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

Annotations provide only a title, so the description carries the full burden. It discloses streaming (no memory buffering), integrity hash, resume capability, and filename resolution order. It does not mention auth needs, error handling, or overwrite behavior, but the key behavioral traits are covered.

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 with zero fluff. The first sentence front-loads the core function and key features; the second provides usage guidance and filename resolution. Every clause earns its place.

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 tool with 5 params and no output schema, the description is nearly complete. It explains streaming, integrity, resume, filename rules, and intended use cases. It omits what the agent receives back (e.g., file path or status) and does not mention network failure handling, but these are minor given the richness already present.

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 baseline is 3. The description adds value by explaining filename resolution precedence (explicit → Content-Disposition → URL tail), which clarifies the 'filename' parameter beyond the schema. Other params like 'resume' and 'use_proxy' are adequately described in the schema and need no extra explanation.

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 states a specific verb ('download'), a clear resource (file over HTTP(S)), and distinct behaviors (streaming to disk, SHA-256 hash, resume). It differentiates itself from siblings by explicitly contrasting with reading text content, making it unambiguous which tool to choose.

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 it ('Use for binaries, archives, datasets, documents') and implicitly when not ('not its text content read'). It provides a clear use-case boundary but does not name a specific alternative tool like 'fetch', so it stops short of full explicit routing.

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