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

The description adds substantial behavior beyond the readOnlyHint annotation: opt-in visibility, not-found behavior, paid vs. free transcript handling, price return, and the payment follow-up. This is exactly the kind of contextual behavior an agent needs to manage user expectations and next actions.

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, all necessary, with the core action and identifier source first. There is no filler or repetition of schema details; the payment and opt-in caveats are delivered efficiently.

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 single-sermon fetch with no output schema, the description covers the important return cases: metadata, transcript, price, and not-found. It also explains the permission model and the payment pathway, making the tool's behavior predictable for an agent.

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?

Input schema coverage is 100%, so the schema already documents both parameters. The description adds only a small amount of context ('optionally' and the payment workflow) but does not materially extend parameter meaning beyond what the schema states.

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 uses a specific verb ('Fetch') and names the exact resource ('full metadata and optionally the transcript for ONE sermon by its id'). It clearly positions the tool as a single-item lookup rather than a search, distinguishing it from siblings like search_sermons.

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 explains that the id is 'typically a sermon_id returned by search_sermons', which gives the agent a clear prerequisite and data source. It also routes paid-transcript use to pay_with_x402. However, it does not explicitly state when to avoid this tool in favor of a search or other sermon-related siblings.

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