How the tools decide.

This page describes the analysis used by Rhythm Reader and Rhythm Reader Pro. Other tools on this site use different methods.

Why this page exists

Paste a sentence into Rhythm Reader and it marks the beats. The marks look authoritative. Some rest on a named reference source. Others are engineering decisions that could reasonably have gone another way.

A reader deciding whether to trust a mark, and a researcher deciding whether to use the output as research data, both need to know which is which. The analysis keeps that distinction internally, tagging each step by how well founded it is, and this page carries the distinction out to you.

These labels describe the evidential status of a decision. The three tiers below describe when a decision is made. They are separate classifications: a single tier can contain decisions of differing evidential status.

Three tiers, in order

The analysis runs in three passes, each taking the previous one as input. Keeping them separate matters: a later pass can modify how information from an earlier pass is realized in context, and you can edit any tier without discarding the others.

Tier 1 — what the word brings

Text is first split into words, then each word is looked up in a pronouncing dictionary supplied to the engine when it loads. That dictionary is derived from the CMU Pronouncing Dictionary, a record of General American pronunciations maintained by Carnegie Mellon University. The entry gives the word’s phonemes, with a stress digit on each vowel phoneme — not each vowel letter — so the number of vowel phonemes supplies the syllable count. That much is reference-backed, in the sense that it faithfully reports what the dictionary says. The dictionary itself records pronunciations on which speakers sometimes disagree, so it is a reference, not a ground truth.

Two practical limits follow. The tools ship with a small common-word subset, so an uncommon word may fall through to the fallback analysis rather than being looked up; when that happens the tool says so beneath the text. And the exact dictionary release in use is not currently recorded anywhere in the code or in the exports, which is a reproducibility gap rather than an accuracy one — see the note for researchers below.

The dictionary does not supply syllable boundaries. The tool estimates those with the Maximal Onset Principle, constrained by an explicit table of legal English onsets, plus an exception table where dictionary convention differs. Maximal onset is influential and widely used, but English syllabification has competing analyses and genuine exceptions, so the resulting division is a documented heuristic, not a uniquely correct analysis.

Two further steps are heuristic. Phonemic syllables must be mapped back onto spelling so a mark can sit on the page, and spelling does not divide the way sound does; the alignment rule is an approximation. Words absent from the dictionary get a fallback analysis driven by stress-relevant suffixes.

Each result also carries an internal ranking score. It records how directly the tool reached the result — a single dictionary entry, competing entries that agree, competing entries that disagree, or a fallback analysis — not the probability that the displayed mark is correct. A word with one entry is not thereby more likely to be right; it is only less ambiguously derived.

Tier 2 — the metrical template

Each word’s strong/weak pattern is then matched against the four recurring metrical patterns used on this site, described on the Rhythm page. Where a word carries secondary stress, both readings are kept — secondary treated as full, and secondary reduced — rather than one being chosen silently.

This tier is exploratory, tagged speculative in the code, and the reason is worth stating. Representing a word as a metrical template, and limiting the inventory to four feet, is a modelling decision made partly for teaching. A string such as weak–strong–weak is parsed across a foot boundary rather than given a fifth, word-sized foot of its own. That is defensible and it is not the only defensible choice.

Tier 3 — rhythm in context

Only now does the sentence matter. Words are grouped into phrases, and within each phrase the syllable stream is fitted to the four feet. Lexical stress supplies weighted preferences at this stage; it does not force every word to behave like a complete foot. Feet never cross a phrase boundary, and a phrase may open or close on an incomplete foot, because ordinary prose does not arrive in tidy metrical parcels. These foot-fitting rules are modelling constraints used by the analyser, not established properties of prose rhythm.

Phrase boundaries themselves come from punctuation plus a heuristic: a new phrase opens at a function word that follows at least one content word, with a cap on how long a phrase may run. This produces an editable candidate boundary. It is intended as a useful starting point, not as a validated predictor of where a particular reader would place a boundary. The Phrasing page describes what those boundaries do to meaning.

Function words are demoted at this tier, which is why the and will come out weak in the BAND will PLAY. In a context-neutral reading, function words are often prosodically weak, though contrast can make them prominent — as the Emphasis and focus page shows with He CAN. That broad tendency is well supported (Selkirk, 1996); the particular word list and demotion rule used here are heuristics.

What it will not tell you

Three limits are worth stating outright, because they bound what the tools can be used for.

Emphasis is not modelled. This is the important one, and the code says so outright: contrastive stress is not modelled. The analysis has no representation of what the reader already knows, so it cannot know that Where is MY hamster? differs from WHERE is my hamster?. It assigns one context-free default analysis — which is not the same as a neutral one, since the default itself encodes choices. Everything on the Emphasis and focus page describes work the tools do not do, which is precisely why the marks are editable by hand.

Orthographic syllabification has no single right answer. Where to place a hyphen in spelling is a matter of convention, and dictionaries disagree with each other. The tools follow one convention. Disagreement with it is not necessarily an error in either direction.

A proposal is not a ground truth. Where more than one metrical parse fits nearly as well, the analysis keeps the alternatives rather than hiding them. A displayed pattern is the best available parse under these rules, not the reading. Every beat can be overridden, and the disagreement is often the interesting part.

For researchers

Three properties matter if you are considering using the output in a study. Every analysis records its source and a ranking score, so dictionary-backed marks can be separated from fallback ones. The three tiers can be edited independently — lexical stress, template choice, and phrase boundaries each have their own edit operations, and the analysis reflows afterwards rather than being discarded. And analyses export as CSV and as annotated plain text, so the marks can be checked against your own coding.

What is not yet published is a versioned technical specification: the exact dictionary release, the tokenisation rules, the suffix and exception tables, the ranking formula, the metrical fitting weights and tie-breaking, the phrase-length cap, the full function-word list, and the export schema. The prose above is deliberately readable; it is not sufficient to reproduce an output.

The dictionary is the sharpest instance. The subset shipped with the tools is built from the CMU Pronouncing Dictionary, but the build recipe points at an unpinned branch, so two builds made on different days may not contain the same entries, and no release identifier is written into the shipped file or into any export. Until an analyser version and a dictionary release are recorded in the exports themselves, treat any figure taken from these tools as tied to the copy that produced it, and archive that copy alongside your data.

What does not yet exist is a validation study of the tools themselves. The published work behind this site tested the effects of typographically marked stress and rhythm on readers’ prosodic judgments and sensitivity (Gross, Winegard, & Plotkowski, 2018; Gross, Roldan, Kiessel, Esselink, & Dunlap, 2026). Whether this analyser’s output agrees with trained human coders is a separate question, and an open one. Treat the output as a well-documented proposal to be checked, not as a validated instrument.

Try it

Rhythm Reader shows the result of all three tiers with every syllable tappable. Rhythm Reader Pro exposes the tiers separately, shows phrase structure directly, and lets you move boundaries to watch Tier 3 recompute.

The most informative thing you can do is disagree with it. Where your inner voice and the analysis part company, one of you is responding to something the other is not — and on this site that gap is the subject, not a defect.

References and further reading

The five components are covered in Learn; the claim beneath them is Implicit prosody.