Bracket Tags: The Director's Language SUNO Doesn't Tell You About

Here's something SUNO's official documentation barely mentions: the Lyrics field isn't just for lyrics. It's a full director's language — a system of bracket tags, structural markers, and inline instructions that let you control arrangement, dynamics, vocal delivery, and instrumentation on a section-by-section basis.

Most users discover square brackets by accident. They type [Verse] because they saw it somewhere, and it works. But that's scratching the surface of a system that goes much deeper. There are three types of brackets, each with different behavior. There are per-section limits that nobody talks about. And in V5, there's a new colon syntax that opens up entirely new possibilities.

This is the complete guide to SUNO's bracket tag system — everything we've verified through testing, organized from basic to advanced.

The Three Bracket Types#

SUNO recognizes three distinct bracket syntaxes. Most people only know about square brackets. The other two are less documented but verified through community testing.

Square Brackets: [tag] — The Director's Commands

Square brackets are strong directives. They're the primary command system in the Lyrics field. When SUNO encounters a square bracket tag, it treats it as a high-priority instruction that should be followed as closely as possible.

[Verse 1]
[whispered]
[acoustic guitar only]
Late at night I hear you calling...

Square bracket tags work for:

• •Structure: [Verse], [Chorus], [Bridge], [Outro], [Intro]
• •Vocal delivery: [whispered], [belted], [rap], [spoken word]
• •Instrumentation: [piano solo], [guitar riff], [drums only]
• •Dynamics: [building intensity], [stripped back], [full band]
• •Effects: [reverb heavy], [distorted], [lo-fi]

Parentheses: (tag) — Soft Hints and Background

Parentheses are soft suggestions. They carry less weight than square brackets and are often interpreted as background elements, ad-libs, or secondary layers.

[Chorus]
I'm on fire tonight
(oh-oh, oh-oh)
Nothing's gonna stop me now
(yeah, yeah)

In this context, the parenthetical text becomes backing vocals or ad-libs rather than the main vocal line. This is one of the most useful tricks for creating layered vocal arrangements without any complex syntax.

Parentheses also work as soft style hints when placed at the start of a section:

[Verse 2]
(softly, with hesitation)
Maybe I was wrong to leave...

The key difference: square brackets demand, parentheses suggest. SUNO follows square brackets more strictly. Parentheses give the AI more room to interpret.

Curly Braces: {tag} — Emphasis and Repetition

Curly braces are the least documented bracket type. Community testing suggests they function as emphasis markers — signaling that the enclosed content should receive extra weight or repetition in the output.

[Chorus]
{I will not break}
I will not break
No, {I will not break}

In practice, content in curly braces often gets more vocal emphasis, slight repetition, or layered treatment. Results are less consistent than square brackets, so we recommend using them sparingly — they're a seasoning, not a main ingredient.

Reliability ranking: Square brackets (most reliable, ~90% compliance) > Parentheses (~70% compliance) > Curly braces (~50% compliance). Use square brackets as your primary tool and the others for nuance.

Per-Section Limits: The Rule Nobody Mentions#

This is one of the most important bracket tag rules, and almost no guide mentions it:

Maximum 2-4 bracket tags per section. Beyond that, SUNO starts ignoring tags — and it's not random which ones it drops. Later tags get ignored first, following the same left-to-right priority that governs the Style field.

❌ Too many tags:
[Verse 1]
[whispered]
[acoustic guitar]
[slow tempo]
[reverb heavy]
[emotional]
[intimate]
I remember when you said goodbye...

In this example, SUNO will likely follow [Verse 1] and [whispered], partially follow [acoustic guitar], and completely ignore everything after that. You've wasted four tags.

✅ Focused tags:
[Verse 1]
[whispered, acoustic guitar]
I remember when you said goodbye...

Better. Two clear directives. SUNO follows both consistently.

The Priority Stack

When you use multiple bracket tags in a section, they're processed in this priority order:

1. Section identifier ([Verse], [Chorus], etc.) — always processed first
2. Vocal delivery ([whispered], [belted], [rap]) — second priority
3. Instrumentation ([piano only], [full band]) — third priority
4. Effects/dynamics ([reverb], [building]) — lowest priority, often ignored if the section already has 2-3 tags

This means if you have to choose between a vocal tag and an effects tag, always keep the vocal tag. Vocal delivery instructions have the highest compliance rate after section identifiers.

Combined Style/Structure Tags#

One of the most powerful and underutilized bracket techniques is combining a style descriptor with a structure tag in a single bracket:

[Soft Verse]
[Powerful Chorus]
[Gentle Bridge]
[Explosive Final Chorus]

These combined tags are remarkably effective because they give SUNO two pieces of information in one tag — the section type AND the energy level. Since they count as a single tag against your per-section limit, they're more efficient than using two separate tags.

