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

Annotations already indicate the write and non-idempotent nature. The description adds valuable context: the fetch is server-side, private networks are blocked, returns the data_source_id once preprocessing starts (indicating async), and the URL is fetched only once. These details go beyond annotations and set accurate expectations.

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 compact and well-structured: primary action first, then formats, security constraints, return value, and usage guideline. Every sentence contributes useful information without redundancy or padding.

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?

Given the tool's complexity (5 params, async behavior, security constraints) and the presence of an output schema, the description covers all key aspects: purpose, formats, limitations, return behavior, and when to use. Minor details like failure modes are left out but are likely covered by the output schema or are non-essential.

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 description coverage is 100%, so all parameters are already documented in the input schema. The description reinforces the 'url' behavior (public fetch, blocking) and 'format' hint but adds little new semantic value beyond schema. A baseline of 3 is appropriate when schema carries the load.

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 begins with a specific verb and resource ('Create a new data source'), explains the method ('fetching a public URL on the server side'), lists supported formats, and distinguishes from siblings by mentioning the 25 MB upload cap and the 'upload_data_source' alternative context. This clearly identifies what the tool does and sets it apart.

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 description explicitly states when to use this tool ('files larger than the 25 MB inline upload cap') and implicitly contrasts with the upload alternative. It also states a key limitation: private networks are blocked, implying those URLs should not be used. Though the sibling tool is not named, the guidance is clear and actionable.

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