zero filler: the first front-loads what is returned, the second immediately bounds scope and safety. Every clause carries information an agent would otherwise have to infer.

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?

With an output schema present, the return shape need not be explained, and the description still summarizes it. Combined with rich annotations and zero required inputs, an agent has everything needed to select and call this tool correctly; the explicit statement that payments are handled elsewhere closes the main ambiguity.

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 tool takes zero parameters, so the baseline is 4 and there is no parameter semantics to document. The description correctly names the discovery categories returned rather than inventing input concepts that don't exist.

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?

States a specific verb and resource ('Discover Sourcey's enabled paid agent services and canonical HTTP resources') and enumerates exactly what the payload contains (request/response contracts, price floor, policy links, x402 discovery). It is unmistakably a discovery tool, but it never explicitly differentiates itself from siblings like search_offers or compare_offers, which also deal with offers/pricing.

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 second sentence draws a clear boundary: payment execution and durable job status live on the product HTTP API, not here. That is genuine when-not guidance for an agent deciding whether this tool can resolve a payment question. It stops short of routing to a specific sibling tool for offer comparison or searching.

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