express_get_image

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

With no annotations supplied, the description carries the full behavioral burden and does so: it flags the write-side effect ('SIDE EFFECT: opens the chat if not already active (marks read)'), discloses that content is decrypted, and notes the resolution limitation. It also explains the return value (a file path you can then read/view), closing the main gap for a save-to-disk 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?

Three dense sentences with the action and output first, then input provenance, then limits, then the side effect. Every clause adds information an agent needs; nothing is redundant with the name or title.

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 two-parameter tool with no output schema, the description covers inputs, return value, capability limits, and the mutating side effect. Nothing material is missing for correct invocation.

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 description coverage is 0%, so the description must compensate, and it does: chatId is identified as the chat and syncId as the message identifier, with provenance pointing to express_read_chat / express_open_link outputs. Neither parameter's string format is elaborated, which keeps it short of a 5.

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+resource: fetching an image message's decrypted preview thumbnail and saving it to a local file. It also explicitly scopes the output ('this is a thumbnail, not full resolution'), which separates it from a full-resolution sibling like express_download_file without opening any 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?

Gives the prerequisite inputs and where to source them ('from express_read_chat / express_open_link output') and states the precondition 'Only images have previews'. It implies but never names express_download_file as the alternative for full-resolution retrieval, so the routing is clear but not fully explicit.

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