upload_imageStore a picture (PNG, JPEG, GIF or WEBP, up to 25 MB, base64-encoded) and get its "src" for an image block or a slide background. Big pictures are scaled down to 2560 px.
| Name | Required | Description | Default |
|---|---|---|---|
| data_base64 | Yes | The file, base64 (a data: URL prefix is allowed). |
| Name | Required | Description | Default |
|---|---|---|---|
| h | No | ||
| w | No | ||
| src | Yes | Use it as "src" of an image block or background. | |
| url | No |
Changes observed during successful MCP inspections.
Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "h": {
+ "type": "integer"
+ },
+ "src": {
+ "description": "Use it as \"src\" of an image block or background.",
+ "type": "string"
+ },
+ "url": {
+ "type": "string"
+ },
+ "w": {
+ "type": "integer"
+ }
+ },
+ "required": [
+ "src"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only declare this is a non-read-only, non-destructive, closed-world write. The description goes beyond them meaningfully: accepted formats, a 25 MB ceiling, base64/data-URL encoding, and the automatic downscale to 2560 px — the scaling behavior in particular is non-obvious and worth disclosing. It stops short of stating auth or any side effects of re-uploading.
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 tight sentences with zero filler. The core action and return value come first, and the constraints (formats, size, scaling) follow in a compact clause. Every clause carries information.
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?
An output schema exists, so return value structure needn't be spelled out, and the description still names the key output ('src'). Combined with format, size, encoding and scaling details, the definition is nearly complete; only permission/auth expectations are absent, which is minor for this tool.
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?
With one parameter at 100% schema coverage, the baseline would be 3, but the description adds real constraints the schema omits: the allowed formats (PNG/JPEG/GIF/WEBP) and the 25 MB size limit that bound valid input. That is genuine meaning beyond 'the file, base64'.
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 ('Store a picture') plus the concrete payoff ('get its "src" for an image block or a slide background'). No sibling does image upload, so omission of explicit differentiation is harmless. An agent immediately knows what this does and what it produces.
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?
Implies usage by naming the downstream consumers (image block, slide background), which gives the agent a reasonable sense of when it applies. However, it states no prerequisites, no exclusions, and no alternatives, since none of the siblings compete directly. Adequate but not explicit guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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