Register or update an image URL

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

With no annotations, the description carries the full burden. It discloses idempotency ('calling twice with the same key swaps the URL'), cost ('0 credits'), and update behavior. It could mention return expectations or error handling, but for a simple registration tool this is sufficient.

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 tightly written sentences, front-loaded with the core action. The example is compact and every clause (idempotent, cost, alternative) adds value. No 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?

For a simple two-parameter registration tool with no output schema, the description adequately covers purpose, usage, behavioral traits, and alternatives. Nothing critical is missing for an agent to invoke it correctly.

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?

The input schema already has 100% coverage with descriptions for both 'key' and 'url'. The description adds a concrete example of the key mapping, which reinforces but doesn't significantly extend the schema. Baseline 3 is appropriate.

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 clearly states the action: 'Bind a direct image URL to a stable key' with a concrete example. It distinguishes from sibling generate_image by noting when to use that alternative. The title also reinforces 'Register or update an image URL'.

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?

Provides explicit guidance on when to use this tool: for direct image URLs, and explicitly says 'For AI-generated images use generate_image instead.' Also notes idempotent behavior and zero cost, which helps decide if re-registration is safe.

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