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

Beyond the readOnlyHint and destructiveHint annotations, the description explicitly says 'No backend call; safe to call any time', which is a concrete behavioral guarantee. It also discloses limitations by stating it covers 'what this surface deliberately will not do', adding transparency not present in structured metadata.

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 front-loaded with the key instruction ('read it before...') and is information-dense with no filler. However, it is a single long, run-on sentence that packs many topics together, so slightly better structuring would improve scannability.

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?

For a zero-parameter, read-only reference tool with no output schema, the description is remarkably complete: it states the purpose, enumerates covered topics, names the dependent sibling tools, clarifies cost/behavior, and explicitly notes non-goals. An agent has enough context to decide when and why to call it.

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 has zero parameters, so the baseline of 4 applies. There is no parameter semantics to add, and the description appropriately focuses on the reference content rather than parameter details.

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 identifies the tool as the reference for configuring sourcing lanes and enumerates its full scope (lanes, config fields, gates, cadence, costs, non-goals). It distinguishes itself from sibling operational tools by explicitly naming gtm_configure_source / gtm_set_source / gtm_run_source as calls that should follow reading this reference.

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?

It gives an explicit usage directive: read it before your first configure/set/run source call. It also states that it has no backend call and is safe to call any time, which tells the agent when it is appropriate to invoke without side effects. This is strong guidance for a reference tool.

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