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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds genuine context beyond that: the channel/ChannelOAuthId is resolved internally, isoCountry falls back to the selected channel country, and there is an explicit warning not to invent supplier IDs. It does not disclose pagination, caching, or failure behavior for an open-world call.

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?

Purpose, usage and input/output are front-loaded and useful, but the block is padded with catalog metadata that adds no invocation value (ownerAgent, supportingAgents, Domain, Entity, Operation, Scope, 'Search terms: sources get'). The opening sentence about being 'an explicit tool with a fixed endpoint' restates the tool name rather than informing the caller.

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 description needn't enumerate return fields, yet it still summarizes them (Id, Name, BaseUrl, Site, publication permissions, HasAutoOrder, AutoOrderingFee), and it covers the input fallback and the ID-validity warning. The one real gap is that it never explains how it relates to its three sibling sources tools, which is the most likely source of mis-selection.

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%, so the baseline is 3, and the description earns above that by giving the actual fallback rule for isoCountry ('if not sent, use the selected channel country') rather than just restating the type. It also frames channelOAuthId as the channel selector resolved internally, reinforcing the schema's own note that it comes from hgr_list_channels.

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 names a concrete verb and resource ('Lists supplier/source marketplaces available to the user and the current channel') and scopes it to the current store, so the agent knows what it returns. However, it never differentiates itself from the near-identical siblings hgr_get_sources, hgr_get_sources_getpublic and hgr_get_sources_goout; 'Dedicated HGRApi tool for GET api/Sources/Get' merely restates the endpoint and does no discriminating work.

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 'Use when' block gives four concrete scenarios (building supplier selectors, mapping sourceId to names, resolving suppliers for catalog search, verifying publication/Auto Ordering support) which is clear positive guidance. It supplies no exclusions or 'use X instead' routing, which matters given four similarly named sources tools in the sibling list.

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