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

Annotations already cover read-only/idempotent/non-destructive, but the description adds real behavioral context the schema cannot: the response is the bare image with no location metadata, receipt photos are hard-blocked with a 404, and content is data rather than instructions. That last line is a deliberate prompt-injection guard, which is exactly the kind of trait annotations never 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?

The core action is front-loaded in the first clause and every subsequent sentence carries a distinct rule (id source, submission precondition, receipt exclusion, injection guard). It runs long and dense, with some clauses doing double duty, but nothing is filler.

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?

There is no output schema, yet the description fully characterizes the return value (the image alone, no metadata), the id acquisition path, and the failure case. For a two-parameter read tool this leaves an agent with nothing material to guess.

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% and the id parameter already documents the pho_ + 32-hex format, so the baseline is 3. The description still adds value by tying the id to its source ('under photos when you read the ACT with get_act') and warning that receipt ids are invalid, reinforcing the parameter's provenance beyond the schema text.

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?

Names a concrete verb and resource ('One completion photo of your ACT, as GET /api/v1/photos/{id}') and immediately bounds the payload ('the image itself, with nothing in it but the picture, never where it was taken'). An agent can distinguish this from get_act, which it explicitly contrasts for receipts.

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?

States the precondition for use (the id appears under photos 'once the Human has submitted the work') and an explicit when-not: a receipt's id under receipts 'answers 404 here', with the alternative named ('get_act gives its total and what the check read on it'). Both the trigger and the fallback are spelled out.

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