pbakaus/impeccable · error

embed-prompt: prompt too long for a JPEG segment

Error message

embed-prompt: prompt too long for a JPEG segment

What it means

JPEG embedding uses a COM marker segment whose length field is 16-bit (max 0xffff bytes). If keyword + NUL + prompt exceeds the segment capacity, the CLI refuses and exits 1 rather than producing a corrupt JPEG.

Source

Thrown at crates/context/src/embed_prompt.rs:321

                o.extend_from_slice(&body);
                o.extend_from_slice(&text_chunk);
                o.extend_from_slice(&png_chunk(b"IEND", &[]));
                o
            } else {
                let mut o = buf[..iend].to_vec();
                o.extend_from_slice(&text_chunk);
                o.extend_from_slice(&buf[iend..]);
                o
            };
            let _ = std::fs::write(&file_abs, out);
            io.out(&format!("EMBEDDED: {} (png tEXt, {} chars)\n", file, plen));
            0
        } else if jpeg {
            let mut seg = KEYWORD.to_vec();
            seg.push(0);
            seg.extend_from_slice(prompt.as_bytes());
            if seg.len() + 2 > 0xffff {
                io.err("embed-prompt: prompt too long for a JPEG segment\n");
                return 1;
            }
            let mut com = vec![0xff, 0xfe];
            com.extend_from_slice(&((seg.len() + 2) as u16).to_be_bytes());
            com.extend_from_slice(&seg);
            let mut out = buf[..2].to_vec();
            out.extend_from_slice(&com);
            out.extend_from_slice(&buf[2..]);
            let _ = std::fs::write(&file_abs, out);
            io.out(&format!("EMBEDDED: {} (jpeg COM, {} chars)\n", file, plen));
            0
        } else {
            let mut m = Map::new();
            m.insert("prompt".into(), Value::String(prompt));
            m.insert("createdAt".into(), Value::String(iso_now()));
            let _ = std::fs::write(&sidecar_abs, json_pretty(&Value::Object(m)));
            io.out(&format!("EMBEDDED: {} (sidecar fallback for this format)\n", sidecar));
            0

View on GitHub (pinned to 2bc2879276)

Solutions

1. Shorten the prompt text before embedding into a JPEG.
2. Embed into PNG instead (PNG tEXt has no 64KB segment limit) if the long prompt is required.
3. Store the full prompt in a sidecar file and embed only a short reference.

Example fix

// before
impeccable embed-prompt --image photo.jpg --prompt "$(cat huge-transcript.txt)"
// after
head -c 60000 huge-transcript.txt > short.txt
impeccable embed-prompt --image photo.jpg --prompt "$(cat short.txt)"

const KEYWORD = 'prompt'; if (Buffer.byteLength(KEYWORD) + 1 + Buffer.byteLength(prompt) + 2 > 0xffff) { throw new Error('prompt too long for JPEG COM segment'); }

try { embedPrompt(jpeg, prompt); } catch (e) { if (/too long/.test(e.message)) prompt = prompt.slice(0, 60000); }

When it happens

Trigger: Running `embed-prompt --image photo.jpg --prompt <very long text>` where the prompt (plus 1-byte keyword and separator) makes the COM segment exceed 65535 bytes.

Common situations: Embedding entire system-prompt transcripts or very long generation configs into JPEGs; PNG has no such limit but JPEG does.

Understand the failure class

Background: payload too large / request exceeds maximum size: why libraries cap bytes and how to fix oversize payloads — this error's family across 50 libraries.

Related errors

• embed-prompt: no embedded prompt found
• Update failed: Aborted.
• concept-seed: --candidate-count must be an integer from 5 to
• Unknown ignore-rule flag: ${arg}
• Pass a rule id, e.g. ${IMPECCABLE_COMMAND} hooks ignore-rule

AI-assisted analysis of pbakaus/impeccable@2bc2879276 (2026-09-08). Data as JSON: /api/errors/a2f8bfe3ab627d8b. Report an issue: GitHub.