More examples that work well:

These consistently outperform using two separate tags like [Chorus] followed by [powerful] because they're processed as a unified instruction rather than two competing directives.

V5 Colon Syntax: The New Frontier#

SUNO V5 introduced a new colon-based syntax inside bracket tags that allows for more precise parameter control. This is cutting-edge — most guides haven't covered it yet because V5 is still relatively new.

The syntax is: [Parameter: Value]

[Energy: High]
[Mood: Euphoric]
[Vocals: Layered harmonies]
[Tempo: Accelerating]
[Space: Wide stereo]

This syntax is more explicit than traditional bracket tags. Instead of hoping SUNO interprets "building intensity" correctly, you can specify exactly which parameter you want to modify and what value it should take.

Verified Colon Parameters

Here are the colon parameters we've tested and confirmed work in V5:

Important: Colon syntax tags still count against the 2-4 per-section limit. Don't use six colon tags thinking the new syntax changes the rules — it doesn't.

12 Tags That Work (And 5 That Don't)#

Based on our testing of 308+ bracket tags, here are the most reliable ones:

Tags That Consistently Work

1. `[Instrumental Break]` — Reliably produces a section with no vocals
2. `[a]cappella]` — Removes instruments, vocals only (note: no space before "cappella")
3. `[Whispered]` — One of the most reliable delivery tags
4. `[Belted]` — Powerful, full-voice delivery
5. `[Spoken Word]` — Switches from singing to speaking
6. `[Building Intensity]` — Gradual crescendo through the section
7. `[Guitar Solo]` — Triggers an actual guitar solo passage
8. `[Stripped Back]` — Reduces arrangement to minimal elements
9. `[Double Time]` — Doubles the rhythmic feel
10. `[Half Time]` — Halves the rhythmic feel — great for dramatic drops
11. `[Fade Out]` — Gradually reduces volume at the end
12. `[Stop]` — Creates a brief musical pause (dramatic effect)

Tags That Fail or Produce Inconsistent Results

1. `[120 BPM]` — BPM tags in the Lyrics field are unreliable; put BPM in the Style field instead
2. `[Change key to G minor]` — SUNO doesn't reliably process key change instructions in brackets
3. `[Sound like The Beatles]` — Artist reference tags are inconsistent and may conflict with copyright filters
4. `[Add reverb]` — Too vague; SUNO doesn't process mixing instructions well
5. `[Play faster]` — Relative tempo instructions are unreliable; use [Double Time] instead

The pattern: concrete, visual instructions work. Abstract, technical audio terms fail. SUNO understands "whispered" because it maps to a clear vocal behavior. It doesn't understand "add reverb" because that's a mixing engineer's instruction, not a performance directive.

Tag Stacking: The Advanced Technique#

Tag stacking is the technique of placing multiple bracket tags on separate lines immediately before a section's lyrics. When done correctly (within the 2-4 limit), it creates layered instructions:

[Verse 2]
[hushed, intimate]
[solo piano]
The house is empty now
The echoes fill the hall
I trace your name in dust
Upon the bedroom wall

[Pre-Chorus]
[building intensity]
[full band enters]
But something's changing in the air tonight

[Chorus]
[belted, powerful]
[full band, anthemic]
I won't forget! I won't forgive!
This is the moment that I choose to live!

Notice the progression: hushed verse with solo piano > building pre-chorus with full band > belted chorus at full power. This creates a dynamic arc that makes the song feel like it was arranged by a human producer, not generated randomly.

The Stacking Formula

For maximum impact, stack tags in this order:

1. Section name (required — always first)
2. Vocal delivery + mood (combined in one tag)
3. Instrumentation (what instruments are playing)

This gives you exactly 3 tags per section — well within the safe limit — while covering the three most impactful parameters: structure, performance, and sonic palette.

The Song Editor Advantage#

Manually typing bracket tags is tedious and error-prone. You have to remember which tags work, respect per-section limits, maintain consistent formatting, and build dynamic progression across sections — all while also writing lyrics.

AceTagGen's Song Editor handles all of this. When you use the Questionnaire, the Song Editor step gives you a visual interface with 25+ one-click effects, automatic per-section limit enforcement, and pre-built dynamic progressions. You click "Whispered Verse" and it formats the bracket tag correctly. You click "Build to Chorus" and it adds the right progression tags across sections.

Every tag in the Song Editor comes from our verified database of 308 bracket tags. No guessing, no failed tags, no wasted section limits.

Stop typing brackets by hand. Start directing your songs — try the Questionnaire now.