download_image

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

Annotations only flag readOnly=false, idempotent=false and openWorld=true; the description goes well beyond them by explaining the write-to-disk rationale, that existing files are never overwritten, that only FamilySearch URLs are fetched because the request carries the access token, and that content may be copyrighted or access-restricted. This is exactly the kind of context annotations cannot express, and it is consistent with idempotentHint=false.

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 short paragraphs, each front-loaded with its point: what it does, why the file is on disk, what URLs are permitted, and the copyright caveat. No sentence is filler; every one carries distinct information.

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 mutation-style tool with no output schema, the description covers side effects (file written, never overwritten), authorization (FamilySearch token scope) and legal caveats (copyright). It does not say what the tool returns on success, which is a minor gap given an agent may want confirmation of the written path.

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 both parameters (image_url, destination) are already fully documented with examples and constraints. The description adds no parameter-level syntax or format detail, so the baseline of 3 applies.

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 and resource — download a document image to a local file — with the intent (so it can be read) made explicit. It distinguishes itself by framing this as the terminal evidence step, though it only implicitly separates itself from siblings like get_image_links and get_film_image, which the input schema names as the URL sources.

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?

Clear context is given: this is the step that turns a citation into evidence, implying it follows a link-retrieval call, and the schema explicitly points at get_image_links/get_film_image as the URL origin. No explicit when-not or direct sibling comparison beyond that, so it stops short of a 5.

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