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

Annotations already declare readOnly, idempotent, non-destructive behavior, so the bar is lower, yet the description adds a genuinely useful trait: 'The server returns URLs, not image bytes,' which prevents an agent from expecting binary content. It also compensates for the absent output schema by listing returned fields. It does not mention not-found/error behavior, so not a 5.

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, zero filler, front-loaded with the action and scope before the caveat about URL vs bytes. Every clause carries 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?

With no output schema, the field enumeration is essential and present, and the URL-not-bytes caveat closes the main expectation gap. Only error/not-found behavior is unaddressed, which is minor for a read-only lookup.

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?

Only one parameter and schema description coverage is 0%, so the schema contributes nothing about image_id. The description only says the lookup is 'by id,' conveying that it is an identifier but not its type, format, or provenance. Partial compensation, minimum-viable.

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 ('Get one photograph by id') and enumerates exactly which fields come back (title, photographer, capture date, place, subjects, rights, IIIF manifest, image_url). An agent can distinguish this single-record fetch from the numerous search_* and list_* siblings without opening either schema.

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 is only implied: retrieve one photograph by its id. There is no explicit when-to-use guidance, no mention of when to prefer search_images instead, and no statement about what happens for an unknown id. Adequate but leaves routing to inference.

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