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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description is not required to re-state that. It adds genuinely useful behavior beyond annotations: it discloses which data classes are returned (parameter mapping, postback settings/URLs) and a security-relevant fact — the API key is never returned, with has_api_key as the indicator.

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, front-loaded with the primary payload (what a traffic source record contains) and followed by the notable exception (API key withheld). The parenthetical list is mildly dense but earns its place by previewing the mapping content.

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 no output schema, the description carries the return-value burden and does it reasonably: it enumerates the main sections returned and flags a security exception. It stops short of describing the structure or field-level detail of the mapping, but for a single-resource lookup this is close to sufficient.

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?

There is only one parameter, id, and the schema documents it at 100% coverage, so the baseline is 3. The description's mention of 'source_id, zone_id, cost, sub1' refers to the returned parameter mapping, not the input id, so it adds no meaning to the parameter itself.

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?

Names a specific verb and resource and adds scope qualifiers: 'One traffic source with its parameter mapping ..., postback settings and postback URLs.' The singular 'One' implicitly separates it from list_traffic_sources, but no sibling is named explicitly.

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?

Usage is only implied by the shape of the tool (fetch a single source when you have an id). There is no explicit when-to-use statement, no mention of retrieving the id via list_traffic_sources, and no exclusions.

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