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

With only readOnlyHint=false and openWorldHint=true in annotations, the description carries real weight: async background ingestion, per-type 501 behavior, prepaid billing rates with a 1-minute minimum, 402 on short balance, and required `write` scope. That is exactly the cost/auth/failure context annotations cannot express.

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?

Four tight sentences: action and endpoint first, then type support limits, then pricing/error behavior, then auth. No filler, and the highest-risk facts (cost, 501, 402) are front-loaded enough to be read before invoking.

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 mutating, externally-billed, no-output-schema tool, the definition covers cost, auth, async behavior, and error codes well. It is slightly incomplete on what the call actually returns (a source/ingestion handle?) and on how `idempotency_key` interacts with the background job, which matters for retries.

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 3 baseline applies to the parameter shapes themselves. The description still adds genuine meaning beyond the schema by declaring that two of the three `type` discriminators are non-functional today, which the schema presents as equally valid options.

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 (add) plus resource (source to a channel) and the side effect (begins background ingestion), and pins it to POST /v1/channels/{channelId}/sources. It does not distinguish itself from the sibling `add_sources` (plural), leaving an agent to guess which of the two to call.

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 constraints are stated as facts (only `type: video` is processed; `document`/`website` return 501), which effectively tells the agent what not to attempt. However there is no explicit routing guidance against the near-identical sibling `add_sources`, and no stated prerequisites beyond the `write` scope.

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