Optimise images

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

Annotations already declare destructiveHint=false and idempotentHint=true, but the description adds substantive context beyond them: new files are written to "<input folder>/optimized/" with originals untouched, re-runs skip unchanged files, there is a 45s execution ceiling after which a jobId is returned, and the allowed-directories line flags that no directories are currently configured. These are exactly the operational constraints an agent needs before invoking a write tool.

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 description is dense and front-loaded, leading with the default policy before enumerating variants and then the write/timeout behavior. It is on the long side and partially mirrors schema text (policies, resize semantics), but each sentence carries operational information rather than 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 15-parameter, nested-schema, no-output-schema tool, the description covers the essentials: output location, idempotency, timeout/job handoff, dry-run preview, and the fact that no directories are configured. Minor gaps remain – urlBase, response_format, pagination (limit/offset), and metadata handling are left entirely to the schema, which does document them adequately.

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 baseline is 3; the description earns an extra point by explaining how the parameters interact rather than restating them – per-image decisions, resizing respecting each image's own aspect ratio with no upscaling, widths producing srcset sizes, crop producing exact shapes. The policy tradeoffs are also given in prose with browser-compatibility context.

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 opens with a specific verb and resource ("Optimise images") plus a scope qualifier ("deciding per image"), then enumerates the policies it chooses among. An agent can immediately separate it from analyze_images (read-only analysis) and get_job (job polling), which the description names explicitly.

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?

It clearly states the default behavior (policy "auto"), when to pick alternatives ("avif" for smaller files with Safari 16.4+, "picture" for fallback markup, "keep" to preserve format), and when to use dryRun ("to preview decisions without encoding"). It also routes to get_job when the run exceeds 45s. It does not explicitly say when to prefer this over analyze_images, so it falls short of a full 5.

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