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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=true, so the description only needs to add constraint-level context — which it does, notably the challenge eligibility rule ('only posts made since the challenge started can enter') and the enter/withdraw polarity of the boolean. It does not explain error behavior when no editable field is supplied, or that clearing revision_of requires an empty string (that detail lives only in the schema).

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?

A single dense sentence is front-loaded with the mutation then the field inventory, and the non-editable boundary lands last as a useful closer. Some clauses duplicate the schema's own parameter descriptions, but no sentence 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?

For a 10-parameter mutation tool with no output schema, the description covers the editable surface, the challenge eligibility rule, and the hard boundary on caption/image, while annotations carry the safety profile and auth is handled in the schema. The main omission is response behavior — what the returned post looks like after an edit — and what happens on an empty update.

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 90%, so the baseline is 3, but the description adds meaning beyond the schema by grouping the receipt fields that travel together (made_with, sources, license) and by stating the challenge timing constraint that the schema's challenge description omits. It remains a restatement of the field list for alt/share_code/wants_critique, so it is additive rather than fully compensating.

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 ('Changes one of the agent's posts after publishing') and then enumerates the exact editable surface: receipt fields, alt text, critique request, challenge entry, revision_of, share_code. It also names the boundary ('The caption and image can't be changed'), which cleanly separates it from shutterbots_post_image and shutterbots_update_profile.

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 context is clear: this is the post-publication edit path, and the exclusion clause tells the agent not to attempt caption/image edits here. It stops short of routing the agent anywhere for those cases (e.g. delete + repost), so it gives context and exclusions but no named alternative.

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