kovidgoyal/kitty · warning · ErrNoLexer

No lexer available for this format

Error message

No lexer available for this format

What it means

ErrNoLexer is returned by HighlightFile (and the highlight API) in tools/highlight when no chroma lexer can be resolved for the given file/format. The API uses chroma to syntax-highlight text; it first resolves a lexer by filename or format name (honoring SyntaxAliases() and TextForPath()); if chroma has no match, this sentinel error is returned so callers can fall back to plain, unhighlighted output.

Solutions

1. Handle ErrNoLexer explicitly and fall back to plain text rendering (errors.Is(err, highlight.ErrNoLexer))
2. Pass an explicit lexer/format (or add an entry to SyntaxAliases) so resolution succeeds
3. Verify the format string matches a chroma lexer name (see chroma's lexers registry)

Example fix

// before
text, err := highlight.HighlightFile(f, ..., srd)
if err != nil { return err } // unknown extension aborts preview

// after
text, err := highlight.HighlightFile(f, ..., srd)
if errors.Is(err, highlight.ErrNoLexer) {
    text, err = plainFallback(f) // render without highlighting
}
if err != nil { return err }

// pre-check lexer availability before highlighting
import "github.com/alecthomas/chroma/v2/lexers"

func hasLexer(path, format string, aliases map[string]string) bool {
    if a, ok := aliases[format]; ok { format = a }
    if format != "" && lexers.Get(format) != nil { return true }
    return lexers.Match(path) != nil
}

func isNoLexer(err error) bool {
    return errors.Is(err, highlight.ErrNoLexer)
}

text, err := highlight.HighlightFile(...)
if errors.Is(err, highlight.ErrNoLexer) {
    text = plainRender(...)  // graceful degradation
    err = nil
}

When it happens

Trigger: Calling HighlightFile with a file whose extension/first-line yields no chroma lexer, or a format string that isn't a registered lexer name and isn't covered by the StyleResolveData's syntax aliases; e.g. highlighting a file with an unknown extension like .xyz123.

Common situations: Previewing or echoing files with exotic or extensionless names in kitten tools (e.g. `kitten icat`-adjacent previews, `kitten diff` on unusual files); custom format strings that don't map to chroma lexer names; a syntax alias map missing an entry for a newly supported format.

Related errors

• Canceled by user
• Execute command
• No cache found and max cache age is negative
• Too much piped data
• Aborted by user!

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/d9d0a8cfaeb2bfe9. Report an issue: GitHub.

Appendix: source

Thrown at tools/highlight/api.go:13

package highlight

import (
	"errors"
	"fmt"

	"github.com/alecthomas/chroma/v2"
	"github.com/kovidgoyal/kitty/tools/utils"
)

var _ = fmt.Print

var ErrNoLexer = errors.New("No lexer available for this format")

type StyleResolveData interface {
	StyleName() string
	UseLightColors() bool
	SyntaxAliases() map[string]string
	TextForPath(string) (string, error)
}

type Highlighter interface {
	HighlightFile(path string, srd StyleResolveData) (highlighted_string string, err error)
	Sanitize(string) string
}

func NewHighlighter(sanitize func(string) string) Highlighter {
	if sanitize == nil {
		sanitize = func(text string) string { return utils.ReplaceControlCodes(text, "    ", "\n") }
	}
	return &highlighter{sanitize: sanitize, tokens_map: make(map[string][]chroma.Token)}

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