siyuan-note/siyuan · error

task list item marker can not be [ or ]

Error message

task list item marker can not be [ or ]

What it means

The single marker character cannot itself be '[' or ']'. Those characters are the checkbox delimiters in Markdown, so using them as the mark would produce ambiguous/unrenderable syntax like [[x]]; buildUpdatedTaskListItemBlockDOM rejects them explicitly.

Solutions

1. Pass the semantic mark ('x', ' ', or another non-bracket character) instead of a character sliced from the raw DOM/Markdown text
2. Parse the current state first (e.g. data-task / data-task-checked attributes or subtype) and toggle between 'x' and ' '
3. Validate before the call: if (marker === '[' || marker === ']') reject the request
4. Escape or sanitize user input used as a custom marker

Example fix

// before
const marker = rawText[1] === 'x' ? rawText[1] : rawText[0]; // may yield '[' or ']'
// after
const marker = isChecked ? 'x' : ' ';
if (marker === '[' || marker === ']') throw new Error('invalid marker');

if (marker === '[' || marker === ']') {
  throw new Error('marker cannot be a bracket; use x or space');
}

const isNonBracketMarker = (m) => m.length === 1 && !['[', ']'].includes(m);

try {
  await fetchPost('/api/block/updateTaskListItemMarker', { id, marker });
} catch (e) {
  if (String(e?.msg).includes('can not be [ or ]')) {
    return fetchPost('/api/block/updateTaskListItemMarker', { id, marker: 'x' }); // fall back to default mark
  }
  throw e;
}

When it happens

Trigger: Calling the marker update API with marker:'[' or marker:']' — typically from code that slices one character out of a raw "[x]" string at the wrong offset, or user-supplied input passed through unvalidated.

Common situations: String-parsing code doing marker = raw[0] on "[x]" yields '['; templating that substitutes a captured bracket; accidental passing of the literal bracket when toggling state.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• task list item marker length should be 1
• 106
• 199
• block is not a task list item
• block not found

AI-assisted analysis of siyuan-note/siyuan@9f775e8a12 (2026-09-19). Data as JSON: /api/errors/859d2e71d3ee0a67. Report an issue: GitHub.

Appendix: source

Thrown at kernel/api/block_op.go:64

		return "", errors.New("load tree failed: " + err.Error())
	}

	li := treenode.GetNodeInTree(tree, id)
	if li == nil {
		return "", errors.New("block not found")
	}

	if 3 != li.ListData.Typ {
		return "", errors.New("block is not a task list item")
	}

	if 1 != len(marker) {
		return "", errors.New("task list item marker length should be 1")
	}

	liMarker := marker[0]
	if '[' == liMarker || ']' == liMarker {
		return "", errors.New("task list item marker can not be [ or ]")
	}

	markerNode := li.ChildByType(ast.NodeTaskListItemMarker)
	if nil == markerNode {
		return "", errors.New("task list item marker not found")
	}

	markerNode.TaskListItemMarker = liMarker
	markerNode.TaskListItemChecked = ' ' != markerNode.TaskListItemMarker

	treenode.RefreshUpdated(li)

	return luteEngine.RenderNodeBlockDOM(li), nil
}

var updateTaskListItemMarker = contractHandler(apicontract.UpdateTaskListItemMarker, func(c *gin.Context, request apicontract.TaskListMarkerRequest) apicontract.Response[[]*apicontract.BlockTransaction] {
	ret := gulu.Ret.NewResult()

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